chapter 11: dna and genes · life’s genetic blueprint,” by robert f. weaver, december 1984....

Activities/FeaturesObjectivesSection

Chapter 11 OrganizerChapter 11 Organizer

DNA: The Molecule of HeredityNational Science EducationStandards UCP.1-3, UCP.5;A.1, A.2; B.2, B.3; C.2, C.5;G.1-3 (2 sessions, 1 block)

From DNA to ProteinNational Science EducationStandards UCP.1-3, UCP.5;A.1, A.2; B.2, B.3; C.1, C.2(2 sessions, 2 blocks)

Genetic ChangesNational Science EducationStandards UCP.1-3; A.1,A.2; B.3; C.1, C.2; E.1, E.2;F.1, F.4, F.5; G.1, G.2(2 sessions, 1 block)

1. Analyze the structure of DNA. 2. Determine how the structure of DNA

enables it to reproduce itself accurately.

3. Relate the concept of the gene to thesequences of nucleotides in DNA.

4. Sequence the steps involved in proteinsynthesis.

5. Categorize the different kinds of muta-tions that can occur in DNA.

6. Compare the effects of different kindsof mutations on cells and organisms.

Problem-Solving Lab 11-1, p. 289Inside Story: Copying DNA, p. 292

Problem-Solving Lab 11-2, p. 297MiniLab 11-1: Transcribe and Translate, p. 299Investigate BioLab: RNA Transcription, p. 308

Careers in Biology: Genetic Counselor, p. 303Problem-Solving Lab 11-3, p. 305MiniLab 11-2: Gene Mutations and Proteins,p. 306BioTechnology: Scanning Probe Micro-scopes, p.310

MATERIALS LIST

BioLabp. 308 construction paper (5 colors),scissors, transparent tape, pencil

MiniLabsp. 299 pencil, paper, Table 11.2p. 306 pencil, paper, Table 11.2

Alternative Labp. 294 scissors, yarn (2 skeins), large box

Quick Demosp. 288 large zipperp. 291 large zipper (2)p. 295 students will supplyp. 304 coiled telephone cord, twist ties

Need Materials? Contact Carolina Biological Supply Company at 1-800-334-5551or at http://www.carolina.com

Products Available FromGlencoeTo order the following products,call Glencoe at 1-800-334-7344:Curriculum KitGeoKit: Cells andMicroorganisms

Products Available FromNational Geographic SocietyTo order the following products,call National Geographic Societyat 1-800-368-2728:VideoDNA: Laboratory of Life

Index to NationalGeographic MagazineThe following articles may beused for research relating to thischapter.“The Rise of Life on Earth,” byRichard Monastersky, March1998.“DNA Profiling: The New Scienceof Identity,” by CassandraFranklin-Barbajosa, May 1992.“Beyond Supermouse: ChangingLife’s Genetic Blueprint,” byRobert F. Weaver, December1984.

Teacher’s Corner

286B286A

DNA and GenesDNA and Genes

TransparenciesReproducible MastersSection

DNA: TheMolecule of Heredity

From DNA toProtein

Genetic Changes

Section 11.1

Section 11.2

Section 11.3

Teacher Classroom Resources

Reinforcement and Study Guide, p. 47Concept Mapping, p. 11Laboratory Manual, pp. 75-78

Reinforcement and Study Guide, pp. 48-49Critical Thinking/Problem Solving, p. 11BioLab and MiniLab Worksheets, pp. 49-50Content Mastery, pp. 53, 55-56

Reinforcement and Study Guide, p. 50BioLab and MiniLab Worksheets, pp. 51-56Laboratory Manual, pp. 79-82Content Mastery, pp. 53-55, 56 L1

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Section Focus Transparency 26Basic Concepts Transparency 16

Section Focus Transparency 27Basic Concepts Transparency 17Basic Concepts Transparency 18Reteaching Skills Transparency 18

Section Focus Transparency 28Reteaching Skills Transparency 19a, 19b

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Assessment Resources Additional ResourcesSpanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block Scheduling

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Chapter Assessment, pp. 61-66MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomComputer Test BankBDOL Interactive CD-ROM, Chapter 11 quiz

Section 11.2

Section 11.1

Section 11.3

Refer to pages 4T-5T of the Teacher Guide for an explanation of the National Science Education Standards correlations.

Key to Teaching StrategiesKey to Teaching Strategies

Level 1 activities should be appropriatefor students with learning difficulties.Level 2 activities should be within theability range of all students.Level 3 activities are designed for above-average students.ELL activities should be within the abilityrange of English Language Learners.

Cooperative Learning activitiesare designed for small group work.These strategies represent student prod-ucts that can be placed into a best-workportfolio.These strategies are useful in a blockscheduling format.

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The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

Animation: DNA ReplicationAnimation: TranscriptionAnimation: TranslationExploration: MutationsBioQuest: Building a Protein

Videodisc ProgramDNA ReplicationDNA TranscriptionTranslation

The Infinite VoyageUnseen Worlds

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http://www.carolina.com

Section

What is DNA? Although the environment influ-

ences how an organism develops, thegenetic information that is held inthe molecules of DNA ultimatelydetermines an organism’s traits.DNA achieves its control by produc-ing proteins. Living things containproteins. Your skin contains protein,your muscles contain protein, andyour bones contain protein mixedwith minerals. All actions, such aseating, running, and even thinking,depend on proteins called enzymes.Enzymes are critical for an organ-

ism’s function because they controlthe chemical reactions needed forlife. Within the structure of DNA isthe information for life—the com-plete instructions for manufacturingall the proteins for an organism.

The structure of DNADNA is capable of holding all this

information because it is a very longmolecule. Recall that DNA is a poly-mer made of repeating subunitscalled nucleotides. Nucleotides havethree parts: a simple sugar, a phos-phate group, and a nitrogen base.The simple sugar in DNA, called

11.1 DNA: THE MOLECULE OF HEREDITY 287

Can you imagine all of the information that could be con-tained in 1000 textbooks?

Remarkably, that much information—and more—is carried by the genes of asingle organism. Scientists have foundthat the substance DNA, contained ingenes, holds this information. Because ofthe unique structure of DNA, newcopies of the information can be easilyreproduced.

SECTION PREVIEW

ObjectivesAnalyze the structureof DNA.Determine how thestructure of DNAenables it to reproduceitself accurately.

Vocabularynitrogen basedouble helixDNA replication

11.1 DNA: The Molecule of Heredity

Model of a DNA molecule

287

Section 11.1

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

HO

CH2

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OH H

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Nitrogenbase

Phosphate

Deoxyribosesugar

DNA nucleotide

Use with Chapter 11,Section 11.1

What are the three components of this DNA nucleotide?

What is the function of DNA in the cell?

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Transparency DNA Structure26 SECTION FOCUS

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PrepareKey ConceptsThe structure and composition ofDNA are presented. The processof replication of DNA and itsimportance to organisms areemphasized.

Planning■ Collect photos of Drosophila

mutations for the GettingStarted Demo.

■ Purchase two large zippers forthe Quick Demos.

■ Collect modeling clay, coloredpaperclips, and twist ties orpipe cleaners for the DNAModel Project.

■ Gather index cards and rubberbands for the Flip Books Pro-ject.

■ Make a set of cards for Re-teach.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 26 on the overhead pro-jector and have students answerthe accompanying questions.

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Assessment PlannerAssessment PlannerPortfolio Assessment

Portfolio, TWE, pp. 289, 300, 305BioLab, TWE, pp. 308-309

Performance AssessmentAssessment, TWE, pp. 291, 304Problem-Solving Lab, TWE, p. 305MiniLab, TWE, p. 306MiniLab, SE, pp. 299, 306BioLab, SE, pp. 308-309Alternative Lab, TWE, pp. 294-295

Knowledge AssessmentProblem-Solving Lab, TWE, pp. 289, 297Assessment, TWE, pp. 293, 300, 301, 307Section Assessment, SE, pp. 293, 301, 307Chapter Assessment, SE, pp. 311-313

Skill AssessmentAlternative Lab, TWE, pp. 294-295MiniLab, TWE, p. 299

286 DNA AND GENES

DNA and Genes

What You’ll Learn■ You will relate the structure

of DNA to its function. ■ You will explain the role of

DNA in protein production.■ You will distinguish among

different types of mutations.

Why It’s ImportantAn understanding of birthdefects, viral diseases, cancer,aging, genetic engineering,and even criminal investiga-tions depends upon knowingabout DNA, how it holds infor-mation, and how it plays a rolein protein production.

Fly MutationsCompare the small photo of anormal fruit fly with the largephoto of a fruit fly that has amutation. How are the flies dif-ferent? The parents of themutated fly had normal geno-types. How do you think this flyended up this way?

To find outmore about

DNA and genes, visit theGlencoe Science Web Site. www.glencoe.com/sec/science

11

GETTING STARTEDGETTING STARTED

ChapterChapter

The appearance of thesetwo flies depends on thetype of genes they con-tain. Chromosomes,made of genes, which aremade of DNA, determinehow an organism looksand how it functions.

286

Theme DevelopmentThe first section of this chapterstresses homeostasis, or stability.DNA contains the blueprints forlife, and replication processesmake exact copies of these blue-prints. The second section illus-trates unity within diversity; theprocess and the code by which acell makes proteins are the samein all species. The third sectionillustrates how homeostasis canbe disrupted when mutationsoccur. Change in the DNA canbe harmful, but changes areresponsible for the evolution of aspecies.

Chapter 11Chapter 11

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Project, pp. 288,300; Reteach, p. 293; Quick

Demo, p. 295; Extension, p. 301Visual-Spatial Quick Demo, p. 291; Project, p. 292; Rein-

forcement, p. 298; Reteach, p. 301;Meeting Individual Needs, p. 304

Interpersonal Tech Prep, p. 303

Intrapersonal Enrichment, pp. 288, 296; Biology Journal,

p. 306; Going Further, p. 310Linguistic Portfolio, pp. 289,300, 305; Enrichment, p. 290;

Biology Journal, pp. 291, 299, 302Logical-Mathematical Enrich-ment, p. 303; Reinforcement,

p. 304

GETTING STARTED DEMOGETTING STARTED DEMO

Show students photographs ofother fruit fly mutations such asvarious eye colors and wingshapes. Ask students to shareways that the flies could havereceived the mutations. Explainthat various environmental factors, such as radiation andchemicals, can cause mutations.Guide the discussion to the concept of the DNA molecule,which serves as the blueprintfor life.

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If time does not permit teach-ing the entire chapter, use theBioDigest at the end of theunit as an overview.

http://www.glencoe.com/sec/science

thymine are always present in equalamounts. Likewise, the guanine andcytosine base pairs result in equalamounts of these nucleotides inDNA. Watson and Crick also pro-posed that DNA is shaped like a longzipper that is twisted. When some-thing is twisted like a coiled spring,the shape is called a helix. BecauseDNA is composed of two strandstwisted together, its shape is called adouble helix. This shape is shown inFigure 11.2.


Figure 11.2DNA normally exists in the shape of adouble helix. This shape is similar to thatof a twisted zipper.

What does chemical analysis reveal about DNA? Muchof the early research on the structure and composition ofDNA was done by carrying out chemical analyses. The datafrom these experiments provide evidence of a relationshipamong the nitrogen bases of DNA.

AnalysisExamine Table 11.1. Compare the amounts of adenine,

guanine, cytosine, and thymine found in the DNA of each ofthe cells studied.

Thinking Critically1. Compare the amounts of A, T, G, and C in each kind

of DNA. Why do you think the relative amounts are sosimilar in human liver and thymus cells?

2. How do the relative amounts of each base in herring spermcompare with the relative amounts of each base in yeast?

3. What fact can you state about the overall composition ofDNA, regardless of its source?

Problem-Solving Lab 11-1Problem-Solving Lab 11-1 Interpreting the Data

OriginWORDWORD

helixFrom the Latinword helix, meaning“spiral.” A doublehelix has twotwisted strands thatform a spiral.

The importance of nucleotide sequences

An elm, an elk, and an eel are alldifferent organisms composed of dif-ferent proteins. If you compare thechromosomes of these organisms, youwill find that they all contain DNAmade up of nucleotides with adenine,thymine, guanine, and cytosine bases.How can organisms be so differentfrom each other if their geneticmaterial is made of the same fournucleotides? Their differences result

Source of sample TCGA

Human liver

Human thymus

Herring sperm

Yeast

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Table 11.1 Percent of each base in DNA samples

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Concept DevelopmentPoint out to students that thewords elm, elk, and eel differ fromeach other by only one letter butthat the meaning of the words isdrastically different. This obser-vation can introduce the impor-tance of base sequences.

