Question 1

Which repair pathway requires a set of enzymes that recognize specific chemical modifications to DNA?

Accepted Answer

Base excision repair involves enzymes that recognize and remove specific chemically modified bases, followed by repair of the resulting abasic site.

Question 2

Repair of a DNA double-strand break by homologous recombination is initiated by

Accepted Answer

The Mre11-Rad50-Nbs1 (MRN) complex is crucial for the initiation of DNA double-strand break repair by homologous recombination, as it senses the break and recruits other factors necessary for the repair process.

Question 3

Repair of a DNA double-strand break by nonhomologous end-joining is initiated by

Accepted Answer

Ku70 and Ku80 initiate the repair of a DNA double-strand break by nonhomologous end-joining by first binding to the broken DNA ends, thereby protecting them and recruiting other factors necessary for the repair process.

Question 4

Homologous recombination repairs double-strand breaks by

Accepted Answer

Homologous recombination repairs double-strand breaks by retrieving genetic information from an undamaged homologous chromosome, using it as a template to accurately repair the break.

Question 5

Nonhomologous end-joing repairs double-strand breaks by

Accepted Answer

Nonhomologous end-joining repairs double-strand breaks by directly ligating the broken DNA ends together without the need for a homologous template.

Question 6

The Holliday junction is resolved into two duplexes by an enzyme complex called

Accepted Answer

The resolvasome is the enzyme complex responsible for resolving Holliday junctions, which are crossover structures formed during the process of homologous recombination, into two separate duplex DNA molecules.

Question 7

Explain why high-fidelity DNA replication is not always an advantage.

Accepted Answer

The answer of Explain why high-fidelity DNA replication is not...

Question 8

Diagram how a point mutation changing a GC base pair to a GA base pair can be permanently incorporated by DNA replication.

Accepted Answer

The answer of Diagram how a point mutation changing a...

Question 9

Compare and contrast silent mutations, missense mutations, nonsense mutations, and frameshift mutations.

Accepted Answer

The answer of Compare and contrast silent mutations, missense mutations,...

Question 10

In addition to deploying repair machinery, cells respond to global DNA damage by preventing entry into S phase. Provide a rationale for this observation.

Accepted Answer

The answer of In addition to deploying repair machinery, cells...

Question 11

Draw the structure of a cyclobutane ring between adjacent thymines and explain how formation of thymine-thymine dimers distorts the double helix.

Accepted Answer

The answer of Draw the structure of a cyclobutane ring...

Question 12

Compare and contrast the three major classes of DNA damage.

Accepted Answer

The answer of Compare and contrast the three major classes...

Question 13

Explain why unequal crossing over and DNA slippage results cause the specific problem of trinucleotide repeat expansion rather than random errors. Use diagrams to illustrate your answer.

Accepted Answer

The answer of Explain why unequal crossing over and DNA...

Question 14

Define the term "translesion DNA synthesis" and briefly explain its mechanism.

Accepted Answer

The answer of Define the term "translesion DNA synthesis" and...

Question 15

Explain why translesion synthesis is not truly a repair system.

Accepted Answer

The answer of Explain why translesion synthesis is not truly...

Question 16

What two enzymes catalyze direct reversal of DNA damage? Diagram/briefly explain the mechanisms they use. Are both repair pathways present in human cells?

Accepted Answer

The answer of What two enzymes catalyze direct reversal of...

Question 17

Explain why repair of the methylated base O⁶-methylguanine by methyltransferases is considered very costly to a cell.

Accepted Answer

The answer of Explain why repair of the methylated base...

Question 18

Exposure of DNA to an oxidizing agent leads to the formation of 8-oxoguanine (oxoG). Name the pathway used to repair this damage and describe the two-step model based on X-ray crystallographic analysis for how the damage is first recognized.

Accepted Answer

The answer of Exposure of DNA to an oxidizing agent...

Question 19

What is the mismatch repair system and when is it used? Include the key players of the system and the concept of strand discrimination in your answer.

Accepted Answer

The answer of What is the mismatch repair system and...

Question 20

Describe the "molecular switch model" for MutS's mode of action. Include in your answer the proposed role of ATP.

Accepted Answer

The answer of Describe the "molecular switch model" for MutS's...

Quiz 7: DNA Repair Pathways