Go to Section: Interest Grabber Order! Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message. Section On a sheet of paper, write the word cats. List the letters or units that make up the word cats. 2. Try rearranging the units to form other words. Remember that each new word can have only three units. Write each word on your paper, and then add a definition for each word. 3. Did any of the codes you formed have the same meaning? 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message?

Go to Section: Section Outline 12–1DNA A.Griffith and Transformation 1.Griffith’s Experiments 2.Transformation B.Avery and DNA C.The Hershey-Chase Experiment 1.Bacteriophages 2.Radioactive Markers D.The Components and Structure of DNA 1.Chargaff’s Rules 2.X-Ray Evidence 3.The Double Helix Section 12-1

Go to Section: Fred Griffith’s Transformation

Go to Section: Avery’s Experiment

Go to Section: Frederick Griffith’s Experiment Mice infected with live coated bacteria (S strain) died of pneumonia Mice infected with live uncoated bacteria (R strain) survived Mice infected with heat killed coated bacteria (S strain) survived

Go to Section: Frederick Griffith’s Experiment Mice infected with both live uncoated bacteria and heat killed coated bacteria died ‡

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Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Figure 12–4 Hershey-Chase Experiment Section 12-1

Go to Section: Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Section 12-1 Figure 12–4 Hershey-Chase Experiment

Go to Section: Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Section 12-1 Figure 12–4 Hershey-Chase Experiment

Go to Section: Structure of DNA DNA is made of chains of nucleotides a Nucleotide is made of three subunits –phosphorus group –5 carbon sugar group –nitrogenous base

Go to Section: Structure of DNA DNA has four types of nucleotides, each with a different nitrogenous base: –A=Adenine –G=Guanine –C=Cytosine –T=Thymine

Go to Section: PurinesPyrimidines AdenineGuanine CytosineThymine Phosphate group Deoxyribose Figure 12–5 DNA Nucleotides Section 12-1

Go to Section: Percentage of Bases in Four Organisms Section 12-1 Source of DNAATGC Streptococcus Yeast Herring Human Streptococcus Yeast Herring Human

Go to Section: Chargaff’s Rule Chargaff found that the amount of adenine in an organism is always equal to the amount of thymine (A=T) Also, he found that the amount of cytosine always equals the amount of guanine (C=G). This suggested that DNA had some sort of regular structure where the pairing of these bases are involved

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Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. What percent of the nucleotides in this sample will be thymine? A.12 B.24 C.31 D.38 E.It cannot be determined from the information provided.

Go to Section: In an analysis of the nucleotide composition of DNA, which of the following is true? A.A = C B.A = G and C = T C.A + C = G + T D.A + T = G + C E.Both B and C are true

Go to Section: In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules? –A = G –A + G = C + T –A + T = G + T –A = C –G = T

Go to Section: Franklin Franklin did X-ray diffraction studies on DNA Photographs suggested that the DNA molecule resembled a tightly coiled spring - a helix ‡30167

Go to Section: Figure 16.6 Rosalind Franklin and her X-ray diffraction photo of DNA (a) Rosalind Franklin Franklin’s X-ray diffraction Photograph of DNA (b)

Go to Section: X-Ray diffraction of DNA indicated that DNA was 2nm thick and has a helical structure, one full turn every 3.4nm, 10 bases per turn

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WATSON AND CRICK Using Chargaff’s rule and the information from Franklin about the shape of DNA Watson & Crick determined the structure of the DNA molecule and how it makes a copy of itself.

Go to Section: WATSON AND CRICK DNA is made of two strands of nucleotides chains that wind around each other This DNA structure is called a: –double helix

Go to Section: Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Figure 12–7 Structure of DNA Section 12-1

Go to Section: Interest Grabber A Perfect Copy When a cell divides, each daughter cell receives a complete set of chromosomes. This means that each new cell has a complete set of the DNA code. Before a cell can divide, the DNA must be copied so that there are two sets ready to be distributed to the new cells. Section 12-2

Go to Section: Interest Grabber continued Section On a sheet of paper, draw a curving or zig-zagging line that divides the paper into two halves. Vary the bends in the line as you draw it. Without tracing, copy the line on a second sheet of paper. 2.Hold the papers side by side, and compare the lines. Do they look the same? 3.Now, stack the papers, one on top of the other, and hold the papers up to the light. Are the lines the same? 4.How could you use the original paper to draw exact copies of the line without tracing it? 5.Why is it important that the copies of DNA that are given to new daughter cells be exact copies of the original?