PurposeStudents will analyze a tableshowing the percentages of fourbases in DNA samples.

Process Skillscompare and contrast, observeand infer, interpret data

BackgroundIn 1950, American biochemistErwin Chargaff first showed thatthere is a 1:1 ratio between ade-nine and thymine and betweenguanine and cytosine in all DNA.

Teaching Strategies■ Guide students to compare thenumbers within each samplebefore comparing different sam-ples.

Thinking Critically

1. The ratio of A:T and of C:Gis approximately 1:1. The rel-ative amounts of each baseare so similar in human liverand thymus because theycome from the same species.

2. The relative amounts of eachbase are different in herringand in yeast because they aredifferent species.

3. The ratio of A:T and G:C is1:1 for all sources.

Knowledge Have studentssummarize their analysis of thedata and write a paragraphexplaining why the ratio of baseswas important in determining thestructure of DNA. Use thePerformance Task AssessmentList for Writing in Science inPASC, p. 87. L2

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Problem-Solving Lab 11-1Problem-Solving Lab 11-1

deoxyribose (dee ahk sih RI bos),gives DNA its name—deoxyribonu-cleic acid. The phosphate group iscomposed of one atom of phosphorussurrounded by four oxygen atoms. Anitrogen base is a carbon ring struc-ture that contains one or more atomsof nitrogen. In DNA, there are fourpossible nitrogen bases: adenine (A),guanine (G), cytosine (C), andthymine (T). Thus, in DNA thereare four possible nucleotides, eachcontaining one of these four bases, asshown in Figure 11.1.

Nucleotides join together to formlong chains, with the phosphategroup of one nucleotide bonding tothe deoxyribose sugar of an adjacentnucleotide. The phosphate groupsand deoxyribose molecules form thebackbone of the chain, and the nitro-gen bases stick out like teeth on azipper. In DNA, the amount of ade-nine is always equal to the amount ofthymine, and the amount of guanineis always equal to the amount of

cytosine. You can see this in theProblem-Solving Lab on the next page.

In 1953, James Watson andFrancis Crick published a journalarticle that was only one page inlength, yet monumental in impor-tance. Watson and Crick proposedthat DNA is made of two chains ofnucleotides joined together by thenitrogen bases. Just as the teeth of azipper hold the two sides of the zip-per together, the nitrogen bases ofthe nucleotides hold the two strandsof DNA together with weak hydro-gen bonds. The two strands can beheld together in this way becausethey are complementary to eachother; that is, the bases on one stranddetermine the bases on the otherstrand. Specifically, adenine on onestrand bonds with a thymine on theother strand, and guanine on onestrand bonds with a cytosine on theother strand. These two bondedbases, called a complementary basepair, explain why adenine and

288 DNA AND GENES

Figure 11.1Adenine and guanine aredouble-ring bases calledpurines (A). Thymine andcytosine are smaller, single-ring bases called pyrim-idines (B). Each of the fournucleotides that make upDNA contains a phosphategroup, the sugar deoxyri-bose, and one of four dif-ferent nitrogen bases (C).

Purines Pyrimidines

Nucleotide

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2 TeachDiscussionAsk students whether they knowwhy each of them is a uniqueindividual. Students may suggestthat hereditary factors determinetheir uniqueness. Why has therebeen no other human on Earthexactly like any of them? Eachindividual has different DNA andthus different traits.

EnrichmentIntrapersonal Have studentsresearch one of the people

involved in the discovery of thestructure and function of DNA:Fred Griffith, O.T. Avery, AlfredHershey, Linus Pauling, MarthaChase, Erwin Chargaff, RosalindFranklin, or Maurice Wilkins.Have students prepare short oralreports on what these scientistscontributed. L3

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Quick DemoQuick Demo

Hold up a large unzipped zip-per and relate the zipper teethto the nucleotides and thecloth band to the deoxyribose-phosphate backbone. Explainthat in DNA, hydrogen bondsbetween the nucleotides holdthe two strands together. Zipthe zipper to show how theDNA looks when the nucleo-tides are hydrogen-bonded.Then twist the ends of the zipper to show how DNA istwisted into a helix.

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P R O J E C TDNA Model

Kinesthetic Have student groups maketwo strands of modeling clay, each

about 8 cm long and 1 cm thick. Each groupwill need five each of four different colors ofpaper clips to represent the DNA bases.Assign letters to the colors so that eachgroup has 5 A-clips, 5 T-clips, 5 C-clips, and 5G-clips. Students should poke half of the

clips in a row into one of the clay strands. Onthe second clay strand, they should line upthe complementary clips in the proper order(A = T, C = G). Have them connect the baseswith pipe cleaners or twist ties. Once themodel is bonded together, it can be twistedto suggest the double helix structure of DNA.

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PortfolioPortfolio

DNA Connection Linguistic Have students read“Happy Birthday Double Helix” by

Leon Jaroff, Time, March 15, 1993, pp.56-59. Have them write a summary of howthe discovery of DNA’s structure has beenapplied to other fields, such as industryand business.

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Resource ManagerResource Manager

Section Focus Transparency 26and Master

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Laboratory Manual, pp. 75-78 L2

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would have only half the DNA oftheir parents. Species could not sur-vive, and individuals could not growor reproduce successfully. All organ-isms undergo DNA replication.Figure 11.4B shows bacterial DNAreplicating.

How DNA replicatesYou have learned that a DNA mol-

ecule is composed of two strands,each containing a sequence ofnucleotides. As you know, an adenineon one strand pairs with a thymineon the other strand. Similarly, gua-nine pairs with cytosine. Therefore,if you knew the order of bases on onestrand, you could predict thesequence of bases on the other, com-plementary strand. In fact, part of theprocess of DNA replication is donein just the same way. During replica-tion, each strand serves as a patternto make a new DNA molecule. Howcan a molecule serve as a pattern?Read the Inside Story on the next pageto find out.

DNA replication begins as anenzyme breaks the hydrogen bondsbetween nitrogen bases that hold thetwo strands together, thus unzippingthe DNA molecule. As the DNAcontinues to unzip, nucleotides thatare floating free in the surroundingmedium bond to the single strands bybase pairing. Another enzyme bondsthese new nucleotides into a chain.

This process continues until theentire molecule has been unzippedand replicated. Each new strandformed is a complement of one of theoriginal, or parent, strands. Theresult is the formation of two DNAmolecules, each of which is identicalto the original DNA molecule.

When all the DNA in all the chro-mosomes of the cell has been copiedby replication, there are two copiesof the organism’s genetic informa-tion. In this way, the genetic makeupof an organism can be passed on tonew cells during mitosis or to newgenerations through meiosis followedby sexual reproduction.


Replication

DNA

Replication

Figure 11.4DNA replication producestwo molecules from one.

When a DNA mole-cule replicates, two molecules areformed. Each mole-cule has one origi-nal strand and one new strand.Newly-synthesizedstrands are shownin red.

AA

This circular bacterial DNA is replicating. Thephoto shows two loops. The bottom loop istwisted into a figure-8 shape. Replication istaking place at the intersections of the twoloops, as indicated by the arrows.

BB

Magnification: 188 000�

291

from the sequence of the four differ-ent nucleotides along the DNAstrands, as you can see in Figure 11.3.

The sequence of nucleotides formsthe unique genetic information of anorganism. For example, a nucleotidesequence of A-T-T-G-A-C carriesdifferent information from asequence of T-C-C-A-A-A. In a simi-lar way, two six-letter words made ofthe same letters but arranged in dif-ferent order have different meanings.The closer the relationship betweentwo organisms, the greater the simi-larity in their order of DNAnucleotides. The DNA sequences of

a chimpanzee are similar to those of agorilla, but different from those of arose bush. Scientists use nucleotidesequences to determine evolutionaryrelationships among organisms.Nucleotide sequences can also beused to determine whether two peo-ple are related, or whether the DNAin a blood sample matches the DNAof a suspected criminal.

Replication of DNAA sperm cell and an egg cell of a

fruit fly, both produced throughmeiosis, unite to form a fertilized egg.From one fertilized egg, a fruit flywith billions of cells is produced bythe process of mitosis. Each cell has acopy of the DNA that was in theoriginal fertilized egg. As you havelearned, before a cell can divide bymitosis or meiosis, it must first makea copy of its chromosomes. TheDNA in the chromosomes is copiedin a process called DNA replication.Without DNA replication, new cells

290 DNA AND GENES

Figure 11.3The structure of DNAis shown here.

In each chain of nucleotides,the sugar of one nucleotideis joined to the phosphategroup of the next nucleotideby a covalent bond.

AA The two chains ofnucleotides in a DNA mole-cule are held together byhydrogen bonds betweenthe bases. In DNA, cytosine

forms hydrogen bondswith guanine, and

thymine bonds withadenine.

BB

This pairing produces a long, two-stranded molecule that is often com-pared to a zipper. As you can see, thesides of the zipper are formed by thesugar and phosphate units, while theteeth of the zipper are the pairs of bases.

CC

Sugar-phosphate backbone

Hydrogen bonds betweennitrogen bases

Chromosome

A

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Cultural DiversityHar Gobind KhoranaTeach students about some of the experimen-tal methods scientists have used to decipherthe genetic code. In particular, explain theresearch of Indian-American biochemist, HarGobind Khorana. In the 1960s, Khoranademonstrated that genes could be manufac-

tured in the laboratory. Khorana’s artificialgenes were able to code for the synthesis of proteins just as they do in living cells. This work ultimately led to the cracking of aportion of the genetic code. For this work,Khorana and colleagues received the NobelPrize for Physiology or Medicine in 1968.


Visual-Spatial Hold up azipped zipper. Help stu-

dents realize that to make acopy, the DNA must unzip. Thenucleotides separate along thehydrogen bonds. Unzip thezipper to show this. Then havetwo students each carry over azipper half and show how theywould align the halves to theexposed teeth of the original“DNA molecule.” They will notbe able to zip the zipper halvestogether, so the studentsshould hold them in place.P

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MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Learning DisabledThere are many details involved in replica-tion, so it is important to help studentskeep the big idea in mind: DNA mustmake copies of itself so cells can repro-duce.

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BIOLOGY JOURNAL BIOLOGY JOURNAL

Semi-Conservative ReplicationLinguistic The process of DNA repli-cation is often called semi-conserva-

tive. Have students think about andexplain in their journals what that means.When DNA replicates into two molecules,each new DNA molecule is made of oneold and one new strand.

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VIDEODISCVIDEOTAPEThe Secret of Life

Sex and the Single Gene: CellDevelopment

VIDEODISC The Secret of LifeDNA: Structure and

Replication

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!;,sMN8C"

EnrichmentLinguistic Interested stu-dents can read The Double

Helix, in which James D. Watsontells the story of the discovery ofthe structure of DNA. Watsonpresents a story of scientists aspeople with human feelings, notthe stereotypical image of scien-tists in white lab coats who live intheir laboratories. Watson alsodiscusses the highly competitiveand jealous rivalry that occurs inthe scientific community.

Chalkboard ExampleVisual-Spatial On the chalk-board, draw and label one

strand of DNA. Have studentscopy this and draw the comple-mentary strand. Make sure theyunderstand that adenine pairsonly with thymine and that gua-nine pairs only with cytosine.After the students have com-pleted their diagrams, draw thecomplementary strand on thechalkboard. L1

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CD-ROMBiology: The Dynamicsof Life

Animation: DNA ReplicationDisc 2

Performance Assessmentin the Biology Classroom, p. 17,Building a Model of Replication.Have students carry out thisactivity after they have learnedabout DNA replication. L1

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VIDEODISCBiology: The Dynamicsof Life

DNA Replication (Ch. 31)Disc 1, Side 145 sec.!:6Ç"

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Free nucleotides

New DNA strand

New DNA strand

New DNA molecule

New DNA molecule

AA

TG

G

C

C


Bonding of bases Thesugar and phosphate partsof adjacent nucleotidesbond together to form thebackbone of the new strand.Each original strand is nowbonded to a new strand.

33

Results of replication The process of repli-cation produces two molecules of DNA. Eachnew molecule has one strand from the originalmolecule and one strand that has been newlysynthesized from free nucleotides in the cell.

