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There are several aspects of DNA polymerases that tell you about their probable functions in the cell. These are processivity, 3' -> 5' exonuclease acitvity, requirements for viability, 5' -> 3' exonuclease activity. Describe what each of these mean and indicate what they tell you about the polymerase.

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Patrina Schowalter
Patrina SchowalterLv2
28 Sep 2019

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Related questions

The DNA of bacteriophage l is a linear double-stranded molecule that has complementary single-stranded ends. These molecules can form closed circular molecules when two “cohesive” ends on the same molecule join, and they can form linear dimers, trimers, or longer molecules when sites on different molecules are joined.

a) What conditions should be chosen to ensure that l phage DNA molecules form closed circular monomers, as opposed to dimers, trimers, etc?

b) Under certain, l phage DNA molecules are infective. When a very low concentration of l phage DNA is incubated with DNA polymerase I and the four deoxyribonucleoside triphosphates, the infectious activity of l phage DNA is destroyed. Brief treatment of l phage DNA with bacterial exonuclease III, an enzyme that removes 5’-mononucleotides from the 3’-ends of double-stranded DNA molecules, also destroys infectivity, but subsequent treatment of the DNA with DNA polymerase and nucleotide substrates can restore infectivity. What does this tell you about the structure of the cohesive ends of the DNA? Explain the effects of the two enzymes.

1. (10 points) What are the three enzymatic activities of DNA pol I? What is the role of each activity in the cell during DNA replication?

2. (10 points) DNA polymerase I, DNA ligase, and Topoisomerase I each catalyze the formation of phosphodiester bonds that are vital (directly or indirectly) to replication of DNA. What is the action of each of these enzymes in DNA replication and which part of replication do these enzymes participate in?

3. (10 points) The B-DNA helix undergoes a complete turn every 10.4 nucleotides, and the axial distance between nucleotides is 3.4 angstroms. DNA polymerase III has a rate of 1000 nucleotides per second. How fast does template DNA spin (expressed in revolutions per second) at an E. coli replication fork? What is the velocity of movement (in micrometers per second) of DNA polymerase III holoenzyme relative to the template?

4. (10 points) In contrast to DNA polymerase, RNA polymerase does not proofread and edit its products. Why does this absence of proofreading/correction in the synthesis of RNA not threaten the cells’ viability? How would an enzyme using RNA as a template for DNA synthesis alter the rate of mutations for an organism?

Imagine that you have a strain of bacteria that has a loss-of-function mutation in the adenine methylase gene, which normally adds methyl groups to A's within a GATC sequence on DNA beginning several minutes after the completion of a replication cycle. What effects would you predict to the following aspects of cell function as a result of this? Briefly explain each answer.

1. Ability to repair UV-induced lesions
2. Proofreading activity of DNA polymerase
3. Overall error rate in DNA passed on to daughter cells

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