Go to Section: 12–2Chromosomes and DNA Replication A.DNA and Chromosomes 1.DNA Length 2.Chromosome Structure B.DNA Replication 1.Duplicating DNA 2.How Replication Occurs Section 12-2 Section Outline

Go to Section: Chromosome E. coli bacterium Bases on the chromosome Prokaryotic Chromosome Structure Section 12-2

Go to Section: Figure Chromosome Structure of Eukaryotes Chromosome Supercoils Coils Nucleosome Histones DNA double helix Section 12-2

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WATSON AND CRICK The double helix looks like a twisted ladder The sides of the ladder are made of alternating sugar and phosphate groups –the sugar and phosphate groups form the backbone of the DNA molecule The steps or rungs of the ladder are made of nitrogenous base pairs ‡

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WATSON AND CRICK Adenine and Guanine are double ring structures called purines Cytosine and Thymine are single ring structures called pyrimidines In DNA, A always pairs with T and G always pairs with C

Go to Section: A Purine always pairs with a Pyrimidine A with T G with C. X-Ray diffraction of DNA indicated that DNA was 2nm thick

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Antiparallel

Go to Section: DNA REPLICATION DNA must make a copy of itself during Interphase Watson and Crick postulated that the DNA molecule unzipped itself between the bases (because of the weak bonds) –Once opened, the exposed bases could serve as a template, allowing floating nucleotides to bond with them and follow their pattern in forming new DNA strands

Go to Section: Link to DNA Replication DEMO

Go to Section: Old DNA strands act as a template for the new DNA strands New DNA is half old and half new

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1. What do the yellow strands of DNA represent? new DNA strands Semi-conservative replication

Go to Section: Figure 12–11 DNA Replication occurs at replication bubbles Section 12-2 Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand

Go to Section: Telomeres include incomplete ends to the DNA

Go to Section: telomere

Go to Section: Telomeres protect the ends of the DNA, but become shorter during each replication

Section 1 Answers Interest Grabber Answers 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats. The units that make up cats are c, a, t, and s. 2. Try rearranging the units to form other words. Remember that each new word can have only three units. Write each word on your paper, and then add a definition for each word. Student codes may include: Act; Sat; Cat 3. Did any of the codes you formed have the same meaning? No 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message? Changing the order of the nucleotides changes the meaning of the codon.

Section 2 Answers Interest Grabber Answers 1.On a sheet of paper, draw a curving or zig-zagging line that divides the paper into two halves. Vary the bends in the line as you draw it. Without tracing, copy the line on a second sheet of paper. 2.Hold the papers side by side, and compare the lines. Do they look the same? Lines will likely look similar. 3.Now, stack the papers, one on top of the other, and hold the papers up to the light. Are the lines the same? Overlaying the papers will show variations in the lines. 4.How could you use the original paper to draw exact copies of the line without tracing it? Possible answer: Cut along the line and use it as a template to draw the line on another sheet of paper. 5.Why is it important that the copies of DNA that are given to new daughter cells be exact copies of the original? Each cell must have the correct DNA, or the cell will not have the correct characteristics.

Section 3 Answers Interest Grabber Answers 1. Why do you think the library holds some books for reference only? Possible answers: The books are too valuable to risk loss or damage to them. The library wants to make sure the information is always available and not tied up by one person. 2. If you can’t borrow a book, how can you take home the information in it? Students may suggest making a photocopy or taking notes. 3. All of the parts of a cell are controlled by the information in DNA, yet DNA does not leave the nucleus. How do you think the information in DNA might get from the nucleus to the rest of the cell? Students will likely say that the cell has some way to copy the information without damaging the DNA.

Section 4 Answers Interest Grabber Answers 1.Copy the following information about Protein X: Methionine—Phenylalanine— Tryptophan—Asparagine—Isoleucine—STOP. 2.Use Figure 12–17 on page 303 in your textbook to determine one possible sequence of RNA to code for this information. Write this code below the description of Protein X. Below this, write the DNA code that would produce this RNA sequence. Sequences may vary. One example follows: Protein X: mRNA: AUG-UUU-UGG-AAU- AUU-UGA; DNA: TAC-AAA-ACC-TTA-TAA-ACT 3.Now, cause a mutation in the gene sequence that you just determined by deleting the fourth base in the DNA sequence. Write this new sequence. (with deletion of 4th base U) DNA: TAC-AAA-CCT-TAT-AAA-CT 4.Write the new RNA sequence that would be produced. Below that, write the amino acid sequence that would result from this mutation in your gene. Call this Protein Y. mRNA: AUG-UUU-GGA-AUA-UUU-GA Codes for amino acid sequence: Methionine— Phenylalaine—Glycine—Isoleucine—Phenylalanine—? 5.Did this single deletion cause much change in your protein? Explain your answer. Yes, Protein Y was entirely different from Protein X.

Section 5 Answers Interest Grabber Answers 1.Do you think that cells produce all the proteins for which the DNA (genes) code? Why or why not? How do the proteins made affect the type and function of cells? Cells do not make all of the proteins for which they have genes (DNA). The structure and function of each cell are determined by the types of proteins present. 2.Consider what you now know about genes and protein synthesis. What might be some ways that a cell has control over the proteins it produces? There must be certain types of compounds that are involved in determining what types of mRNA transcripts are made and when this mRNA translates at the ribosome. 3.What type(s) of organic compounds are most likely the ones that help to regulate protein synthesis? Justify your answer. The type of compound responsible is probably a protein, specifically enzymes, because these catalyze the chemical reactions that take place.