44

Section AssessmentSection Assessment

Understanding Main Ideas1. Describe the structure of a nucleotide.2. How do the nucleotides in DNA pair?3. Explain why the structure of a DNA molecule is

often described as a zipper.4. How does DNA hold information?

Thinking Critically5. The sequence of nitrogen bases on one strand

of a DNA molecule is GGCAGTTCATGC. What would be the sequence of bases on the comple-mentary strand?

6. Sequencing Sequence the steps that occur during DNA replication. For more help, refer to Organizing Information in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

293

3 AssessCheck for UnderstandingHave students each write twoquestions about the process ofDNA replication. Collect thequestions and use them to quizthe class.

ReteachKinesthetic Divide the classinto four equal groups. Give

each group a letter name—A, T,G, or C. Give each student a cardwith his or her letter. Write abase sequence for one strand of aDNA molecule on the chalk-board. Be sure to write as manybases as there are students. Givestudents two minutes to line upnext to the appropriate comple-mentary letter on the chalkboard.Tell them they have just repli-cated a DNA molecule.

ExtensionHave students research the workof Frederick Griffith in 1928 andOswald Avery and his colleaguesin 1944. These scientists demon-strated that DNA is the geneticmaterial.

Knowledge Prepare asheet showing a short section oftwo-stranded DNA. Ask studentsto diagram the steps this shortsection would go through inorder to replicate.

4 CloseDiscussionAsk students how the DNAstructure lends itself to replica-tion. Why is accuracy so impor-tant in replication? L2

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Section AssessmentSection AssessmentSection Assessment1. A nucleotide consists of a sugar, a phos-

phate group, and a nitrogen base.2. Cytosine forms hydrogen bonds with

guanine; thymine bonds with adenine.3. The molecule is shaped like a twisted zip-

per with the sides formed by the sugarand phosphate molecules. The teeth ofthe zipper are the pairs of bases.

4. The information is held in the sequence

of nucleotides.5. CCGTCAAGTACG6. The two strands separate at the base

pairs. Free complementary nucleotidesare attracted to those on the strands.Enzymes join the new nucleotides toform strands complementary to the origi-nal strands. Two new double-strandedmolecules separate.

D

P

D

P

D

P

P

D

D

P

D

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Original DNA strand

Original DNA

A

A

A

T

T

T

T

G

G

C

C

C

292 DNA AND GENES

Copying DNA

DNA is copied during interphase prior tomitosis and meiosis. It is important that

the new copies are exactly like the original molecules. The structure of DNA provides amechanism for accurate copying of the molecule.The process of making copies of DNA is calledDNA replication.

Critical Thinking What would be the outcome if mitosis occurred before replicationtook place?

Two molecules of DNA from one

INSIDESSTORTORYY

INSIDE

Separation of strands When a cell begins tocopy its DNA, the two nucleotide strands of aDNA molecule first separate at their base pairswhen the hydrogen bonds connecting the basepairs are broken. As the DNA molecule unzips,the nucleotides are exposed.

11

Base pairing Free nucleotides base pair withexposed nucleotides. If one nucleotide on astrand has thymine as a base, the free nucleotidethat pairs with it would be adenine. If the strandcontains cytosine, a free guanine nucleotide willpair with it. Thus, each strand builds its comple-ment by base pairing with free nucleotides.

22

Magnification:280 000�

292

IINSIDENSIDESSTORTORYY

INSIDE

PurposeStudents study the steps involvedin the replication of DNA.

Teaching Strategies■ Have students write a one-paragraph summary of the eventsin replication.■ Have students write a singlestrand sequence and exchange itwith a partner. The partnershould write the complementarystrand and return it to the firststudent to be checked.

Visual Learning■ Have students draw the steps

of replication as separate dia-grams.

Critical ThinkingThe most likely occurrence isthat both daughter cells would bemissing some of their chromo-somes and would not be able tolive. Another possibility is thatone cell would get the completeset of chromosomes and couldlive and function. The other cellwould get no chromosomes andwould die.

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P R O J E C TFlip Books

Visual-Spatial Have students createanimated flip books showing replica-

tion by drawing scenes near the edges of astack of index cards. They should show DNAunzipping, individual nucleotides bonding to

the exposed strands, and the formation oftwo DNA molecules. The stack can be heldtogether with a rubber band. Have studentsshare their “films” with classmates.P

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Finally, both DNA and RNA containfour nitrogen bases, but rather thanthymine, RNA contains a similarbase called uracil (U). The uracilforms a base pair with adenine, just asthymine does in DNA.

What is the role of RNA in thecell? Let’s look at an analogy. Perhapsyou have seen a car being built on anautomobile assembly line. Complexautomobiles are built in many simplesteps. Engineers tell workers how tomake the cars, and the workers fol-low directions to build the cars onthe assembly line. Suppliers bringparts to the assembly line so they canbe installed in the car. Protein pro-duction is similar to car production.DNA provides workers with the

instructions for making the proteins,and the workers build the proteins.Other workers bring parts, the aminoacids, over to the assembly line. Theworkers for protein synthesis areRNA molecules. They take fromDNA the instructions on how theprotein should be assembled, then—amino acid by amino acid—theyassemble the protein.

There are three types of RNA thathelp to build proteins. Extending thecar-making analogy, you can considerthese RNA molecules to be theworkers in the protein assembly line.One type of RNA, messenger RNA(mRNA) brings information from theDNA in the nucleus to the cell’s factory floor, the cytoplasm. On the

11.2 FROM DNA TO PROTEIN 295

Figure 11.5The three chemicaldifferences betweenDNA and RNA areshown here.

RNA contains the nitrogen base uracil (U)in place of thymine (T). Uracil base pairswith adenine just as thymine does in DNA.

CC

The sugar in RNA isribose, rather thanthe deoxyribosesugar of DNA.

BB

An RNA molecule usually consists of asingle strand of nucleotides, not a doublestrand. This single-stranded structure isclosely related to its function.

AA

CH

C

C

N

N

O

O

H

C

HO CH2

O = P – O

C

Hydrogenbonds

Adenine

Uracil

Ribose

A

Phosphate

H

OH OH

H

O

H

O

N

N

N

N

N

H

H

H

C

C C

C

CH

C C

C

P

R

C

P

RU

RG

2 Teach

Tying to PreviousKnowledgeHave students recall the structureof proteins, amino acids, poly-peptides, and peptide bond for-mation from Chapter 6. Makesure students understand thatmost proteins require the synthe-sis of two or more polypeptidechains.

Section

294 DNA AND GENES

Genes and ProteinsThe sequences of nucleotides in

DNA contain information. Thisinformation is put to work throughthe production of proteins. Proteinsform into complex three-dimensionalshapes to become key cell structuresand regulators of cell functions.Some proteins become importantstructures, such as the filaments inmuscle tissue, walls of blood vessels,and transport proteins in membranes.Other proteins, such as enzymes,control chemical reactions that per-form key life functions—breakingdown glucose molecules in cellularrespiration, digesting food, or mak-ing spindle fibers during mitosis. Infact, enzymes control all the chemicalreactions of an organism. Thus, by

encoding the instructions for makingproteins, DNA controls cells.

You learned earlier that proteinsare polymers of amino acids. Thesequence of nucleotides in each genecontains information for assemblingthe string of amino acids that makeup a single protein. It is estimatedthat each human cell contains about80 000 genes.

RNARNA, like DNA, is a nucleic acid.

However, RNA structure differs fromDNA structure in three ways, shownin Figure 11.5. First, RNA is singlestranded—it looks like only one-halfa zipper—whereas DNA is doublestranded. The sugar in RNA isribose; DNA has deoxyribose.

Morse code was a method ofcommunicating that wasdeveloped in the nineteenth

century. This code used a pattern ofdots and dashes to represent letters of the alphabet. In this way, long se-quences of dots and dashes could pro-duce an infinite number of differentmessages. Living organisms havetheir own code, called the geneticcode, in which the sequence ofnucleotides in DNA can beconverted to the sequence ofamino acids in proteins.

SECTION PREVIEW

ObjectivesRelate the concept ofthe gene to thesequences ofnucleotides in DNA.Sequence the stepsinvolved in protein synthesis.

Vocabularymessenger RNAribosomal RNAtransfer RNAtranscriptioncodontranslation

11.2 From DNA to ProteinSign

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

Signal Sign

S

T

U

V

W

X

Y

Z

1

2

3

4

5

6

7

8

9

0

Signal

This sample ofMorse code (above)is being sent (inset).

294

Section 11.2

PrepareKey ConceptsStudents will learn how DNA,genes, and proteins are related.The relationship between genesand the nucleotide sequences inDNA is discussed. Finally, thesteps involved in the formation ofmRNA and the role of tRNA intranslation are explained.

Planning■ Buy yarn and bring in a box

for the Alternative Lab.■ Purchase or photocopy blank

bingo cards for the Reinforce-ment.

■ Purchase or gather five colorsof construction paper for theBioLab.

■ Locate a combination lock forthe Meeting Individual Needs.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 27 on the overhead pro-jector and have the studentsanswer the accompanying ques-tions.

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How are these pieces of music similar?

How do they differ? What is the result of this difference?

11

22

Transparency Using Codes27 SECTION FOCUS

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Kinesthetic Have a fewstudents simulate the

assembly line manufacture of“widgets.” Some studentsbring design plans to theassembly line, others bringsupplies to the line, and stillothers do the assembly on theline. Relate this to the manu-facture of proteins.

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Expected ResultsThe total length of all the yarn pieces, 1500m, represents the length of DNA in a bac-terium if the cell were scaled up to the sizeof the box.Analysis

1. Compare the length of DNA with thesize of the “cell” (box). How does allthe DNA fit inside the cell? The DNA iscoiled and twisted.

2. A human cell contains about 80 000

genes. How long would the yarn bethat represents all the DNA in a humancell? 80 000 � 40 cm = 32 000 m

Skill Ask students to write a labreport and calculate the answers to theanalysis questions. Use the PerformanceTask Assessment List for Using Math inScience in PASC, p. 29.


Alternative Lab Gene and Chromosome Size

PurposeStudents will conceptualize the size of a geneand a bacterial chromosome by constructingyarn models that are scaled up a million timesin size.Materials 2 skeins of 3-ply yarn for a class of 20-30,

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scissors, box about 100 cm � 50 cmProcedureGive students the following directions.

1. One nucleotide in a molecule of DNAoccupies a length of 3.4 � 10–10 m. If anaverage gene coding for an average-sizedprotein contains 1200 base pairs, howlong is an average gene? 3.4 � 10–10 m � 1200 = 4.08 � 10–7 mHow many amino acids would thesenucleotides code for? 1200 bases � 3

bases per codon = 400 codons = 400amino acids

2. Cut a piece of yarn 40 cm long to rep-resent the average gene. This length is1 000 000 times that of a gene.

3. Cut a piece of yarn that would repre-sent 150 genes. 150 � 40 cm = 60 mTie the end of your 60-m piece of yarnto another until all yarn strands in theclass are connected.

295


Critical Thinking/ProblemSolving, p. 11

Concept Mapping, p. 11

Section Focus Transparency 27and Master

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The main difference is that transcrip-tion results in the formation of onesingle-stranded RNA molecule ratherthan a double-stranded DNA mole-cule. You can find out how scientistsuse new microscopes to “watch”transcription take place by readingthe BioTechnology at the end of thechapter. Modeling the process oftranscription in the BioLab will helpyou to understand this process.

The Genetic CodeThe nucleotide sequence tran-

scripted from DNA to a strand ofmessenger RNA acts as a geneticmessage, the complete informationfor the building of a protein. Thinkof this message as being written in alanguage that uses nitrogen bases asits alphabet. As you know, proteinsare built from chains of smaller mol-ecules called amino acids. You couldsay that the language of proteins usesan alphabet of amino acids. A code isneeded to convert the language ofmRNA into the language of proteins.There are 20 different amino acids,but mRNA contains only four typesof bases. How can these bases form acode for proteins? Biochemists beganto crack the code when they realizedthat a group of three nucleotidescodes for one amino acid. For exam-ple, a sequence of three uracilnucleotides in mRNA (U-U-U)results in the amino acid phenylala-nine being placed in a protein. Eachset of three nitrogen bases in mRNArepresenting an amino acid is knownas a codon. You can follow the bio-chemists’ reasoning for why threebases are needed by doing theProblem-Solving Lab on this page.

