GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with DNA Repair Processes

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #18 : Dna Replication And Repair

What is translesion DNA synthesis?

Possible Answers:

A method of DNA synthesis by which a cell may replicate over a mutation encountered on the parental strand 

A method of RNA synthesis used to make highly specialized RNA molecules

A method of DNA synthesis used exclusively for the mitochondrial genome

A method of DNA synthesis used by prokaryotes only

Correct answer:

A method of DNA synthesis by which a cell may replicate over a mutation encountered on the parental strand 

Explanation:

Translesion DNA synthesis is a technique used by both prokaryotes and eukaryotes. The main purpose of translesion DNA synthesis is to bypass lesions encountered during DNA replication (commonly thymine dimers or AP sites). Translesion DNA synthesis is not exclusive to the mitochondria, nor does it create specialized RNA molecules. 

Example Question #19 : Dna Replication And Repair

Which of the following DNA repair mechanisms would be employed by the cell to repair DNA damage from UV light?

Possible Answers:

Direct reversal

Base excision repair

None of these answers are correct

Nucleotide excision repair

Correct answer:

Nucleotide excision repair

Explanation:

UV light causes the formation of thymidine dimers. A thymidine dimer is two thymine molecules that dimerize and cannot be recognized by the DNA transcription machinery, which would cause a mutation in the gene if the dimerization occurs on a gene.

Base excision repair and direct reversal only work on individual bases on the DNA molecule. Nucleotide excision repair cuts out a section of damaged DNA and repolymerizes the molecule, as would be required in this case.

Example Question #20 : Dna Replication And Repair

If a double strand break (DSB) is not repaired during G1 phase of the cell cycle, what type of replication error would result during S phase at the site of the DSB?

Possible Answers:

Reversed replication fork

Gap in the newly replicated DNA strand

Catenane formations

Collapsed replication fork

Correct answer:

Collapsed replication fork

Explanation:

Unrepaired doublestrand breaks will result in collapse of the DNA fork because the replication fork cannot continue beyond the area that has the doublestrand break. The other answers require the presence of at least one continuous strand of DNA.

Example Question #1 : Help With Dna Repair Processes

What term best describes when RNA polymerase binds promoters and synthesizes and releases short mRNA transcripts in cycles before the RNA holoenzyme leaves the  promoter? 

Possible Answers:

DNA scrunching 

Cyclic initiation

Abortive initiation

Promoter clearance

Repressive transcription 

Correct answer:

Abortive initiation

Explanation:

The correct answer is abortive initiation. This is a normal transcription event is found in both prokaryotes and eukaryotes and occurs prior to promoter clearance, or the event when RNA polymerase escapes the promoter and begins elongation of synthesized transcripts. Abortive initiation is thought to occur when the RNA polymerase complex is not stable enough on the DNA. DNA scrunching describes the mechanism by which RNA polymerase transcribes, rather than RNA polymerase moving along DNA, it actually pulls DNA into the complex and unwinds it. 

Example Question #1 : Help With Dna Repair Processes

Branched nucleic acid structures containing 4 double-stranded arms that are intermediates in genetic recombination and DNA repair are best known as? 

Possible Answers:

Pyrimidine dimers

None of these

Spliceosome 

Holliday junction

Replication fork

Correct answer:

Holliday junction

Explanation:

The correct answer is Holliday junction. These intermediates in genetic recombination have symmetrical sequence and are mobile to preserve specific base pairing at recombination and damage loci. Repair enzymes recognize and subsequently localize to this DNA structure to facilitate locus specific enzymatic activity. 

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