GRE Subject Test: Biology : Understanding DNA Repair

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #8 : Dna Replication And Repair

Which of the following is not true of DNA repair?

Possible Answers:

Irreparable DNA damage may activate pathways that lead to apoptosis

Several DNA polymerases contain an exonuclease function 

DNA repair cannot occur during replication

p53 is a protein responsible for activating many DNA repair pathways

Correct answer:

DNA repair cannot occur during replication

Explanation:

DNA repair can, and does, occur during replication. An easy example of this is the proofreading function of several DNA polymerases. This function is carried out due to the enzymes containing an exonuclease function that allows them to excise incorrect base pairs. p53 is an incredibly important protein that is expressed heavily when DNA damage is detected. It is responsible for activating both DNA repair pathways and apoptotic pathways, preventing the cell from passing replication and cell cycle checkpoints. If the DNA damage is irreparable, the cell may undergo apoptosis. 

Example Question #1 : Understanding Dna Repair

Upon double-stranded DNA break, the cell can search the genome for a homologous sequence to serve as a template for repairing the damaged sequence. What is this process known as?

Possible Answers:

Base excision repair

Crossing over 

Directed reversal

Non-homologous end joining

Homology directed repair

Correct answer:

Homology directed repair

Explanation:

The correct answer is homology directed repair. Using flanking homologous regions upstream and downstream of the double stranded break, the cell is able to determine the precise sequence that is in the damaged region and repair that sequence. 

Example Question #2 : Understanding Dna Repair

Which of the following enzymes is responsible for catalyzing the formation of phosphodiester bonds in single- and double-stranded DNA breaks?

Possible Answers:

DNA ligase

DNA polymerase I

Endonuclease

DNA polymerase III

Exonuclease 

Correct answer:

DNA ligase

Explanation:

DNA ligase catalyzes the formation of phosphodiester bonds between the elements of the DNA backbone. DNA polymerases function in replication of DNA, whereas exonucleases and endonucleases break apart DNA strands by disrupting phosphodiester bonds. 

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