The order of nitrogen bases in themRNA will determine the type andorder of amino acids in a protein.Sixty-four combinations are possible


How many nitrogen bases determine an amino acid?After the structure of DNA had been discovered, scientists triedto predict the number of nucleotides that code for a singleamino acid. It was already known that there were 20 aminoacids, so at least 20 codons were needed. If one nucleotidecoded for an amino acid, then only four amino acids could berepresented. How many nucleotides are needed?

AnalysisExamine the

three safes. Letters representing nitrogen bases have replaced numbers on the dials. Copy the data table. Calculate the possible number of combinations that will open the safe in each dia-gram using the formula provided in the table. The 4 corre-sponds to the number of letters on each dial; the superscriptrefers to the number of available dials.

Thinking Critically 1. Using safe 1, write down several examples of dial settings

that might open the safe. Do the total possible combina-tions seen in safe 1 equal or surpass the total number ofamino acids known?

2. Could a nitrogen base (A, T, C, or G) taken one at a timecode for 20 different amino acids? Explain.

3. Using safe 2, write down several examples of dial combi-nations that might open the safe. Do the total possiblecombinations seen in safe 2 equal or surpass the totalnumber of amino acids known?

4. Could nitrogen bases taken two at a time code for 20 different amino acids? Explain.

5. Using the same procedure for safe 3, see whether thetotal possible combinations equal or surpass the totalnumber of amino acids known.

6. Could nitrogen bases taken three at a time code for 20different amino acids? Explain.

7. Does the analogy prove that three bases code for anamino acid? Explain.

Problem-Solving Lab 11-2Problem-Solving Lab 11-2 Formulating Models

Formula

Totalpossible

combinations

Number of lettersper dial

Numberof dials

Safe 1

Safe 2

Safe 3

41

42

43

Data Table

T

G

C

A

T

G

C

A

T

G

C

A T

G

C

A

T

G

C

A

T

G

C

A

Safe 1 Safe 2 Safe 3

PurposeStudents will use an analogy tosee that at least three nitrogenbases are required to code for asingle amino acid.

Process Skillsanalyze information, apply con-cepts, collect data, compare andcontrast, draw a conclusion,interpret data, predict, think crit-ically, use numbers

BackgroundThe coding for amino acids usingthree nitrogen bases is said to beredundant. That is, there can beseveral different codons that codefor the same amino acid. Thus,the number of combinations is ashigh as 61 (64 if stops are consid-ered). The number 64 agreesperfectly when three of any fournitrogen bases combine in anyorder to code for an amino acid.

Teaching Strategies■ Remind students that there are20 amino acids. ■ You may wish to have studentsdetermine the number of two-letter combinations without theuse of the formula. It may not bepractical, however, to have themactually determine the number ofcombinations for a three-dialsafe.

Thinking Critically

1. A or T or C or G; no2. No, there are 20 amino acids

and only 4 different codesusing 1 letter.

3. AA, AT, CT, CG, etc; no4. No, there are 20 amino acids

and only 16 different codesusing 2 letters.

5. ATT, ATC, ATG, ATA, etc;yes

6. Yes, there are 20 amino acidsand 64 possible combinationsusing 3 letters.

7. No, it shows only that at least3 bases are needed.

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factory floor, the mRNA becomespart of the assembly line. Ribosomes,made of ribosomal RNA (rRNA),clamp onto the mRNA and use itsinformation to assemble the aminoacids in the correct order. The thirdtype of RNA, transfer RNA (tRNA)

is the supplier. Transfer RNA trans-ports amino acids to the ribosome tobe assembled into a protein.

TranscriptionHow does the information in DNA,

which is found in the nucleus, moveto the ribosomes in the cytoplasm?Messenger RNA carries this informa-tion from the DNA to the cell’s ribo-somes for manufacturing proteins,just as a worker brings informationfrom the engineers to the factoryfloor for manufacturing a car. In thenucleus, enzymes make an RNA copyof a portion of a DNA strand in aprocess called transcription (transKRIHP shun). Follow the steps inFigure 11.6 as you read about tran-scription.

The process of transcription issimilar to that of DNA replication.

296 DNA AND GENES

Figure 11.6Messenger RNA is madeduring the process oftranscription.

When the process ofbase pairing is com-pleted, the mRNAmolecule breaksaway as the DNAstrands rejoin. ThemRNA leaves thenucleus and entersthe cytoplasm.

CC

As the DNA molecule unzips, free RNA nucleotides pair with complemen-tary DNA nucleotideson one of the DNAstrands. Thus, if asequence of bases on theDNA strand were AGCTAA CCG, the sequence ofbases on the RNA strandwould be UCG AUU GGC.

BB

DNAstrand

DNAstrand

RNAstrand

RNAstrand

A

A

A

T

T

U U

G

G G

G

G

C

C

C

C

The process of tran-scription begins asenzymes unzip themolecule of DNA,just as they do dur-ing DNA replication.

AA

296


Internet Address Book

Note Internet addresses that you find useful in the spacebelow for quick reference.


Learning DisabledA memory device, “You are single,” canhelp students differentiate RNA fromDNA. “You” stands for “U”; RNA hasuracil. “Are” is for “R”; RNA has ribosesugar. Single refers to RNA being singlestranded.

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Animation: TranscriptionDisc 2


DNA Transcription (Ch.32)Disc 1, Side 1, 55 sec.

!:@É"

EnrichmentIntrapersonal Scientists havedeveloped a technique that

uses fluorescence microscopes tofilm DNA. The techniqueinvolves attaching a fluorescentdye to DNA to form a complexthat glows. Then, just as you canwatch a firefly travel across theyard, researchers can follow theDNA and its movements.Scientists are using this methodto investigate how chromosomalDNA is tightly bound to histonesand other proteins and how theyfold into their functional forms.Have interested students investi-gate this technique and proposeother possible uses for it. L3

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The BioLab at theend of the chaptercan be used at thispoint in the lesson.

INVESTIGATEINVESTIGATE

Knowledge Ask students to deter-mine which letter in the sequence of three ismost important in coding for a specificamino acid. Have them give specific exam-ples while referring to Table 11.2. Use thePerformance Task Assessment List forAnalyzing the Data in PASC, p. 27. L2

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Basic Concepts Trans-parency 17 and Master

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296 DNA AND GENES

Transcribe and Translate Molecules of DNA carry thegenetic instructions for protein formation. Converting theseDNA instructions into proteins requires a series of coordi-nated steps in transcription and translation.

Procedure! Copy the data table.@ Complete column B by writing the correct mRNA codon

for each sequence of DNA bases listed in the columnmarked DNA Base Sequence. Use the letters A, U, C, or G.

# Identify the process responsible by writing its name on thearrow in column A.

$ Complete column D by writing the correct anticodon thatbonds to each codon from column B.

% Identify the process responsible by writing its name on the arrow in column C.

^ Complete column E by writing the name of the correctamino acid that is coded by each base sequence. Use Table 11.2 on page 298 to translate the mRNA basesequences to amino acids.

Analysis1. Where within the cell:

a. are the DNA instructions located?b. does transcription occur?c. does translation occur?

2. Describe the structure of a tRNA molecule. 3. Explain why specific base pairing is essential to the

processes of transcription and translation.

MiniLab 11-1MiniLab 11-1 Predicting planet in our solar system. With pro-teins, as in software, elaborate thingsare constructed from a simple code.

Translation: FrommRNA to Protein

How is the language of mRNAtranslated into the language of pro-teins? The process of converting theinformation in a sequence of nitro-gen bases in mRNA into a sequenceof amino acids that make up a proteinis known as translation. You cansummarize transcription and transla-tion by completing the MiniLab.

Translation takes place at the ribo-somes in the cytoplasm. In prokary-otic cells that have no nucleus, themRNA is made in the cytoplasm. Ineukaryotic cells, mRNA leaves thenucleus through an opening in thenuclear membrane and travels to thecytoplasm. When the strands ofmRNA arrive in the cytoplasm, ribo-somes attach to them like clothespinsclamped onto a clothesline.

The role of transfer RNAFor proteins to be built, the 20 dif-

ferent amino acids dissolved in thecytoplasm must be brought to theribosomes. This is the role of transferRNA (tRNA), Figure 11.7. Each


T

Anticodon

Aminoacid

Chain of RNAnucleotides

ransfer RNAmolecule

AA

U A C

Figure 11.7A tRNA molecule is composed of about 80 nucleotides.Each tRNA recognizes only one amino acid. The aminoacid becomes bonded to one side of the tRNA molecule.Located on the other side of the tRNA molecule arethree nitrogen bases, called an anticodon, that pair upwith an mRNA codon during translation.

DNA basesequence

D

tRNA anticodon

C

Process

B

mRNAcodon

A

Process

AAT

GGG

ATA

AAA

GTT

E

Amino acid

→

→

→

→

→

→

→

→

→

→

Data Table

299

PurposeStudents will follow a series ofDNA base codes through tran-scription and translation.

Process Skillsapply concepts, analyze informa-tion, compare and contrast, drawa conclusion

Teaching Strategies■ Make sure that students haveread and reviewed the section inthe text dealing with transcriptionand translation before attemptingthis activity.■ If you feel it is necessary, youmay want to walk studentsthrough the first example.

Expected ResultsSee the table below.

Analysis1. a. on chromosomes in the

nucleusb. in the nucleusc. in the ribosomes

2. tRNA is a small moleculethat has a three-base anti-codon at one end and anamino-acid attachment site atthe opposite end.

3. Precise base pairing is essen-tial to transcription andtranslation so that the correctgenetic information in DNAis transferred to the formingprotein.

Skill Provide students witha series of amino acids and havethem make a poster, workingbackwards from these amino acidsto the tRNA anticodon to themRNA codon to DNA. Use thePerformance Task AssessmentList for Poster in PASC, p. 73.


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MiniLab 11-1MiniLab 11-1when a sequence of three bases isused; thus, 64 different mRNAcodons are in the genetic code,shown in Table 11.2. Some codonsdo not code for amino acids; theyprovide instructions for assemblingthe protein. For example, UAA is astop codon indicating that proteinproduction ends at that point. AUGis a start codon as well as the codonfor the amino acid methionine. Asyou can see, more than one codoncan code for the same amino acid.However, for any one codon, therecan be only one amino acid.

All organisms use the same geneticcode for amino acids and assemblingproteins; UAC codes for tyrosine inthe messenger RNA of bacteria, birchtrees, and bison. For this reason, thegenetic code is said to be universal,and this provides evidence that all lifeon Earth evolved from a commonorigin. From the chlorophyll of a

birch tree to the digestive enzymes ofa bison, a large number of proteinsare produced from DNA. It may behard to imagine that only fournucleotides can produce so manydiverse proteins; yet, think aboutcomputer programming. You mayhave seen computer code, such as00010101110000110. Through abinary language with only twooptions—zeros and ones—manytypes of software are created. Fromcomputer games to World WideWeb browsers, complex software isbuilt by stringing together the zerosand ones of computer code into longchains. Likewise, complex proteinsare built from the long chains ofDNA carrying the genetic code. Ifthe DNA in all the human cells of anadult were lined up end-to-end, itwould stretch to about 60 billionmiles—about 16 times the distancefrom the sun to Pluto, the outermost

298 DNA AND GENES

U

C

A

G

Second letter

U

Phenylalanine (UUU)

Phenylalanine (UUC)

Leucine (UUA)

Leucine (UUG)

Leucine (CUU)

Leucine (CUC)

Leucine (CUA)

Leucine (CUG)

Isoleucine (AUU)

Isoleucine (AUC)

Isoleucine (AUA)

Methionine;Start (UAG)

Valine (GUU)

Valine (GUC)

Valine (GUA)

Valine (GUG)

C

Serine (UCU)

Serine (UCC)

Serine (UCA)

Serine (UCG)

Proline (CCU)

Proline (CCC)

Proline (CCA)

Proline (CCG)

Threonine (ACU)

Threonine (ACC)

Threonine (ACA)

Threonine (ACG)

Alanine (GCU)

Alanine (GCC)

Alanine (GCA)

Alanine (GCG)

A

Tyrosine (UAU)

Tyrosine (UAC)

Stop (UAA)

Stop (UAG)

Histadine (CAU)

Histadine (CAC)

Glutamine (CAA)

Glutamine (CAG)

Asparagine (AAU)

Asparagine (AAC)

Lysine (AAA)

Lysine (AAG)

Aspartate (GAU)

Aspartate (GAC)

Glutamate (GAA)

Glutamate (GAG)

G

Cysteine (UGU)

Cysteine (UGC)

Stop (UGA)

Tryptophan (UGG)

Arginine (CGU)

Arginine (CGC)

Arginine (CGA)

Arginine (CGG)

Serine (AGU)

Serine (AGC)

Arginine (AGA)

Arginine (AGG)

Glycine (GGU)

Glycine (GGC)

Glycine (GGA)

Glycine (GGG)

Firstletter

Third letter

U

C

A

G

U

C

A

G

U

C

A

G

U

C

A

G

Table 11.2 The messenger RNA genetic code

OriginWORDWORD

codon From the Latinword codex, meaning“a tablet for writ-ing.” A codon is thethree-nucleotidesequence that codesfor an amino acid.

