Course: Biology Agricultural Science & Technology

Unit: DNA

State Standard: Students will understand that genetic information coded in DNA is passed from parents to offspring by sexual and asexual reproduction. The basic structure of DNA is the same in all living things. Changes in DNA may alter genetic expression.

State Objectives: Explain how the structure and replication of DNA are essential to heredity and protein synthesis.

a. Use a model to describe the structure of DNA.b. Explain the importance of DNA replication in cell reproduction.c. Summarize how genetic information encoded in DNA provides instructions for assembling protein

molecules.e. Relate the historical events that lead to our present understanding of DNA to the cumulative nature

of science knowledge and technology.

Unit Objectives:

A. Describe the structure of a DNA molecule and the history of its discovery.

B. Explain the process of DNA replication and understand its relevance to cell division.

C. Describe the structure of RNA and identify the steps associated with protein synthesis.

Materials Needed (Equipment):

Pre-cut paper nucleotide bases for DNA activity – Print or copy enough so that each

person in the class has one nucleotide base (Click here for nucleotide activity cards) Red and black licorice sticks, colored marshmallows or gummy bears, toothpicks and

string. (Click here for the Candy DNA Lab Activity) The following supplies are for the DNA Extraction Lab (Optional)

Split green peasTable SaltCold waterBlenderStrainerDetergent (Dawn)Meat tenderizerRubbing alcoholTest tubeWooden skewersMixing bowlBeaker

Facilities:

Classroom

PowerPoint

Projector

Interest Approach:

A: Take a stack of books and have students imagine how much information is held in

the stack of books. Explain how small a molecule of DNA is. (You need a microscope

to see a cell). Explain that a molecule of DNA has much more information on it than in

the stack of books on the table and that DNA is what makes living organisms what they

are.

B: Demonstrate or have groups do a DNA Extraction Lab

o Click here to follow the link to the DNA Extraction Lab

Objective A: Identify the structure of a DNA molecule.

Curriculum (Content)(What to teach)

Instruction (Methodology)(How to teach)

A1

A2

Deoxyribonucleic Acid

• DNA is the molecule responsible

for controlling the activities of the cell

• It is the hereditary molecule

• DNA directs the production of

protein

A3

Structure of DNA

• In 1953, Watson and Crick

proposed that DNA is made of two chains

of nucleotides held together by nitrogenous

bases.

• Watson and Crick also proposed

that DNA is shaped like a long zipper that

is twisted into a coil like a spring.

A4

Structure of DNA

• Because DNA is composed of two

strands twisted together, its shape is called

double helix.

• A double helix resembles a twisted

Have a class discussion on what students know about DNA and list on board.

Have a class discussion about what DNA is made up of.Have a student draw a diagram of DNA on the board.

A1. PPT Slide 1A2. PPT Slide 2

A3. PPT Slide A3

A4. PPT Slide A4

A5. PPT Slide 5

What is DNA?

What is DNA made of and what does it look like?

Activity: How to Make a DNA Model Using CandyHere's How:

1. Gather together red and black licorice sticks, colored marshmallows or gummy bears, toothpicks and string.

2. Assign names to the colored marshmallows or gummie bears to represent nucleotide bases. There should be four different colors each representing either adenine, cytosine, guanine or thymine.

3. Assign names to the colored licorice pieces with one color representing the pentose sugar molecule and the other representing the phosphate molecule.

4. Cut the licorice into 1 inch pieces. 5. String half of the licorice pieces together lengthwise alternating between the black

and red pieces. 6. Repeat the procedure for the remaining licorice pieces to create a total of two stands

of equal length.7. Connect two different colored marshmallows or gummy bears together using the

toothpicks.8. Connect the toothpicks with the candy to either the red licorice segments only or the

black licorice segments only, so that the candy pieces are between the two strands.9. Holding the ends of the licorice sticks, twist the structure slightly.

Tips:

1. When connecting the base pairs be sure to connect the ones that pair naturally in DNA. For example, adenine pairs with thymine and cytosine pairs with guanine.

2. When connecting the candy base pairs to the licorice, the base pairs should be connected to the licorice pieces that represent the pentose sugar molecules.

A14 Go Get It Moment!• When you hear “Move it!” you will have 30 seconds to come get one piece of paper with an A, G, T, or C on it.• Then find someone else in the room whose letter correctly matches with your nucleotide letter and stand by that person.• What are the questions?• “Move it!”

A28Go Get It Moment!• When you hear “Double Helix”, you will have 1 minute to make a classroom

A14. PPT Slide 14 Place your pre-cut nitrogen base papers somewhere in the room where students can access them easily and follow the prompt on the PPT slide 14. When you are ready for the students to get started, click onto the next slide and there is an automatic 30 second timer.

