Question 1

What process is defective in people with hereditary non-polyposis colon cancer? Explain your answer.

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Question 2

Predict the molecular and phenotypic consequences of loss of strand discrimination by the mismatch repair pathway.

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Question 3

What damage can be caused to DNA by UV irradiation? Describe the key steps of three different mechanisms by which this damage can be repaired. Do all three mechanisms repair the damage accurately? Are all mechanisms active in humans?

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Question 4

How does transcription coupled repair (TCR) differ from global genome repair (GGR)?

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Question 5

What DNA repair system is missing in xeroderma pigmentosum variant (XPV) patients? What is the backup system for lesions missed by the nucleotide excision repair system in XP-V patients?

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Question 6

Compare and contrast repair of double strand breaks by homologous recombination or nonhomologous end-joining. Which is used predominantly in mammalian cells?

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Question 7

Describe experiments that led to the characterization of the Holliday junction resolvasome.

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Question 8

What would be the effect on reading frame and gene function if: (a) Two nucleotides were inserted into the middle of an mRNA? (b) Three nucleotides were inserted into the middle of an mRNA? (c) One nucleotide was inserted into one codon and one subtracted from the next? (d) A transition mutation occurs from GA during DNA replication? What is the effect after a second round of DNA replication? (d) Exposure to an alkylating agent leads to the formation of O⁶-methylguanine? What is the effect after DNA replication?

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Question 9

A friend of yours with xeroderma pigmentosum seeks your advice about participating in a sun tanning competition in Florida during Spring Break. Provide appropriate advice.

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Question 10

Draw a diagram of a Holliday junction during double-strand break repair. Starting with that diagram, illustrate branch migration and resolution. Is the resulting DNA duplex "repaired" to its original state?

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Question 11

You have isolated a novel protein factor you suspect is essential for efficient mismatch repair in mammalian cells. Design an experiment to test for repair activity in vitro. Show sample positive results.

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Quiz 7: DNA Repair Pathways