298

ReinforcementVisual-Spatial Give studentsa blank four square by four

square bingo card. Students writeone amino acid into each square.An amino acid should be usedonly once. Play bingo, but don’tcall out amino acids; instead, pickand call mRNA codons. Forexample, if you call UCU, stu-dents use Table 11.2 and crossout serine on their cards.

DiscussionHave students compare the num-ber of letters in the alphabet withthe number of amino acids avail-able for protein formation. Howmany different words can bemade using 26 letters? Howmany different proteins can bemade with the amino acids avail-able? Ask students to considerthat proteins contain many moreamino acids than words do let-ters. L2

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MMEETING EETING IINDIVIDUAL NDIVIDUAL NNEEDS EEDS MEETING INDIVIDUAL NEEDS

Visually ImpairedKinesthetic Help visually impaired stu-dents understand Problem-Solving Lab

11-2 by having them manipulate combina-tion locks. Then make large copies of thesafe diagrams. L1

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Converting LanguagesLinguistic Translation is a term thatis used for converting words in one

language to words in a different lan-guage. Have students write hypothesesfor why the process of converting a basesequence in mRNA to an amino acidsequence in a protein is also called transla-tion.

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DNA basesequence

D

tRNA anticodon

C

Process

B

mRNAcodon

A

Process

AAT

GGG

ATA

AAA

GTT

transcription

transcription

transcription

transcription

transcription

UUA

CCC

UAU

UUU

CAA

AAU

GGG

AUA

AAA

GUU

translation

translation

translation

translation

translation

leucine

proline

tyrosine

phenylalanine

glutamine

E

Amino acid

Data Table


Translation (Ch. 33)Disc 1, Side 11 min. 29 sec.!:JÑ"


BioLab and MiniLab Work-sheets, pp. 49-50

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Reteaching SkillsTransparency 18 andMaster

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Understanding Main Ideas1. In what ways do the chemical structures of DNA

and RNA differ?2. What is a codon, and what does it represent?3. What is the role of tRNA in protein synthesis?4. Compare and contrast the final products of DNA

replication and transcription.

Thinking Critically5. You have learned that there is a stop codon that

signals the end of an amino acid chain. Why is itimportant that a signal to stop translation bepart of protein synthesis?

6. Sequencing Sequence the steps involved inprotein synthesis from the production of mRNAto the final translation of the DNA code. Formore help, refer to Organizing Information inthe Skill Handbook.


Usually, the first codon on mRNA is AUG, whichcodes for the amino acid methionine. AUG signalsthe start of protein synthesis. When this signal isgiven, the ribosome slides along the mRNA to thenext codon.

BB A new tRNA molecule carrying an amino acidpairs with the second mRNA codon.

CC

When the first and second amino acids are inplace, an enzyme joins them by forming a peptidebond between them.

DD As the process continues, a chain of amino acids isformed until the ribosome reaches a stop codonon the mRNA strand.

EE

Methionine

AUGA

A

U

U

G AAG U GCUC

C

C A A

tRNA anticodon

AUGA U G AAG

G

U

U

GCUC

C

C A A

Alanine

U AC

AUGA U G AAG

G

U

U

GCUC

C

C A A

Alanine

Peptidebond

Methionine

AA

A A

U UGA U G AAG UU

C

C

C A A

Stopcodon

ReteachVisual-Spatial On the chalk-board, illustrate the pro-

cesses of transcription andtranslation of a particular portionof a DNA strand. Have studentscopy the diagram and label eachprocess. Then have them checkeach other’s papers.

ExtensionKinesthetic Have studentsresearch the structure and

function of histone molecules.They could build a model of theeukaryotic chromosome. “Simu-lating the Eukaryotic Chromo-some” by Leo E. Spencer, Journalof College Science Teaching, May1985, may be helpful.

Knowledge Have studentsexplain how they would be able toidentify the complementary com-ponents of a strand of DNA ormRNA if given the componentsof one strand.

4 CloseUsing a TableAsk students what would happento a protein if one base werechanged in the DNA that codesfor it. Use Table 11.2 to demon-strate to students what wouldoccur if CAT were changed toCTT. Discuss what changing oneamino acid might do to proteinstructure. This discussion willserve as a lead-in to the next sec-tion.

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tRNA molecule attaches to only onetype of amino acid.

Correct translation of the mRNAmessage depends upon the joining ofeach mRNA codon with the correcttRNA molecule. How does a tRNAmolecule carrying its amino acid rec-ognize which codon to attach to?The answer again involves base pair-ing. On the opposite side of thetransfer-RNA molecule from theamino-acid attachment site, there is asequence of three nucleotides thatare the complement of the nucleotidesin the codon. These three nucleotidesare called an anticodon because theybond to the codon of the messengerRNA. The tRNA carries only theamino acid that the anticodon speci-fies. For example, one tRNA mole-cule for the amino acid cysteine hasan anticodon of A-C-A. This anti-codon bonds with the mRNA codonU-G-U. Now, use Table 11.2 to findthe mRNA codon for tryptophan,then determine its tRNA anticodon.

Translating the mRNA codeFollow the steps in Figure 11.8 as

you read how translation occurs. Astranslation begins, a tRNA moleculebrings the first amino acid to themRNA strand that is attached to theribosome, Figure 11.8A. The anti-codon forms a temporary bond with

the codon of the mRNA strand,Figure 11.8B. This places the aminoacid in the correct position for form-ing a bond with the next amino acid.The ribosome slides down themRNA chain to the next codon, anda new tRNA molecule brings anotheramino acid, Figure 11.8C . Theamino acids bond, the first tRNAreleases its amino acid and detachesfrom the mRNA, Figure 11.8D. ThetRNA molecule is now free to pickup and deliver another molecule ofits specific amino acid to a ribosome.Again, the ribosome slides down tothe next codon; a new tRNA mole-cule arrives, and its amino acid bondsto the previous one. A chain of aminoacids begins to form. When a stopcodon is reached, translation ends,and the amino acid strand is releasedfrom the ribosome, Figure 11.8E.

Like Silly String sprayed into afriend’s hair, amino acid chainsbecome proteins when they are freedfrom the ribosome and twist and curlinto complex three-dimensionalshapes. Unlike Silly String, however,each protein chain forms the sameshape every time it is produced.These proteins become enzymes andcell and tissue structures. The forma-tion of protein, originating from theDNA code, produces the diverse andmagnificent living world.

300 DNA AND GENES

Figure 11.8A protein is formedby the process oftranslation.

As translation begins, thestarting end of the mRNAstrand attaches to a ribo-some. Then, tRNA mole-cules, each carrying a spe-cific amino acid, approachthe ribosome. When atRNA anticodon pairs withthe first mRNA codon, thetwo molecules temporarilyjoin together.

AA

AUGA U G AAG U GCUC C A A

mRNA codon

Ribosome

300

Knowledge On the chalk-board, write the sequence for onestrand of DNA. Have studentscopy the sequence and write thecorresponding sequences formRNA, the tRNA anticodons,and the coded protein. Studentsshould follow the changes in logi-cal steps from the original DNAthrough transcription and transla-tion. Afterward, go through thecorrect answer on the board.

3 AssessCheck for UnderstandingReview the processes of tran-scription and translation orally.Ask students to supply missingwords, descriptions, and processwords, including DNA, comple-mentary codons, mRNA, tRNA,ribosomal RNA, transcription,translation, and anticodons.Discuss the definitions. L1

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PortfolioPortfolio

TranslationLinguistic Have students write asummary of the events that are

being shown in Figure 11.8. Have theminclude the events that led up to and thatwill follow translation.

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P R O J E C TBuilding a Model

Kinesthetic Have students build amodel demonstrating protein syn-

thesis. They may wish to use various typesof macaroni on poster board, coloredpipe cleaners, beads, colored buildingblocks, or yarn.

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BioQuest: Building a ProteinDisc 2Animation: TranslationDisc 2

Section AssessmentSection AssessmentSection Assessment1. RNA contains ribose and uracil and

DNA contains deoxyribose andthymine. RNA is usually single stranded.

2. A codon is a 3-base sequence of mRNAthat codes for a single amino acid.

3. Transfer RNA brings a specific aminoacid to a ribosome by matching acodon on the messenger RNA strand.

4. Replication produces 2 molecules of

double-stranded DNA. Transcriptionresults in the production of 1 moleculeof single-stranded RNA.

5. Because a protein’s 3-dimensionalstructure depends on its length as wellas its amino acid sequence, translationmust start and stop at precise positions.

6. The DNA strands separate and freeRNA nucleotides pair with complemen-

tary DNA bases on one of the DNAstrands, forming mRNA. mRNA leavesthe nucleus and attaches to a ribo-some. tRNA molecules, carrying spe-cific amino acids, pair with theappropriate mRNA codons. When 2amino acids are in place, an enzymejoins them together.

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Reinforcement and StudyGuide, pp. 48-49

Content Mastery, p. 55 L1

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CAREERS IN BIOLOGY

Genetic Counselor

A re you fascinated by howyou inherit traits from your

parents? If so, you couldbecome a genetic counselorand help people assess theirrisk of inheriting or passing ongenetic disorders.

Skills for the JobGenetic counselors are medical

professionals who work on a healthcare team. They analyze families’ medicalhistories to determine their risk of having children withgenetic disorders, such as hemophilia or cystic fibrosis.Counselors also educate the public and help families withgenetic disorders find support and treatment. These coun-selors may work in a medical center, a private practice,research, or a commercial laboratory. To become a counselor,you must earn a two-year master’s degree in medical geneticsand pass a test to become certified. The most importantrequirement is the ability to listen and to help families makedifficult decisions.

For more careers in related fields, be sureto check the Glencoe Science Web Site.

www.glencoe.com/sec/science

resulting protein is nonfunctional,and the embryo does not survive.

In some rare cases, a gene muta-tion may have positive effects. Anorganism may receive a mutation thatmakes it faster or stronger; such amutation may help an organism—and its offspring—better survive inits environment. You will learn laterthat mutations that benefit a speciesplay an important role in the evolu-tion of that species.

Mutations in body cellsWhat happens if powerful radia-

tion, such as gamma radiation, hitsthe DNA of a nonreproductive cell, acell of the body such as in skin, mus-cle, or bone? If the cell’s DNA ischanged, this mutation would not bepassed on to offspring. However, themutation may cause problems for theindividual. Damage to a gene mayimpair the function of the cell; forexample, it may make a muscle celllose its ability to make a protein thatcontracts, or a skin cell may lose itselasticity. When that cell divides, the

11.3 GENETIC CHANGES 303

Figure 11.9Nuclear power plant workerswear radiation badges (a) andpocket dosimeters (b) to monitortheir exposure to radiation.

a

b

303

2 TeachConcept DevelopmentIt may be hard to think of blue eyecolor in humans as a mutation,but it is. Discuss disadvantagesand advantages of this mutation toan individual. Disadvantage is thatit makes eyes more sensitive to sun-light. Advantage is that many peoplefind them attractive.

EnrichmentLogical-Mathematical Askstudents which scenario is

worse as a result of DNA damageby radiation to a body cell: (a) thefunction of the cell is altered butthe cell survives, or (b) the celldies. Probably (a) is a worse out-come. When the cell dies, others cantake its place. When it has DNAdamage, all new cells that come fromthis cell will contain the same defects.L3

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Career PathCourses in high school:biology, psychology, and

communicationCollege: bachelor’s degree inbiology, genetics, nursing, publichealth, social work, or psychol-ogy; master’s degree in medicalgenetics

Career IssueAsk students whether geneticcounselors should only give fami-lies information about theirgenetic background, or shouldthey try to influence the families’decisions about having children.Have them give reasons for theiranswer.