A28. PPT Slide 28Follow the prompt on the PPT slide 28 and when you are ready for the students to get started, click onto the next slide and there is an automatic timer for 1 minute. Have the

DNA strand by standing next to another pair of nucleotides• What questions are there?

• “Double Helix”

students keep their nucleotide paper letter and remember their partner and their place in the DNA strand for a future activity.

Objective B: Explain the process of DNA replication and understand its

relevance to cell division.

How can people benefit from understanding the structure of a DNA molecule? (Understanding the structure of a DNA molecule can help us understand genetic disorders, solve

crimes, paternity testing, genetic engineering, cloning, etc.)

B45DNA Replication

• In order for cells to divide, DNA must be able to make exact copies of itself– This process is known as DNA Replication

B46DNA Replication

• DNA Replication occurs before mitosis and meiosis

• Replication results in two identical DNA daughter strands from one mother strand

B47Process of DNA Replication

• The DNA strand is unzipped at the hydrogen bonds by an enzyme named helicase.

• Nucleotides in the nucleus then find their corresponding nucleotides on each of the two open DNA strands and produce two new DNA double helixes.

B48Link to DNA Replication Animation

• Click here to see how DNA Replication works

Students should have already learned about mitosis and meiosis. Answers should refer back to Interphase in cell division where DNA replication occurs in order for the cell to divide with the appropriate amount of DNA.

B45. PPT Slide 45

B46. PPT Slide 46

B47. PPT Slide 47

B48. PPT Slide 48Show Internet animation to illustrate the process of DNA replication

Why is DNA replication necessary in living organisms?

Objective C: Identify the steps associated with protein synthesis.

Interest Approach for Objective C:

C49Protein Synthesis

• The main job for DNA is to direct the production of protein

• Protein makes tissues and organs and carries out the organism’s metabolism

• Proteins are polymers (chains) of amino acids

C50Protein Synthesis

• The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein

C51RNA• RNA is a nucleic acid composed of

Discuss or write on the board foods high in protein. (Eggs, meat, beans, etc.)

Discuss or write on the board reasons why protein is an important nutrient. (Good for muscles, hair, nails, etc.)

Discuss where protein comes from.(Likely, students have never considered this question before now. Some may say that they get protein from the food they eat. Follow this with the question, “where did the plant or animal get the protein from?”)

C49. PPT Slide 49

C50. PPT Slide 50

C51. PPT Slide 51On the board, make two columns.Write DNA on top of one column and RNA at the top of the other column. List the following characteristics of DNA and then write the characteristics of RNA and note comparisons

What have you eaten today that contained a lot of protein?

Why should you eat protein?

Where does protein come from?

nucleotides that is crucial in making protein• There are three differences between DNA and RNA– RNA is a single strand– The sugar in RNA is called Ribose instead of DNA’s Deoxyribose– Like DNA, RNA has 4 nitrogenous bases, but instead of Thymine, Uracil is the 4th base

C52RNA as a Single Strand• You recall that DNA looks like a twisted ladder and is referred to as a double helix• RNA looks like half a ladder– There is only one side to RNA

C53RNA Contains Ribose

• Remember how DNA got its name?– It is a nucleic acid with deoxyribose as the sugar on the backbone– Hence the name Deoxyribonucleic acid

• Ribonucleic acid (RNA) has the sugar ribose on it’s backbone

C54RNA Has Uracil• Remember the base pairs in DNA?– Adenine pairs with Thymine– Guanine pairs with Cytosine

among the two.

(Sample of what this may look like)DNA RNA

Double helix

Sugar is called Deoxyribose

Bases are T, A, C, and G

Single stranded molecule

Sugar is Ribose

Uracil replaces thymine

C52. PPT Slide 52

C53. PPT Slide 53

C54. PPT Slide 54

C55RNA Has Uracil• In RNA– Adenine pairs with URACIL– Guanine pairs with Cytosine

C56Making Protein• Protein production starts with DNA• DNA passes instruction to RNA• RNA carries out the work of linking together chains of amino acids

C57Three Types of RNA

• There are three types of RNA involved in Protein Synthesis– Messenger RNA (mRNA)– Ribosomal RNA (rRNA)– Transfer RNA (tRNA)

C58Messenger RNA• Messenger RNA (mRNA), brings instructions from DNA in the nucleus to the cell’s factory floor, the cytoplasm– On the factory floor, mRNA moves to the assembly line, a ribosome– Remember that a ribosome is either a free-floating small dot in the cell or is attached to the endoplasmic reticulum making it “rough” ER

