Question 1

Which of the following characteristics is NOT one of the five essential properties of hereditary material identified before DNA was known to be the hereditary molecule?

Accepted Answer

It must be able to catalyze metabolic reactions in the cell.

Question 2

In the classic Hershey-Chase experiment, which radioactive isotope was used to label DNA, and what was the key finding regarding the location of radioactivity after infection?

Accepted Answer

Phosphorus-32 ($^{32}P$); radioactivity was found inside the infected bacteria.

Question 3

Which of the following best describes the antiparallel nature of DNA strands in the double helix?

Accepted Answer

One strand runs 5' to 3', while the other runs 3' to 5'.

Question 4

A scientist is studying a DNA molecule with a high proportion of guanine and cytosine. Which of the following statements about the stability of this DNA is correct?

Accepted Answer

It will be more stable due to the presence of three hydrogen bonds between G and C.

Question 5

Which enzyme is responsible for relieving torsional stress and supercoiling during DNA replication?

Accepted Answer

DNA topoisomerase

Question 6

During DNA replication in E. coli, which enzyme removes RNA primers and replaces them with DNA nucleotides?

Accepted Answer

DNA polymerase I

Question 7

Which of the following best explains why the lagging strand is synthesized discontinuously?

Accepted Answer

DNA polymerase can only add nucleotides to the 3' end, so synthesis must occur in short fragments as the replication fork opens.

Question 8

A mutation in the gene encoding the sliding clamp protein in E. coli would most likely result in which of the following?

Accepted Answer

Decreased processivity of DNA polymerase III, leading to frequent dissociation from the template.

Question 9

Which of the following statements about telomerase is correct?

Accepted Answer

It extends the 3' end of the template strand using an RNA template that is part of the enzyme.

Question 10

In the Meselson-Stahl experiment, after two rounds of DNA replication in $^{14}N$ medium, what was the observed distribution of DNA densities?

Accepted Answer

Half the DNA was intermediate ($^{15}N/^{14}N$), and half was light ($^{14}N/^{14}N$).

Question 11

Which of the following is a key difference between Sanger (dideoxy) sequencing and next-generation sequencing (NGS) technologies?

Accepted Answer

NGS can sequence millions of DNA fragments in parallel, while Sanger sequencing is limited to one fragment per reaction.

Question 12

A researcher is designing a PCR experiment. Which of the following is NOT required for a successful PCR reaction?

Accepted Answer

DNA ligase

Question 13

Which of the following best describes the function of DNA ligase during DNA replication?

Accepted Answer

It seals nicks in the sugar-phosphate backbone between adjacent Okazaki fragments.

Question 14

Which of the following is a consensus sequence function at the origin of replication in E. coli (oriC)?

Accepted Answer

It is recognized and bound by DnaA to initiate strand separation.

Question 15

Which of the following best explains why DNA polymerase requires an RNA primer to begin synthesis?

Accepted Answer

DNA polymerase can only add nucleotides to an existing 3' hydroxyl group.

Question 16

A patient is found to have a mutation that inactivates the 3' to 5' exonuclease activity of DNA polymerase. What is the most likely consequence?

Accepted Answer

Increased mutation rate due to loss of proofreading during DNA replication.

Question 17

Which of the following statements about the major and minor grooves of DNA is correct?

Accepted Answer

They are regions where DNA-binding proteins can make direct contact with nucleotides.

Question 18

Which of the following is a real-world application of variable number tandem repeats (VNTR) analysis?

Accepted Answer

Forensic identification and paternity testing

Question 19

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

Accepted Answer

The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments.

Question 20

Which of the following statements about telomeres and aging is supported by current research?

Accepted Answer

Telomere shortening in somatic cells is associated with cellular aging and the Hayflick limit.

7. DNA Structure and Replication

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