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Chapter 21

DNA Biology and TechnologyThis is Cindy Cutshall.

What condition did she have?

SCID!!!?

Severe Combined Immunodeficiency.

It was treated with Gene Therapy!

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Outline (Modified)

• DNA Structure and Function• DNA Replication• RNA Structure and Function

– Types of RNA• Gene Expression

– Structure and Function of Proteins– Transcription– Translation

• Genomics• DNA Technology

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DNA and RNA Structure and Function

• DNA is the genetic material (genome)found principally in chromosomes.

• Deoxyribonucleic acid• It is the nucleic acid of all life.

– In between cell divisions, chromosomes exist in long fine threads of chromatin.

When a cell is about to divide, chromosomes coil and condense, becoming distinctly visible.

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DNA Location and Structure

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DNA Structure and Replication

• DNA is a sequential series of joined nucleotides which consist of:– Sugar (deoxyribose), phosphate, and base.

Adenine (A).Thymine (T).Cytosine (C).Guanine (G).

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DNA Structure and Replication

• DNA is a double helix (Watson & Crick Model) with a sugar-phosphate backbone (“sides of the ladder”) and bases projecting between the backbones (“steps of the ladder”).– Exhibits

complementary base pairing.

A-T.G-C.

HISTORICAL FOCUS

Overlooked Genius: Rosalind Franklin

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DNA Replication• Occurs during chromosome duplication.• Replication Steps.

– DNA serves as it’s own template (pattern).– Hydrogen bonds between strands break

and the molecule unzips (helicase).– New nucleotides fit beside parental strand.– DNA polymerase joins new nucleotides.– Two complete molecules present, each with

one old strand and one new strand.Thus, termed “Semi-conservative

replication”.

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DNA Replication

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Video

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Structure and Function of RNA

• Ribonucleic acid.• RNA is made up of nucleotides containing

the sugar ribose and the base uracil in place of thymine.– Single stranded.

RNA is a helper to DNA allowing protein synthesis.

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Types of RNA

• Ribosomal RNA (rRNA).– Joins with proteins made in the cytoplasm

to form the subunits of ribosomes.• Messenger RNA (mRNA).

– Carries genetic information from DNA to the ribosomes in the cytoplasm where protein synthesis occurs.

• Transfer RNA (tRNA).– Transfers (“shuttles”) amino acids to the

ribosomes where amino acids are joined.

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Types of RNA

• Small RNAs – are divided into several classes:– Small nuclear RNAs (snRNAs) are

involved in editing the mRNA.– Small nucleolar RNAs (snoRNAs) modify

rRNAs within the nucleolus of the cell.– MicroRNAs (miRNAs) attach to mRNAs in

the cytoplasm preventing unnecessary translation.

– Small interfering RNAs (siRNAs) bind to mRNAs to prepare mRNA for degradation.

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Gene Expression• Genes are expressed when a protein product

occurs in the cell.• Structure and Function of Proteins • Structural functions, enzymes.

– Proteins are composed of amino acids (#20). Proteins differ because the number and

order of their amino acids differ.

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Nucleic Acids• Nucleic acids are huge macromolecules

composed of nucleotides. – A nucleotide is constructed of a phosphate,

a pentose sugar, and a nitrogenous base.– Deoxyribonucleic acid (DNA).

Double-stranded helix.The molecule of inheritance.

– Ribonucleic acid (RNA).Single stranded.A helper to DNA.

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The Genetic Code• Genetic code is essentially universal.• A gene is a sequence of DNA (along a chromosome)

that codes for a protein.– Contains a “triplet code”.

Every three bases represents one amino acid. A language using a 4-letter alphabet, made up

of 3-letter words, and with 64 possible words.• Transcription.

– DNA serves as template (“pattern”) for mRNA.– Strand of mRNA forms that is complementary to a

portion of DNA.– The triplet of mRNA is termed a codon.

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RNA Transcription

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Video

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Processing of mRNA

• Most human genes are interrupted by introns.– These “intragene” segments interrupt

gene segments, exons (expressed).During processing in the nucleus,

introns are removed and exons are joined to form an mRNA molecule.

Is like the “editing” of a sentence.Primary mRNA becomes mature MRNA

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Function of Introns

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Translation• Translation is the synthesis of a polypeptide

under the direction of an mRNA molecule (the “message”).– Transfer RNA molecules (“shuttle”) bring

amino acids to the ribosomes (“translators”).Anticodon (on tRNA) is a triplet

complementary to an mRNA codon.• Polypeptide synthesis requires three steps.

