Study Guide 12
Last revised: Thursday, October 11, 2001
Topic: DNA
Replication
Chapter 16- Scientists knew that chromosomes carried genes as early as 1905. Why did it take until 1953 for the structure of DNA to be understood?
- Explain what each of the following scientists contributed to the “story of DNA”: (a) Griffith, (b) Avery et al, (c) Hershey & Chase, (d) Chargaff, (e) Watson & Crick
- Review the basic structure and nomenclature for nucleotides, including: which bases are purines, which bases are pyrimidines, difference between ribose and deoxyribose, variety of mono-, di-, and tri-phosphate forms. What is the difference between dATP and ATP, for example? Between CMP and dCDP?
- How many phosphates are present in the nucleotides from which DNA is synthesized? How many phosphate molecules are present per nucleotide in a DNA chain?
- Identify the role of each of the following proteins in DNA replication: DNA polymerase, helicase, DNA primase, DNA ligase, Okazaki fragments. (see Fig. 16.16).
- What is meant by “antiparallel strands” in DNA? What restriction does this place on replication?
- Note that, because the energy for adding new nucleotides to DNA comes from hydrolysis of phosphate bonds, it is only possible to add new nucleotides to a DNA (or RNA) strand at its 3’–terminus. Thus all growth of nucleic acids occurs at the 3’-end; another way of saying this is that new DNA (and RNA) chains are synthesized in the 5’ to 3’ direction. Using this fact, explain what is meant by a “lagging strand” in DNA replication. What is meant by “leading strand”.
- DNA polymerase enzymes also carry out proofreading and repair functions, including the excision of incorrectly paired bases and reinsertion of new DNA -- see fig. 16.17. What is the sequence of steps needed to accomplish "excision repair"? How many enzymes are needed? Name them.
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