C59Ribosomal RNA

• The ribosome, made of Ribosomal RNA (rRNA) binds to the mRNA and uses the instructions to assemble the amino acids in the

C55. PPT Slide 55

C56. PPT Slide 56

C57. PPT Slide 57You may give the types of RNA names for the “story” given below at slide 61.DNA = DeenamRNA = MyrnatRNA = Trina

C58. PPT Slide 58

C59. PPT Slide 59

C60. PPT Slide 60

correct order

C60Transfer RNA

• Transfer RNA (tRNA) is the supplier

• Transfer RNA delivers the amino acids to the ribosome to be assembled into a protein

C61Transcription• The production of messenger RNA (mRNA) is known as Transcription• DNA acts as a template for the RNA molecule• To View a Link to Transcription Animation Click Here.

C62Transcription• The main difference between DNA Replication and transcription is that transcription results in one single strand of RNA rather than an exact duplicate of a double stranded DNA molecule• Much of the information on the mRNA strand codes for specific amino acids to make protein

C63The Genetic Code• A code is necessary to turn the language of RNA into the language of amino acids and proteins• The four nitrogenous bases make up the

C61. PPT Slide 61“The Protein Synthesis Story”Myrna, the messenger girl(mRNA) is at work one day and her boss Deena (DNA) calls her into her office (the nucleus). Deena tells Myrna that she is going to give her a specific recipe for a new protein needed elsewhere in the city (the organism). She gives her the “secret” recipe code and Myrna writes it down. (This is known as transcription).(This occurs when the DNA molecule is unzipped like in replication, except the free floating nucleotides that fill in on the DNA molecule are RNA nucleotides and when it releases itself from the DNA the resulting product is a single stranded mRNA molecule)(Story continued on slide 69)

C62. PPT Slide 62

C63. PPT Slide 63

code– The code letters are A, G, T, and C• A set of three letters makes a “word” called a Codon– There are 64 possible codons

C64Codon

C65Amino Acids• There are 20 different amino acids that make up proteins

C66The Genetic Code

C67The Genetic Code• As you could see on the chart of amino acids, there are more than one codon that code for certain amino acids – This results in fewer errors in protein synthesis

C68The Genetic Code• All organisms use the same genetic code• This provides evidence that all life on earth may have evolved from the same origin

C64. PPT Slide 64

C65. PPT Slide 65

C66. PPT Slide 66Take time to briefly discuss the 20 different amino acids and the codons that code for them at the side of each one.

C67. PPT Slide 67

C68. PPT Slide 68

C69. PPT Slide 69“Protein story continued”Remember that Myrna got the secret recipe for a specific type of protein? Now Myrna leaves the office (Nucleus) and goes into the cytoplasm to find a ribosome (where the protein is made).

C69Ribosomes• The newly produced strand of mRNA travels from the nucleus to the cytoplasm where it attaches to a ribosome• The ribosome is the actual site for protein synthesis

C70Translation: From mRNA to Protein• The process of “reading” the three letter “words” , or codons, is known as translation• Translation takes place at the ribosomes in the cytoplasm– The amino acids are free-floating in the cytoplasm and congregate at the ribosome during protein synthesis

C71The Process of Protein Synthesis• The first codon is usually A-U-G, methionine, which starts the production of a new protein• Following the start codon, the remaining codons call for amino acids in the order in which they appear on the mRNA strand

C72Transfer RNA (tRNA)• At the ribosome, Transfer RNA (tRNA) identifies the code through translation and finds the appropriate amino acid matching the codons– Each tRNA molecule only attaches to one specific amino acid– The Anticodon on the bottom of the tRNA molecule corresponds with the codons on the mRNA strand

C70. PPT Slide 70“Protein story continued”Myrna is now at the ribosome where the protein will be created. She finds Trina (tRNA), who is the “cook” who puts the ingredients together, and gives the secret protein recipe code from Deena, the boss. Trina then translates the code using a special tool called anticodons. (This process is called translation)

C71. PPT Slide 71

C72. PPT Slide 72

“Protein story continued”Trina, who has the recipe now and has translated the code using anticodons, starts taking ingredients (amino acids) off of the shelf and chaining them together at the ribosome to produce the final product, the protein molecule.

C73. PPT Slide 73This link will show an animation of the process of protein synthesis and should give students a good review of the process.

Sample TestClick here to link to a sample DNA test

C73Protein Synthesis Animation– Click Here to Link to An Animation

AssessmentAssess students understanding of DNA