For More InformationFor more information aboutbecoming a genetic counselor,write to:

National Society of GeneticCounselors

c/o Bea Leopold233 Canterbury DriveWallingford, PA 19086-6617

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Section

302 DNA AND GENES

Mutation: A Change in DNA

Radiation may be given off in thereactor areas of nuclear power plants.If a person is exposed to this radia-tion, serious problems may result.For this reason, nuclear power plantworkers wear radiation-detectingdevices such as the ones shown inFigure 11.9. These devices allowworkers to monitor and limit theirexposure to radiation. Powerfulforms of radiation, such as thegamma radiation of nuclear reac-tions, can break apart molecules. If agamma ray hits a molecule of DNA,the nucleotide sequence may bechanged. As you know, the sequences

of nucleotides in DNA moleculescontrol the structure and function ofcells. Any change in the DNAsequence is called a mutation.

Mutations in reproductive cellsMutations affect the reproductive

cells of an organism by changing thesequence of nucleotides within a genein a sperm or an egg cell. If thesecells take part in fertilization, thechanged gene would be part of thegenetic makeup of the offspring. Themutation may produce a new trait orit may result in a protein that doesnot work correctly, resulting in struc-tural or functional problems in cellsand in the organism. Sometimes, themutation is so severe that the

DNA controls the structures and functions of a cell. Whathappens when the sequence of

DNA nucleotides is changed in a gene?Sometimes it may have little or noharmful effect, as in this tailless Manxcat, and the DNA changes are passedon to offspring of the organism. Atother times, however, the changecan cause the cell to behavedifferently. For example, inthe type of skin cancershown here, UV rays fromthe sun change the DNAand cause the cells to growand divide rapidly.

SECTION PREVIEW

ObjectivesCategorize the differ-ent kinds of mutationsthat can occur in DNA.Compare the effects of different kinds ofmutations on cells andorganisms.

Vocabularymutationpoint mutationframeshift mutationchromosomal mutationmutagen

11.3 Genetic Changes

Manx cat (above)and melanoma(inset)

OriginWORDWORD

mutation From the Latinword mutare, mean-ing “to change.”Mutations arechanges in DNA.

302

Section 11.3

PrepareKey ConceptsMutations are changes in thesequence of DNA. Their effecton body cells is different than onreproductive cells. The causesand results of gene and chromo-some mutations are discussed.The section ends with a discus-sion of DNA repair mechanisms.

Planning■ Make copies of Figures 11.10

and 11.11 without captions forthe Reteach.

■ Gather a coiled telephone cordand twist ties for the QuickDemo.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 28 on the overhead pro-jector and have the studentsanswer the accompanying ques-tions.

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A G G G GA

A A

C

A A

C U U U U U U U U U

A A A

C

CU

A

GU

G

UA

UU

C

mRNAStop codon

tRNA


What would be the resulting sequence of amino acids in this growingprotein chain, based on the sequence of bases in the illustrated messenger RNA?

Why is this exact base sequence important?

11

22

SECTION FOCUS

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Transparency Nitrogen BaseSequence28


MutationsLinguistic Ask students to describein their journals the images that the

word mutation conjures up in their minds.They may describe fantastic beings theyhave encountered in movies and stories.Point out that real mutations are usuallymuch less spectacular.

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CAREERS IN BIOLOGY

Day in the Life of a GeneticCounselor

Interpersonal Have students find thenames and phone numbers of genetic

counselors. In pairs or groups, they should

make an appointment to interview a coun-selor. Students should make a list of types ofclients who visited the counselor on one par-ticular day. Analyze the results as a class. L2

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Resource ManagerResource ManagerSection Focus Transparency 28 and

MasterLaboratory Manual, pp. 79-82 L2

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What type of mutation results in sickle-cell anemia?A condition called sickle-cell anemia results from a geneticchange in the base sequence of DNA. Red blood cells inpatients with sickle-cell anemia have molecules of hemoglo-bin that are misshapen. As a result of this change in proteinshape, sickled blood cells clog capillaries and prevent normalflow of blood to body tissues, causing severe pain.

AnalysisTable 11.3 shows the sequence of bases in a short seg-

ment of the DNA that controls the order of amino acids inthe protein, hemoglobin.

Thinking Critically1. Use Table 11.2 on page 298 to transcribe and translate the

DNA base sequence for normal hemoglobin and for sick-led hemoglobin into amino acids. Remember that thetable lists mRNA codons, not DNA base sequences.

2. Does this genetic change illustrate a point mutation orframeshift mutation? Explain your answer.

3. Explain why the correct sequence of DNA bases is impor-tant to normal development of proteins.

4. Assume that the base sequence reads GGG CTT CTT AAAinstead of the normal sequence for hemoglobin. Wouldthis result in sickled hemoglobin? Explain your answer.

Problem-Solving Lab 11-3Problem-Solving Lab 11-3 Making and Using Tables

Frameshift mutationsWhen the mRNA strand moves

across the ribosome, a new amino acidis added to the protein for every codonon the mRNA strand. What wouldhappen if a single base were lost from aDNA strand? This new sequence withthe deleted base would be transcribedinto mRNA. But then, the mRNAwould be out of position by one base.As a result, every codon after thedeleted base would be different, asshown in Figure 11.10B. This muta-tion would cause nearly every aminoacid in the protein after the deletion tobe changed. In the sentence THEDOG BIT THE CAT, deleting a Gwould produce the sentence THEDOB ITT HEC AT. The same effectwould also result from the addition ofa single base. A mutation in which asingle base is added or deleted fromDNA is called a frameshift mutationbecause it shifts the reading of codonsby one base. In general, point muta-tions are less harmful to an organismbecause they disrupt only a singlecodon. The MiniLab on the next pagewill help you distinguish point muta-tions from frameshift mutations, andthe Problem-Solving Lab on this pagewill show you an example of an actualhuman mutation.

ChromosomalMutations

Changes may occur at the level ofchromosomes as well as in genes.Mutations to chromosomes may occurin a variety of ways. For example,sometimes parts of chromosomes arebroken off and lost during mitosis ormeiosis. Often, chromosomes breakand then rejoin incorrectly.Sometimes, the parts join backwardsor even join to the wrong chromo-some. These changes in chromosomesare called chromosomal mutations.

Effects of chromosomal mutations

Chromosomal mutations occur inall living organisms, but they areespecially common in plants. Suchmutations affect the distribution ofgenes to gametes during meiosisbecause they cause nondisjunction,the failure of chromosomes to sepa-rate. Nondisjunction occurs becausehomologous chromosomes cannotpair correctly when one has extra ormissing parts. Gametes that shouldhave a complete set of genes may endup with extra copies or a completelack of some genes.


Normal hemoglobin

Sickled hemoglobin

GGG CTT CTT TTT

GGG CAT CTT TTT

Table 11.3 DNA base sequences

305

PurposeStudents will compare the basesequence of a segment of normalDNA with the base sequence ofDNA that codes for sickledhuman hemoglobin.

Process Skillsanalyze information, apply con-cepts, compare and contrast, rec-ognize cause and effect

Teaching Strategies■ Make sure that students arefamiliar with Table 11.2 andunderstand how it is to be used.■ Discuss sickle-cell anemiabriefly and point out its greateroccurrence among African Amer-icans.

Thinking Critically

1. normal: proline, glutamate,glutamate, lysine; sickled:proline, valine, glutamate,lysine

2. Point mutation; one codonhas been altered and oneamino acid is different.

3. In this example, the correctsequence of amino acids isneeded to form a molecule ofnormal hemoglobin. With achange of only one aminoacid, the protein molecule nolonger functions in a normalmanner.

4. Student answers may vary.Probably not; protein forma-tion is very specific and thesubstitution of a differentamino acid could result in atotally different form ofhemoglobin.

Performance Ask studentsto write an informative newspaperarticle in which they describesickle-cell anemia and explain itscause to the public. Use thePerformance Task AssessmentList for Newspaper Article inPASC, p. 69. L2

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304

ReinforcementLogical-Mathematical Havestudents write a sequence of

twelve mRNA nucleotides. Thesequence should be exchangedwith a classmate, who will writethe protein strand produced andreturn the sequence to the firststudent to check. Now the firststudent changes one nucleotideto simulate a point mutation.Students should repeat theexchanges.

Performance Have stu-dents make a concept map formutations. The map should in-clude mutagens, gene and chro-mosome mutations, and the typesof each. L2

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Use a coiled telephone cord and twist ties to show studentshow the three-dimensionalshape of a protein can changewhen a single amino acid ischanged in a point mutation.The twist ties can representcross linkages between certainamino acids such as cysteine.P

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Learning DisabledVisual-Spatial Help students under-stand the differences between a

gene mutation and a chromosomal muta-tion by asking them to draw examples onthe chalkboard. A gene mutation affectsone trait, but a chromosomal mutationaffects many traits.

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VIDEOTAPEThe Secret of Life

It’s in the Genes: EvolutionCD-ROMBiology: The Dynamics of LifeExploration: Mutations

Disc 2


Reteaching Skills Trans-parency 19a, 19b andMasters

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Internet Address Book

Note Internet addressesthat you find useful in

the space below for quick reference.

PortfolioPortfolio

Protein Building Linguistic Have students write anessay comparing the building of

proteins to the building of a house andwhat will occur if there are problems withthe blueprint guiding the builders.P

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new cells also will have the samemutation. Many scientists suggestthat the buildup of cells with lessthan optimal functioning is animportant cause of aging.

Some mutations of DNA in bodycells affect genes that control celldivision. This can result in the cellsgrowing and dividing rapidly, pro-ducing the disease called cancer. Asyou learned earlier, cancer is theuncontrolled dividing of cells.Cancer may result from gene muta-tions. For example, ultraviolet radia-tion in sunlight can change the DNAin skin cells, altering their behavior.The cells reproduce rapidly, causingskin cancer.

The effects of point mutationsConsider what might happen if an

incorrect amino acid were insertedinto a growing protein chain during

the process of translation. The mis-take might affect the structure of theentire molecule. Such a problem canoccur if a point mutation arises. Apoint mutation is a change in a sin-gle base pair in DNA.

A simple analogy can illustratepoint mutations. Read the two sen-tences below to see what happenswhen a single letter in the first sen-tence is changed.

THE DOG BIT THE CAT.THE DOG BIT THE CAR.

As you can see, changing a singleletter changes the meaning of theabove sentence. Similarly, a change ina single nitrogen base can change theentire structure of a protein becausea change in a single amino acid canaffect the shape of the protein.Figure 11.10A shows what can hap-pen with a point mutation.

304 DNA AND GENES

Figure 11.10The results of a pointmutation and aframeshift mutationare different. The dia-grams show themRNA that would beformed from eachcorresponding DNA.

Proteins that are produced as a result of frameshift mutations seldom functionproperly because such mutations usually change many amino acids. Adding ordeleting one base of a DNA molecule will change nearly every amino acid in theprotein after the addition or deletion.

BB

In this point mutation, the mRNA produced by the mutated DNA had the base gua-nine changed to adenine. This change in the codon caused the insertion of serinerather than glycine into the growing amino acid chain. The error may or may notinterfere with protein function.

AA

Normal

Pointmutation

Frameshiftmutation

. . .

. . .

AC AUGUGA U G A A G U U U G G C U AmRNA

StopMet Lys Phe Gly Ala LeuProtein

mRNA

StopMet Lys Phe Ser Ala LeuProtein

A AC UGUGA U G A A G U U U U AG C

Replace G with A

A

mRNA

Met Lys Leu Ala His CysProtein

G AC AAUGUGA U G A G U U G C U

UDeletion of U

A

Forms of radiation, such as X rays,cosmic rays, ultraviolet light, andnuclear radiation, are dangerousmutagens because they contain alarge amount of energy that can blastDNA apart. The breaking andreforming of a double-stranded DNAmolecule can result in deletions.Radiation can also cause substitutionsof incorrect nucleotides in the DNA.

Chemical mutagens include diox-ins, asbestos, benzene, cyanide, andformaldehyde, compounds that arecommonly found in buildings and inthe environment, Figure 11.12.These mutagens are highly reactivecompounds that interact with theDNA molecule and cause changes.Chemical mutagens usually result ina substitution mutation.

