Question 1

Which radioactive isotope did Hershey and Chase use to label viral DNA in their experiment, and why was this isotope chosen?

Accepted Answer

Radioactive phosphorus, because phosphorus is found in DNA but not in protein.

Question 2

During the Hershey-Chase experiment, which result would support the protein hypothesis for the genetic material of viruses?

Accepted Answer

Radioactive protein found in the solution after centrifugation.

Question 3

Which of the following best describes the modern definition of a gene?

Accepted Answer

A segment of DNA that codes for a protein or functional RNA.

Question 4

In an analysis of the nucleotide composition of DNA, which of the following relationships will always be found according to Chargaff's rules?

Accepted Answer

$$A + C = G + T$$

Question 5

What type of bond holds the two strands of a DNA double helix together?

Accepted Answer

Hydrogen bonds

Question 6

During which phase of the cell cycle is DNA replicated?

Accepted Answer

Interphase

Question 7

The leading strand in DNA replication is synthesized _______, and the lagging strand is synthesized _______.

Accepted Answer

$$5' \rightarrow 3'$$; $$5' \rightarrow 3'$$

Question 8

Which enzyme starts DNA synthesis at the 3' end of a primer during replication?

Accepted Answer

DNA polymerase III

Question 9

A student mixes all necessary molecules for DNA replication except one. Replication occurs, but each DNA duplex consists of a normal DNA strand paired with numerous segments of DNA a few hundred nucleotides long. What was missing?

Accepted Answer

DNA ligase

Question 10

During DNA replication, which enzyme removes RNA primers and replaces them with DNA nucleotides?

Accepted Answer

DNA polymerase I

Question 11

Which of the following statements correctly describes the difference between the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short fragments that are ultimately stitched together.

Question 12

During DNA replication, the lagging strand is:

Accepted Answer

Made up of short DNA/RNA fragments

Question 13

Assume the following DNA sequence with a 6-base RNA primer: 
3'-CATATCACTATCATGAGCCTAGCTCAGACTG-5' 
5'-UACUCG-3' 
What new DNA sequence would DNA polymerase add to the bottom strand?

Accepted Answer

5'-GATCGAGTCTGAC-3'

Question 14

Which of the following mechanisms contributes to the low error rate during DNA replication?

Accepted Answer

DNA polymerase proofreading

Question 15

Nucleotide excision repair is responsible for:

Accepted Answer

Recognizing and repairing thymine dimers and other damaged bases in DNA.

Question 16

What aspect of DNA structure allows enzymes of nucleotide excision repair to recognize many different types of DNA damage?

Accepted Answer

The regularity of DNA's overall structure.

Question 17

If a mutation rendered primase non-functional in E. coli, what would happen at the replication fork?

Accepted Answer

No RNA primers would be synthesized, so DNA synthesis would not initiate.

Question 18

The human genome consists of 3 billion base pairs of DNA. DNA replication is highly accurate, resulting in about one mistake per billion nucleotides. For the human genome, how often would errors occur, on average?

Accepted Answer

Once or twice in the lifetime of an individual

Question 19

Which of the following is a real-world consequence of defects in DNA repair pathways?

Accepted Answer

Increased risk of cancer due to accumulation of mutations.

DNA Replication and Repair: Structure, Mechanisms, and Fidelity

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