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Which statement is not true about the deamination of cytosine?


A) Deamination can occur spontaneously from the action of water
B) Deamination is an example of DNA damage resulting in a single base change.
C) Methylated cytosine is protected from deamination.
D) Deamination converts cytosine to uracil.

E) B) and D)
F) A) and B)

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

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To diagram how a point mutation changing...

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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.

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Mismatch repair occu...

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A transversion mutation is one in which


A) one pyrimidine base is replaced with another, or one purine base with another.
B) one pyrimidine base is replaced with a purine base or vice versa.
C) there is a C to T substitution.
D) there is an A to G substitution.

E) None of the above
F) A) and D)

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The most frequent ultraviolet (UV) light-induced lesions of DNA are


A) oxidation of guanine to generate 8-oxoguanine.
B) formation of a cyclobutane ring between adjacent thymines, forming a thymine dimer.
C) induction of 5-bromouracil.
D) double-strand breaks.

E) B) and C)
F) A) and D)

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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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(a) If two nucleotides were inserted int...

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Nonhomologous end-joing repairs double-strand breaks by


A) direct ligation of DNA ends.
B) DNA synthesis without a template.
C) retrieving genetic information from an undamaged homologous chromosome.
D) translesion synthesis.

E) None of the above
F) A) and B)

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


A) nucleotide excision repair
B) base excision repair
C) mismatch repair
D) non-homologous end joining

E) B) and C)
F) All of the above

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

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Mismatch r...

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

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DNA damage can be transformed into perma...

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

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DNA photolyase (not ...

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A nonsense mutation is one in which:


A) the altered codon codes for the same amino acid.
B) the altered codon codes for a different amino acid.
C) the mutant protein is shorter than normal.
D) insertion or deletion results in a shift in the reading frame.

E) A) and C)
F) None of the above

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

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The repair pathway responsible for recog...

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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.

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The pathway used to repair the damage ca...

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Which statement is not true about the enzyme methyltransferase?


A) A sulfhydryl group of a cysteine residue in the enzyme accepts a methyl group.
B) The enzyme mediates direct reversal of DNA damage.
C) After accepting a methyl group from methylguanine, the enzyme can be used again.
D) The enzyme is present in organisms ranging from E. coli to humans.

E) All of the above
F) A) and B)

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Translesion synthesis is mediated by


A) error-prone DNA polymerases
B) replicative DNA polymerases
C) DNA glycosylase
D) DNA photolyase

E) A) and D)
F) A) and C)

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


A) the Mre11-Rad50-Nbs1 (MRN) complex.
B) the resolvasome.
C) Rad52.
D) BRCA1.

E) B) and C)
F) A) and C)

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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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Xeroderma pigmentosum variant (XPV) pati...

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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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UV irradiation predominantly induces the...

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The disease hereditary nonpolyposis colorectal cancer results from defects in which DNA Repair pathway?


A) nucleotide excision repair
B) base excision repair
C) double-strand break repair
D) mismatch repair

E) A) and B)
F) A) and C)

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