– Initiation.– Elongation.– Termination.

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Anticodon-Codon Base Pairing

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Check out this website of animations:

http://vcell.ndsu.nodak.edu/animations/

(which is also available through the course website).

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Review of Gene Expression• DNA triplet codes for a specific amino acid.• During transcription, a segment of DNA serves

as a template for mRNA.• Messenger RNA has introns removed (“edited”).• Messenger RNA carries a sequence of codons

to the ribosomes.• Transfer RNA molecules have anticodons

complementary to mRNA codons.• Linear sequence of mRNA codons determines

order amino acids are incorporated into a protein.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

DNA

C T C A

C

TC C C G T T G

G AA G UG G G C A A

gly ser ala asn

codon codon codon codon

Transcription

Translation

DNA strand

mRNA

polypeptide

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*

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Video

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rRNA Ribosome Site of protein synthesis

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Regulation of Gene Expression

• Gene Regulation Mechanisms.– Pretranscriptional control (in nucleus).– Transcriptional control (in nucleus).– Posttranscriptional control (in nucleus).– Translational control

(in cytoplasm at ribosome).– Posttranslational control.

• Also, involves activated chromatin and transcription factors.

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• Activated chromatin.– For genes to function in cells, the chromosome must first decondense (“unwind”) in the area to transcribed.

• Transcription factors.– DNA-binding proteins that regulate gene activity during cell specialization.

36Lampbrush Chromosomes

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Genomics

• is the study of genomes – our genes, and the genes of other organisms.

• Genome is all the genetic information of an individual or species.

• The Human Genome Project (HGP)• The project (a 13 year effort) had two goals:

– (1) to know the sequence of genes on all the human chromosomes.

– (2) to know the sequence of bases on all the human chromosomes.

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The Human Genome

– The base sequence map.Shows sequences of all base pairs.3 billion base pairs.

Completed for humans.– The genetic map.

Shows locations of genes along each chromosome.

The estimated ~100,000 was ~33,000It could be that one day gene therapy

can replace defective genes.

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The Human Genome

• ~ finished for humans . . . . . . .• Only 20 – 25,000 genes (20,500) !!!!!• What are the issues of concern?

– $!– Patents!– An example is the genetic map of

chromosome 17.

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Functional and Comparative Genomics• Functional genomics – how genes function.• The genomes of a number of other

organisms are also in the final-draft stages.• There are many similarities between the

sequence of our bases and those of other organisms – we share common genes!

• There are also many differences.• For example, in comparing our genome with

chromosome 22 in chimpanzees, many genes differed in sequence, including a gene for proper speech development, several for hearing and several for smell.

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The Human Genome– 3 mammal species that have been deciphered:

humans, mice, and the rat (Nature, March, 04).– After 4 years, 220 researchers completed draft of

90% on the laboratory (Norway) rat DNA sequence.– Humans: 2.9 billion base pairs.– Rat: 2.75 billion base pairs.– Mouse: 2.6 billion base pairs. – Rats first appeared in lab research in 1828.– Rodents consume 1/5 the world’s food supply.– Other genomes being analyzed include. . . . – chimpanzee, rhesus monkey, cow, chicken, dog,

frog, many others.

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Proteomics and Bioinformatics

• Proteomics is the study of the structure, function, and interaction of cellular proteins.

• For example, the translation of most of the human genes will result in a collection of proteins called the human proteome.

• An important part is computer modeling of the 3-dimensional shape of these proteins.

• Understanding protein function is also essential to the discovery of better, more efficient drugs with fewer side effects.

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Proteomics and Bioinformatics

• Bioinformatics is the application of computer technologies to the study of the genome.

• Using computer analysis of the raw data produced by genomics and proteomics, scientists are hopeful of finding cause-and-effect relationships between various genetic profiles and genetic disorders caused by multifactor (polygenic) genes.

• We may also be able to determine the function of 82 gene “deserts” in the human genome.

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A Peron’s Genome Can Be Modified• Gene therapy is the insertion of genetic material

into human cells to treat a disorder.– “Ex Vivo” Gene Therapy.

