AP Biology



Chapter 9 – DNA Structure and Replication

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OBJECTIVES

• Explain why researchers originally thought protein was the genetic material.

• Summarize experiments performed by scientists, which provided evidence that DNA is the genetic material.

o Frederick Griffith

o Avery and MacLeod

o Alfred Hershey and Martha Chase

• Summarize four key features of the DNA molecule.

• Summarize the four key functions of any genetic material and discuss how the structure of DNA fits each of these functions.

• List the three components of a nucleotide.

• Distinguish between deoxyribose and ribose.

• List the nitrogenous bases found in DNA, and distinguish between pyrimidine and purine.

• Explain the data supporting and the significance of Chargaff’s rules.

• Explain how Watson and Crick deduced the structure of DNA, and describe what evidence they used.

• Describe the structure of DNA, and explain what kind of chemical bond connects the nucleotides of each strand and what type of bond holds the two strands together.

• Explain, in your own words, the semiconservative replication model and describe the Messelson-Stahl experiment.

• Describe the process of DNA replication, and explain the role of helicase, single strand binding protein, DNA polymerase, ligase, and primase.

• Explain what energy source drives endergonic synthesis of DNA>

• Define antiparallel, and explain why continuous synthesis of both DNA strands is not possible.

• Distinguish between the leading and lagging strands.

• Explain how the lagging strand is synthesized when DNA polymerase can add nucleotides only to the 3’ end.

• Summarize the differences between prokaryotic and eukaryotic DNA replication.

• Explain the role of DNA polymerase, ligase, and repair enzymes in DNA proofreading and repair.

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Go to the website . Here you will find an excellent series of tutorials for Chapters 10-16 of our book. Explore panels 8-15 to guide you through this chapter. Be sure to click on the animation and problem links to get the complete info.

1. List the properties a material must contain in order to function as the vector for hereditary information.

2. Review Panel 15 from the website given above and use the information provided here to explain why scientists believed protein was the most likely candidate for passing on hereditary info.

3. Why did DNA appear to be an unlikely candidate for containing hereditary information.

4. The following questions refer to the experiments of Hershey and Chase (the Blender Experiment).

a. What are bacteriophages?

b. Describe the composition of the T2 bacteriophage.

c. What effect does the T2 phage have on E. coli?

d. In one experiment, they grew T2 phages and E. coli in media with radioactive sulfur (35S). Into what phage component was the 35S incorporated?

The phages with the 35S were then allowed to infect E. coli free of 35S. After a period of time, the culture was blended, centrifuged, and analyzed to determine where the location of the 35S in the mixture.

Where was the 35S located in the centrifuged mixture?

What conclusion did they reach based on these results?

e. In another experiment, they grew T2 phages and E.coli in media with radioactive phosphorus (32P). After a period of time, the culture was blended, centrifuged, and analyzed to determine where the location of the 32P in the mixture.

Where was the 32P located in the centrifuged mixture?

What conclusion did they reach based on these results?

5. What three scientist’s worked out the structure of the DNA molecule?

6. What technique was used to determine the structure? Briefly describe the technique. What is causing the x-rays to diffract?

7. The building blocks of DNA are called:

8. Draw a nucleotide, point out the phosphate, sugar and the base. Indicated where the base is a purine or a pyrimidine and whether the nucleotide is from DNA or RNA.

9. The nitrogenous bases found in the DNA are classified into two groups. Identify each of the following examples and/or characteristics as true of Purines or Pyrimidines.

__________ 6-membered ring of carbon and nitrogen atoms

__________ 5-membered ring fused with a 6-membered ring

__________ guanine

__________ adenine

__________ thymine

__________ cytosine

10. What does complementary base pairing mean?

11. Draw a diagram of DNA, point out the 5’ and 3’ ends of each chain. Also point out an individual nucleotide, and its three components. Indicate the type of chemical bond that connects nucleotides within a strand and the type of chemical bond that connects opposing nucleotides across strands.

12. How many hydrogen bonds are formed between:

a. Cytosine and guanine

b. Thymine and adenine

13. Why does adenine pair with thymine and not cytosine?

14. Given the sequence of bases in one strand of DNA is atcgaacgt, give the sequence of the complimentary strand.

15. DNA replication is semiconservative. What does this mean?

16. Listed below are the steps in DNA replication. Put the steps in the correct order.

__________ DNA polymerase adds nucleotides to the exposed bases

__________ DNA ligase joins the Okazaki fragments on the lagging strand

__________ Primase (RNA polymerase) synthesizes the RNA primer

__________ Helicases unwind the DNA double helix

__________ Single-stranded binding proteins stabilize the unwound DNA

17. Match the role/function with the correct molecule.

A. DNA ligase B. DNA Polymerase

C. Helicase D. Okazaki fragments

E. Primase (RNA polymerase) F. RNA primer

G. Single-strand binding proteins

__________ Unwind and unzip DNA

__________ Keep DNA strands separated

__________ Adds DNA nucleotides to exposed bases

__________ Short RNA segment needed to start DNA replication

__________ Fuses the Okazaki fragments

__________ Replication fragments of the lagging strand

18. Why must an RNA polymerase lay down an RNA primer?

19. How does the synthesis of the leading strand differ from that of the lagging strand?

20. Use the diagram at the right to answer the following questions.

a. Which letter (a, b, c, or d) indicates the 5’ end of the DNA strand?

b. At which letter would the next nucleotide be added?

21. In what direction is DNA synthesized?

22. What is a telomere?

23. What is the significance of the telomeres?

24. Describe the differences in DNA replication between prokaryotes and eukaryotes.

|Prokaryotes |Eukaryotes |

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25. What might result from a replication error?

26. What is proofreading? Why is the replication process a source of few mutations?

27. What are some differences between germline and somatic mutations?

28. Summarize the various phenotypic effects that may result from mutations.

29. What are other causes of DNA mutations besides replication errors?

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