Repairing DNAThe cell processes that copy

genetic material and pass it from onegeneration to the next are usuallyaccurate. This accuracy is importantto ensure the genetic continuity ofboth new cells and offspring. Yet,mistakes sometimes do occur. Thereare many sources of mutagens in anorganism’s environment. Althoughmany of these are due to humanactivities, others—such as cosmic

rays from outer space—have affectedliving things since the beginning oflife. Repair mechanisms that fixmutations in cells have evolved.Much like a book editor, enzymesproofread the DNA and replaceincorrect nucleotides with correctnucleotides. These repair mecha-nisms work extremely well, but theyare not perfect. The greater theexposure to a mutagen such as UVlight, the more likely is the chancethat a mistake will not be corrected.Thus, it is wise for people to limittheir exposure to mutagens.


Figure 11.12Asbestos was for-merly used to insu-late buildings. It isnow known to causelung cancer andother lung diseasesand must beremoved from thesebuildings, as shownhere.


Understanding Main Ideas1. What is a mutation?2. Describe how point mutations and frameshift

mutations affect the synthesis of proteins.3. Describe why a mutation of a sperm or egg cell

has different consequences than a mutation of aheart cell.

4. What is the relationship between mutations andcancer?

Thinking Critically5. Why do you think low levels of mutation might

be an adaptive advantage to a species, whereashigh levels of mutation might be a disadvantage?

6. Recognizing Cause and Effect In an experi-ment with rats, the treatment group receivesradiation while the control group does not.Months later, the treatment group has a greaterpercentage of rats with cancer and newborn ratswith birth defects than the control group.Explain these observations. For more help, referto Thinking Critically in the Skill Handbook.


3 AssessCheck for UnderstandingAsk students to name the type ofmutation involved in each of thefollowing cases. (a) One kind ofbase in DNA takes the place ofanother. (b) Some genes areduplicated on the same chromo-some. (c) Part of one chromo-some breaks off and is attached toa different one. (a) point mutation,(b) insertion, (c) translocation

Reteach Use an overhead projector toshow Figures 11.10 and 11.11without captions. Have studentsdescribe in their own words whatis taking place in each type ofmutation.

ExtensionAsk students to research poly-ploidy in plants and find out theeffects of extra sets of chromo-somes on plants.

Knowledge Ask studentsto explain the effects of point,frameshift, and chromosomalmutations.

4 CloseDiscussionHave each student form ahypothesis about how mutationsmay be involved in evolution of aspecies. Discuss the hypotheses asa class. Correct any misconcep-tions students may have. L2

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A B C D E F G H A B C E F G H

A B C D E F G H A B C B C D E F G H

A B C D E F G H A D C B E F G H

A B C D E F G H W X A B C D E F G H

TranslocationW X Y Z Y Z

Deletion

Insertion

Inversion

Gene Mutations and Proteins Genemutations often have serious effects onproteins. In this activity, you will demon-strate how such mutations affect proteinsynthesis.

Procedure! Copy the following base sequence of one strand of an

imaginary DNA molecule: AATGCCAGTGGTTCGCAC.@ Then, write the base sequence for an mRNA strand that

would be transcribed from the given DNA sequence.# Use Table 11.2 to determine the sequence of amino acids

in the resulting protein fragment.$ If the fourth base in the original DNA strand were

changed from G to C, how would this affect the resultingprotein fragment?

% If a G were added to the original DNA strand after thethird base, what would the resulting mRNA look like?How would this addition affect the protein?

Analysis1. Which change in DNA was a point mutation? Which was a

frameshift mutation?2. In what way did the point mutation affect the protein?3. How did the frameshift mutation affect the protein?

MiniLab 11-2MiniLab 11-2Few chromosome mutations are

passed on to the next generationbecause the zygote usually dies. Incases where the zygote lives anddevelops, the mature organism isoften sterile and thus incapable ofproducing offspring. The mostimportant of these mutations—dele-tions, insertions, inversions, andtranslocations—are illustrated inFigure 11.11.

Causes of MutationsSome mutations seem to just hap-

pen, perhaps as a mistake in basepairing during DNA replication.These mutations are said to be spon-taneous. However, many mutationsare caused by factors in the environ-ment. As you learned earlier, gammaradiation is capable of causing muta-tions. Any agent that can cause achange in DNA is called a mutagen(MYEWT uh jun). Mutagens includehigh energy radiation, chemicals, andeven high temperatures.

306 DNA AND GENES

DNA segment

Figure 11.11Study the four kinds of chromosomal mutations.

Deletions occur when part of achromosome is left out.

AA

Insertions occur when a part of achromatid breaks off andattaches to its sister chromatid.The result is a duplication ofgenes on the same chromosome.

BB

Inversions occur when part of achromosome breaks off and isreinserted backwards.

CC

Translocations occur when part ofone chromosome breaks off and isadded to a different chromosome.

DD

Making andUsing Tables

306

Purpose Students will examine the effectof gene mutations on proteins.

Process Skillsrecognize cause and effect, ana-lyze

Teaching Strategies■ Individual students can do thisMiniLab at their desks as youwalk around the room and checktheir work.

Expected ResultsBase sequence of mRNA:UUACGGUCACCAAGCGUG;amino acids: leucine-arginine-serine-proline-serine-valine;Changing the fourth base in theDNA from G to C would changethe second amino acid from argi-nine to glycine. Adding G at thefourth position of the DNAwould result in the mRNA basesequence UUACCGGUCAC-CAAGCGUG and the aminoacid sequence leucine-proline-valine-threonine-lysine-arginine.

Analysis1. Changing G to C was a point

mutation; adding G to thechain was a frameshift muta-tion.

2. The point mutation changedonly one amino acid.

3. The frameshift mutationchanged every amino acidfollowing the addition of G.

Performance Ask studentsto give an oral presentationexplaining the effect on the aminoacid sequence if a C is substitutedfor a T in the third position of theDNA strand above. The aminoacid sequence will be the samebecause both sequences code forleucine. Use the Performance TaskAssessment List for Oral Presen-tation in PASC, p. 71 L1

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MiniLab 11-2MiniLab 11-2


Mutagens Intrapersonal Have students doresearch on various mutagenic agents

such as X rays, ultraviolet light, radioactivesubstances, and other chemicals. Studentsshould report on the mechanism by whicheach agent causes mutations.

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Section AssessmentSection AssessmentSection Assessment1. A mutation is any mistake or change in

the DNA sequence.2. A point mutation may change a single

amino acid in a protein. A frameshiftmutation may alter every amino acidafter the mutation because the shift inbases occurs all along the strand.

3. A mutation of a reproductive cellaffects the individual’s offspring.

A mutation of a heart cell affects onlythe individual.

4. Mutations of a body cell may causecancer by altering the cell processesthat control cell division. This makesthe cells divide rapidly.

5. A change in the DNA might result in abetter adaptation. A high rate ofmutation could cause rapid speciation

or lead to extinction of a species. A lowlevel of mutations provides stability.

6. Greater incidence of cancer can beexplained by the radiation causingmutations in the processes that controlcell division in body cells. More birthdefects can be explained by mutationsin the reproductive cells.

307

Resource ManagerResource ManagerBioLab and MiniLab Worksheets,

p. 51Reinforcement and Study Guide,

p. 50Content Mastery, pp. 53, 56 L1

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1. Observing and Inferring Doesthe mRNA model more closelyresemble the DNA strand fromwhich it was transcribed or thecomplementary strand that wasn’tused? Explain your answer.

2. Recognizing Cause and EffectExplain how the structure ofDNA enables the molecule to beeasily transcribed. Why is thisimportant for genetic informa-tion?

3. Relating Concepts Why is RNAimportant to the cell? How does

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

1. Copy the illustrations of the fourdifferent DNA nucleotides ontoyour construction paper, makingsure that each differentnucleotide is on a different colorpaper. You should make tencopies of each nucleotide.

2. Using scissors, carefully cut outthe shapes of each nucleotide.

3. Using any order of nucleotidesthat you wish, construct a double-stranded DNA molecule. If youneed more nucleotides, copythem as before.

4. Fasten your molecule togetherusing clear tape. Do not tapeacross base pairs.

5. As in step 1, copy the illustrationsof A, G, and C nucleotides. Usethe same colors of constructionpaper as in step 1. Use the fifthcolor of construction paper tomake copies of uracil nucleotides.

6. With scissors, carefully cut outthe nucleotide shapes.

7. With your DNA molecule in

PROCEDUREPROCEDURE

an mRNA molecule carry infor-mation from DNA?

Going FurtherGoing Further

Biology Journal Do library research tofind out more about how the bases in DNAwere identified and how the base pairingpattern was determined.

To find out more aboutDNA, visit the GlencoeScience Web Site.

www.glencoe.com/sec/science

front of you, demonstrate theprocess of transcription by firstpulling the DNA molecule apartbetween the base pairs.

8. Using only one of the strands ofDNA, begin matching comple-mentary RNA nucleotides with the exposed bases on the DNA model to make mRNA.

9. When you are finished, tape your new mRNA molecule together.


1. mRNA more closely resem-bles the complementaryDNA. They have the samebase sequence except thatmRNA has uracil in place ofthymine.

2. Because DNA is double-stranded, sections can beunzipped to allow comple-mentary bases to hydrogenbond while the remainingDNA stays zipped. Thus,only the information neededat one time is being tran-scribed.

3. The mRNA is formed as acomplementary copy of thegenetic information. TheRNA copy can leave thenucleus while the “mastercopy” stays protected withinthe nucleus.

Portfolio Have studentswrite a lab report summarizingthe lab and including answers toAnalyze and Conclude. Use thePerformance Task AssessmentList for Lab Report in PASC,p. 47. PP

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ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

309

Going FurtherGoing Further

Have students use Table 11.2to determine which aminoacids they “produced” in theBioLab. L1

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308 DNA AND GENES

RNA Transcription

A lthough DNA remains in the nucleus of a cell, it passes its infor-mation into the cytoplasm by way of another nucleic acid, messen-

ger RNA. The base sequence of this mRNA is complementary to thesequence in the strand of DNA, and is produced by base pairing duringtranscription. In this activity, you will demonstrate the process of tran-scription through the use of paper DNA and mRNA models.


ProblemHow does the order of bases in

DNA determine the order of bases inmRNA?

ObjectivesIn this BioLab, you will:■ Formulate a model to show how the

order of bases in DNA determinesthe order of bases in mRNA.

■ Infer why the structure of DNAenables it to be easily copied.

Materialsconstruction paper, 5 colorsscissorsclear tape

Safety PrecautionsBe careful when using scissors.

Always use goggles in the lab.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

Adenine

Deoxyribose

Parts for DNA Nucleotides Extra Parts for RNANucleotides

Phosphate

Ribose

Phosphate

Guanine

Uracil

Thymine

Cytosine


Time AllotmentOne class period

Process Skillssequence, observe and infer, rec-ognize cause and effect

Safety PrecautionsRemind students to use carewhen cutting with scissors and tocut away from their bodies.

■ Instead of having studentscopy models onto constructionpaper, you may wish to use themasters provided in theBioLab and MiniLab Work-sheets booklet. Copy theseonto white paper and have stu-dents color the models withpencils or crayons.

PREPARATIONPREPARATION

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PROCEDUREPROCEDURE

Teaching Strategies■ You may wish to give each student twoenvelopes to hold the nucleotide pieces.One can be used for the DNA nucleotidesand the other for the RNA nucleotides.■ To make larger, more varied models, thelab groups could pool their models.

Data and ObservationsStudents should construct a DNA moleculeand a complementary mRNA molecule.


Visually ImpairedCut out very large copies of the five differ-ent nucleotides (A, T, C, G, and U) so visu-ally impaired students can participate inthe BioLab.


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Chapter 11 AssessmentChapter 11 Assessment

SUMMARYSUMMARY

Section 11.1

Section 11.2

Section 11.3

Main Ideas■ DNA, the genetic material of organisms, is

composed of four kinds of nucleotides. A DNAmolecule consists of two strands of nucleotideswith sugars and phosphates on the outside andbases paired by hydrogen bonding on the inside.The paired strands form a twisted-zipper shapecalled a double helix.