“outside the body”. Bone marrow stem cells are removed from the

body, an RNA retrovirus is used to insert a normal gene into them, and the stem cells are returned to the body.

Used to treat patients with…… SCID (severe

combined immunodeficiency) hypercholesterolemia ? hyper / cholesterol / emia

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A Person’s Genome Can Be Modified– “In Vivo” Gene Therapy.

“inside the body”. Genes injected alone, or with a virus, directly

into the organ, or the body. Is currently used to treat cystic fibrosis (CF) by

the patient inhaling an aerosol containing the correct gene to replace the defective one in lung tissue via adenovirus or liposomes.

Helps form new blood vessels to improve coronary circulation (VEGF).

Used in cancer therapy to make healthy cells more tolerant to chemotherapy and cancer cells more sensitive.

May one day cure hemophilia, diabetes, Parkinson’s disease, and AIDS.

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DNA Technology

• Genetic engineering is the use of technology to alter the genomes of organisms.

• It allows the insertion of a foreign gene into new cells, which are then able to produce a different product.– Biotechnology includes genetic

engineering and other techniques to make use of natural biological systems to achieve an end desired by humans.

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Genes Can Be Isolated and Cloned• When many copies of the same gene are obtained,

the gene is said to be cloned - is accomplished by:• Recombinant DNA (rDNA) Technology.

– DNA from at least two different DNA sources. Vector used to introduce foreign DNA into a host

cell. Plasmids (from bacteria), viral DNA,

retroviruses.• Enzymes to “cut and seal”.

– Restriction enzymes cleave DNA (“molecular scissors”) to produce “sticky ends”.

– DNA ligase seals DNA into an opening created by the restriction enzyme (“molecular glue”).

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• Producing the foreign protein.

• Once cell has taken up the vector and the gene functions normally, the cell has been transformed . . . .

• that is, it can produce a protein it never produced before.

• The cloned gene or a protein product may be recovered.

• Check out the ”Recombinant DNA” notes on the web site.

• The classic successful example of this process -

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Specific DNA Sequences Can Be Cloned

• There are additional applications of this technology.

• Polymerase Chain Reaction (PCR) can create millions of copies of a single gene or a DNA segment very quickly.

• Uses “primers” (on either side of the target DNA) to get the chain reaction started and DNA polymerase.

• Used as a confirming test for HIV infection.

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Analyzing DNA Segments

• DNA can be subjected to DNA fingerprinting using restriction enzymes to cleave the DNA sample.

• This produces fragments that form a pattern when separated according to their length using a process called gel electrophoresis.

• Matching patterns can identify a criminal (ie.rape case) or the parent of a child (maternity or paternity), remains of a body.

• See – Figure 21.19 (p.506 in text).

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• Patterns can also help with medical diagnoses and tracing the evolution of humans and other species.

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Biotechnology Products• Transgenic organisms have a foreign gene

inserted into them.• Transgenic Bacteria.

– Insulin.– Human Growth Hormone.– Hepatitis B vaccine.– Promote plant health.– Degrade wastes.– Produce chemicals.– Help mine metals.

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Biotechnology Products

• Transgenic Plants.– Hormones, clotting factors, antibodies.– Salt-tolerant, drought-tolerant, cold-

tolerant.– Disease protected.– Herbicide resistance.– Pest resistance.

Higher yields.– See Health Focus: Are Genetically

Engineered Foods Safe? (p. 509).

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Biotechnology Products

• Transgenic Animals.– The use of transgenic farm animals to

produce pharmaceuticals in the milk of females is currently being pursued.

– Referred to as “gene pharming”.– To produce drugs for treating CF, cancer,

blood diseases, etc.Cloning transgenic animals.

Dolly (1997).

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Animal Organs as Biotechnology Products• Xenotransplantation?• Transplantation of an organ or tissue from one

species (ie. animal) to a different species (ie. humans).

• Scientists have begun genetically engineering pigs to serve as organ donors for humans who need transplants.

• They are gradually making the organs less antigenic to humans.

• Main concern: pig’s organs might carry animal viruses into humans. (HIV believed to have come from monkeys into humans!)

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BIOETHICAL FOCUS

DNA Fingerprinting and the Criminal Justice

System

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Outline

• DNA Structure and Function• DNA Replication• RNA Structure and Function

– Types of RNA• Gene Expression

– Structure and Function of Proteins– Transcription– Translation

• Genomics• DNA Technology

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