17. Mutation, Repair, and Recombination

DNA Repair

Open Question
Write a short essay contrasting how these concepts may differ between bacteria and eukaryotes.
Open Question
Answer the following questions concerning the accuracy of DNA polymerase during replication.

Identify two mechanisms that can correct the kind of abnormality resulting from the circumstances identified in part (c).
Open Question
Answer the following questions concerning the accuracy of DNA polymerase during replication.

If a DNA replication error is detected by DNA polymerase, how is it corrected?
Open Question
Answer the following questions concerning the accuracy of DNA polymerase during replication.

DNA mismatch repair can accurately distinguish between the template strand and the newly replicated strand of a DNA duplex. What characteristic of DNA strands is used to make this distinction?
Open Question
Answer the following questions concerning the accuracy of DNA polymerase during replication.

If the kind of abnormality identified in part (c) is not corrected before the next DNA replication cycle, what kind of mutation occurs?
Open Question
Answer the following questions concerning the accuracy of DNA polymerase during replication.

If a replication error escapes detection and correction, what kind of abnormality is most likely to exist at the site of replication error?
Open Question
Answer the following questions concerning the accuracy of DNA polymerase during replication.

What general mechanism do DNA polymerases use to check the accuracy of DNA replication and identify errors during replication?
Open Question
DNA damage brought on by a variety of natural and artificial agents elicits a wide variety of cellular responses involving numerous signaling pathways. In addition to the activation of DNA repair mechanisms, there can be activation of pathways leading to apoptosis (programmed cell death) and cell-cycle arrest. Why would apoptosis and cell-cycle arrest often be part of a cellular response to DNA damage?
Open Question
Contrast the various types of DNA repair mechanisms known to counteract the effects of UV radiation. What is the role of visible light in repairing UV-induced mutations?
Open Question
A 1-mL sample of the bacterium E. coli is exposed to ultraviolet light. The sample is used to inoculate a 500-mL flask of complete medium that allows growth of all bacterial cells. The 500-mL culture is grown on the benchtop, and two equal-size samples are removed and plated on identical complete-medium growth plates. Plate 1 is immediately wrapped in a dark cloth, but plate 2 is not covered. Both plates are left at room temperature for 36 hours and then examined. Plate 2 is seen to contain many more growing colonies than plate 1. Thinking about DNA repair processes, how do you explain this observation?
Open Question
A strain of E. coli is identified as having a null mutation of the RecA gene. What biological property do you expect to be absent in the mutant strain? What is the molecular basis for the missing property?
Open Question
It has been shown that infectious agents such as viruses often exert a dramatic effect on their host cell's genome architecture. In many cases, viruses induce methylation of host DNA sequences in order to enhance their infectivity. What specific host gene functions would you consider as strong candidates for such methylation by infecting viruses?
Open Question
Xeroderma pigmentosum (XP) is an autosomal recessive condition characterized by moderate to severe sensitivity to ultraviolet (UV) light. Patients develop multiple skin lesions on UV-exposed skin, and skin cancers often develop as a result. XP is caused by deficient repair of DNA damage from UV exposure.Many genes are known to be involved in repair of UV-induced DNA damage, and several of these genes are implicated in XP. What genetic phenomenon is illustrated by XP?
Open Question
You have identified five genes in S. cerevisiae that are induced when the yeast are grown in a high-salt (NaCl) medium. To study the potential roles of these genes in acclimation to growth in high-salt conditions, you wish to examine the phenotypes of loss- and gain-of-function alleles of each.How would your answer differ if you were working with tomato plants instead of yeast?
Open Question
You have identified five genes in S. cerevisiae that are induced when the yeast are grown in a high-salt (NaCl) medium. To study the potential roles of these genes in acclimation to growth in high-salt conditions, you wish to examine the phenotypes of loss- and gain-of-function alleles of each.How will you do this?