■ Because adenine can pair only with thymine,and guanine can pair only with cytosine, DNAcan replicate itself with great accuracy. Thisprocess keeps the genetic information constantthrough cell division and during reproduction.

VocabularyDNA replication (p. 290)double helix (p. 289)nitrogen base (p. 288)

Main Ideas■ Genes are small sections of DNA. Most

sequences of three bases in the DNA of a genecode for a single amino acid in a protein.

■ The order of nucleotides in DNA determinesthe order of nucleotides in messenger RNA in aprocess called transcription.

■ Translation is a process through which theorder of bases in messenger RNA codes for theorder of amino acids in a protein.

Vocabularycodon (p. 297)messenger RNA (p. 295)ribosomal RNA (p. 296)transcription (p. 296)transfer RNA (p. 296)translation (p. 299)

Main Ideas■ A mutation is a change in the base sequence of

DNA. Mutations may affect only one gene, orthey may affect whole chromosomes.

■ Mutations in eggs or sperm affect future gener-ations by producing offspring with new charac-teristics. Mutations in body cells affect only theindividual and may result in cancer.

Vocabularychromosomal mutation

(p. 305)frameshift mutation

(p. 305)mutagen (p. 306)mutation (p. 302)point mutation (p. 304)

CHAPTER 11 ASSESSMENT 311

1. Which of the following processes requiresDNA replication?a. transcription c. mitosisb. translation d. protein synthesis

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 2. In which of the following processes does theDNA unzip?a. transcription and translationb. transcription and replicationc. replication and translationd. all of these

DNA: TheMolecule ofHeredity

From DNA toProtein

GeneticChanges

D

311

Main IdeasSummary statements can be used bystudents to review the major con-cepts of the chapter.

Using the VocabularyTo reinforce chapter vocabulary, usethe Content Mastery Booklet andthe activities in the Interactive Tutorfor Biology: The Dynamics of Life onthe Glencoe Science Web Site.www.glencoe.com/sec/science

1. c2. b

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS


All ChapterAssessment

questions and answers have beenvalidated for accuracy and suitabil-ity by The Princeton Review.


Chapter Assessment, pp. 61-66MindJogger VideoquizzesComputer Test BankBDOL Interactive CD-ROM, Chapter

11 quiz

Scanning probe microscopes can show thearrangement of atoms on the surface of a

molecule. They make it possible for scientists topick up molecules, and even atoms, and movethem around. They can also be used to observehow biological molecules interact. There aremany types of scanning probe microscopes. All ofthem use a very sharp probe that may be only asingle atom wide at its tip. The probe sits veryclose to the specimen, but does not actually touchit. As the probe moves across, or scans, the speci-men, it measures some property of the specimen.

The scanning tunneling microscope (STM)The STM uses a probe through which a tinyamount of electric current flows. As the probescans a molecule, it encounters ridges and valleysformed by the different kinds of atoms on themolecule’s surface. The probe moves up anddown as needed to keep the current constant. Themovements of the probe are recorded by a com-puter, which produces an image of the molecule.

The atomic force microscope (AFM) TheAFM can measure many different properties,including electricity, magnetism, and heat. As theprobe moves across the specimen, changes in theproperty being measured move the probe. Thesechanges are used to create the image.

What can they do? One of the primary advan-tages of scanning probe microscopy, besides itsatomic-level resolution, is the ability to observemolecules in air or liquid. This means that biolo-gists can “watch” molecules interact as theywould inside a cell. In 1998, for example, biolo-gists used the AFM to observe the behavior of anenzyme called RNA polymerase. This enzyme isinvolved in transcription. The AFM images showhow the polymerase molecule binds to a strand

of DNA and creates a strand of mRNA by gath-ering nucleotides from the surrounding liquid.

Applications for the FutureBiologists have used a combination of lasers

and an AFM to study the physical properties ofDNA molecules. Laser “tweezers” hold downone end of a coiled DNA helix and pull on theother end. The AFM measures the forces thathold the strand together and the forces thatcause it to coil and uncoil as it performs its func-tions in the cell.

310 DNA AND GENES

Scanning ProbeMicroscopes

Have you ever heard of someone dissecting a chromosome to get a closer look at DNA?Imagine an instrument small enough to allow you to grab hold of one of the nucleotides

in a strand of DNA, yet powerful enough to provide a detailed image.

TechnologyTechnologyBIOBIO

Thinking Critically What advantages do scan-ning probe microscopes have over other types ofmicroscopes?

To find out more about micro-scopes, visit the Glencoe Science

Web Site.www.glencoe.com/sec/science

INVESTIGATING THE TECHNOLOGYINVESTIGATING THE TECHNOLOGY

STM image of DNA

Magnification: 3 200 000�

310

PurposeStudents learn about the opera-tion and the capabilities of scan-ning probe microscopy.

BackgroundIf the current flowing through theprobe is increased slightly abovethe levels required to produce animage, a scanning probe micro-scope can pick up atoms and movethem around. Before the 1990s,molecules had to be removedfrom the cell for observation.

Teaching Strategies■ Explain to students that this isthe first type of microscopy capa-ble of producing images at thescale of the nanometer, the scaleat which molecular bondingoccurs. A nanometer is 10–9

meters, or 0.001 micrometers.These microscopes can also pro-duce images at somewhat largerscales, including 10–8, the scale ofthe DNA molecule, 10–7, thescale of the nucleus and otherorganelles, and 10–6, the scale ofintact cells.■ Point out that biology is notthe only field that has benefitedfrom the invention of scanningprobe microscopes. For example,physicists use them to look at thecrystal lattice structure of metalsand other materials. Chemists usethem to observe how moleculesbehave during chemical reac-tions. Materials scientists usethem to explore methods of fab-ricating ever-tinier computerchips.

Investigating the TechnologyScanning probe microscopes canshow the arrangement of atomson the surface of a molecule.Because specimens can be exam-ined in liquid or air, biologicalmolecules can be observed func-tioning as they would inside thecell.

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TechnologyTechnologyBIOBIO

Going FurtherGoing FurtherGoing Further

Intrapersonal Improvements to thismicroscope technology continue to

be made. Invite students to use the libraryor Internet to research recent images pro-duced by scanning probe microscopes. L2

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VIDEODISCThe Infinite VoyageUnseen Worlds

The Scanning Tunneling Microscope:Observing Atomic Particles (Ch. 10)

2 min.!8$.J"

VIDEOTAPEMindJogger Videoquizzes

Chapter 11: DNA and GenesHave students work in groups as they playthe videoquiz game to review key chapterconcepts.




CHAPTER 11 ASSESSMENT 313

22. Explain why codons can’t consist of two basesinstead of three for each amino acid.

23. A bricklayer has an assistant who bringsbricks to the bricklayer so she can build awall. What part of translation most closelyresembles the assistant’s job? What do thebricks represent?

24. Making Inferences Explain how the univer-sality of the genetic code is evidence that allorganisms alive today evolved from a com-mon ancestor in the past.

25. Analyzing Identify the type of chromosomalmutation illustrated in each diagram below.

26. Concept Mapping Complete the conceptmap by using the following vocabulary terms:transfer RNA, codons, messenger RNA,transcription, translation, ribosomal RNA.

THINKING CRITICALLYTHINKING CRITICALLY

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The following graph records the amount ofDNA in liver cells that have been grown ina culture so that all the cells are at the samephase in the cell cycle.

Interpreting Data Use the data in thegraph to answer the following questions.1. During the course of the experiment,

these cells went through cell division.What is this type of division called?a. transcription c. mitosisb. translation d. meiosis

2. During which hours were the cells carrying out cell division?a. 0-8 hours c. 12-14 hoursb. 8-10 hours d. 14-20 hours

3. Which phase of the cell cycle were thecells in during hours 2-6?a. interphase c. prophaseb. telophase d. anaphase

4. If you added radioactive thymine to theculture at 0 hour, what would happen tothe amount incorporated into the DNAbetween hours 20 and 28 relative to theamount at 0 hour?a. stay the same c. doubleb. divide in half d. triple

5. Predicting Predict what will be theDNA content of the cells, in picograms,at 33 hours.

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web Site.www.glencoe.com/sec/science

CD-ROM

5. 6.

3.

which is madeup of

2.

4.1.

combines amino acids in process of

Protein synthesis

firstrequires

to makethat occurs with

the help of

and

for use in

a

b

c

K L M N O P R Q S

K L M N O P Q X Y R

F G H I J K M N

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A (p

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ram

s/cel

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Time (hours)2

0.1

0

0.2

0.3

0.4

0.5

0.6

6 10 14 18 22 26

Change in DNA content per cell

313

22. A sequence of two bases offour different kinds will pro-duce 16 different combinations.The nucleotides must code forat least 20 amino acids.

23. The bricklayer’s assistant is anal-ogous to transfer RNA. Thebricks represent amino acids.

24. The genetic code of all organ-isms is based on the same fournucleotides and the samesequences, suggesting a link toa common ancestor.

25. (a) inversion; (b) deletion; (c)insertion

26. 1. Transcription; 2. MessengerRNA; 3. Codons; 4. Translation;5. and 6. Transfer RNA, Ribo-somal RNA

THINKING CRITICALLYTHINKING CRITICALLY


1. c2. c3. a4. c5. The DNA content will

drop to 0.3 picograms/cell.


3. Which DNA strand can base pair to the fol-lowing DNA strand?

a. T-A-C-G-A-T c. U-A-C-G-A-Ub. A-T-G-C-T-A d. A-U-G-C-U-A

4. Which of the following nucleotide chainscould be part of a molecule of RNA?a. A-T-G-C-C-A c. G-C-C-T-T-Gb. A-A-T-A-A-A d. A-U-G-C-C-A

5. Which of the following mRNA codonswould cause synthesis of a protein to termi-nate? Refer to Table 11.2.a. G-G-G c. U-A-Gb. U-A-C d. A-A-G

6. A DNA sequence of A-C-C would create anmRNA codon for which amino acid? Refer toTable 11.2.a. tryptophan c. leucineb. serine d. phenylalanine

7. The genetic code for an oak tree is ________.a. more similar to an ash tree than to a squirrelb. more similar to a chipmunk than to

a maple treec. more similar to a mosquito than to

an elm treed. exactly the same as for an octopus

8. Which of the following base pairs would notbe found in a cell?a. adenine—thymine c. thymine—uracilb. cytosine—guanine d. adenine—uracil

9. A protein is assembled amino acid-by-aminoacid during the process of ________.a. replication c. transcriptionb. translation d. mutation

10. A deer is born normal, but UV rays cause amutation in its retina. Which of the follow-ing statement is least likely to be true?a. The mutation may be passed on to the

offspring of the deer.b. The mutation may cause retinal cancer.c. The mutation may interfere with the

function of the retinal cell.d. The mutation may interfere with the

structure of the retinal cell.11. In the process of ________, enzymes make an

RNA copy of a DNA strand.12. The RNA copy that carries information from

DNA in the nucleus into the cytoplasm is________ RNA.

13. DNA is copied before a cell divides in theprocess called ________.

14. Molecules of ________ bring amino acids tothe ________ for assembly into proteins.

15. The shape of a molecule of DNA is called a________.

16. RNA has a ribose sugar, whereas DNA has a________ sugar.

17. Nucleotides form base pairs through a weakbond called a ________ bond.

18. A female lab rat is exposed to X rays. Itsfuture offspring will be affected only if amutation occurs in the rat’s ________ cells.

19. Chemical Q causes the following change inthe sequences of nucleotides. This change isan example of a ________. Chemical Q is a________.

20. DNA ________ is necessary before a celldivides so each cell has a complete copy ofthe chromosomes.

21. Explain why a mutation in a lung cell wouldnot be passed on to offspring.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

312 CHAPTER 11 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Use as Much Time as You Can You will not get extra points for finishing early.Work slowly and carefully on any test and makesure you don’t make careless errors because youare hurrying to finish.

AA TT G C

TAA T G AA T A AA A

312

3. a4. d5. c6. a7. d (Remember the genetic code

is the same for all living things.)8. c9. b

10. a11. transcription12. messenger13. replication14. transfer RNA, ribosomes or

mRNA15. double helix16. deoxyribose17. hydrogen18. reproductive19. point mutation, mutagen20. replication

21. The lung cell mutation does notaffect the reproductive cells.Thus, this mutation would notbe passed on to offspring.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS



chapter 11: dna and genes · life’s genetic blueprint,” by robert f. weaver, december 1984....

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