Question 1

Which of the following statements best explains why DNA polymerase cannot initiate DNA synthesis on its own during replication?

Accepted Answer

DNA polymerase requires a free 3'-OH group to add nucleotides, which must be provided by a primer.

Question 2

During DNA replication, which enzyme is responsible for relieving the strain caused by the unwinding of the DNA double helix?

Accepted Answer

Topoisomerase

Question 3

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 discontinuously in Okazaki fragments.

Question 4

Which of the following is released as a byproduct during the formation of a phosphodiester bond in DNA synthesis?

Accepted Answer

Pyrophosphate ($$PP_i)$$

Question 5

A patient with xeroderma pigmentosum (XP) is highly sensitive to sunlight. Which DNA repair mechanism is defective in this condition?

Accepted Answer

Nucleotide excision repair

Question 6

Which of the following is NOT a difference between DNA and RNA?

Accepted Answer

DNA contains phosphate groups, while RNA does not.

Question 7

What is the role of single-strand binding proteins during DNA replication?

Accepted Answer

They prevent single-stranded DNA from reannealing.

Question 8

Which enzyme removes RNA primers and replaces them with DNA during lagging strand synthesis?

Accepted Answer

DNA polymerase I

Question 9

A mutation causes DNA polymerase III to lose its 3'→5' exonuclease activity. What is the most likely consequence?

Accepted Answer

The error rate during DNA replication will increase.

Question 10

Which of the following best explains why the loss of pyrophosphate ($$PP_i) $$during DNA polymerization is important?

Accepted Answer

It provides the energy needed to form the phosphodiester bond.

Question 11

In E. coli, how does the mismatch repair system distinguish the newly synthesized DNA strand from the template strand?

Accepted Answer

The template strand is methylated, while the new strand is not yet methylated.

Question 12

Which of the following is a direct result of UV radiation on DNA?

Accepted Answer

Formation of thymine dimers

Question 13

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

Accepted Answer

It joins Okazaki fragments by sealing nicks in the sugar-phosphate backbone.

Question 14

A scientist is studying a virus with single-stranded DNA as its genetic material. Which of the following statements is correct?

Accepted Answer

Some viruses use single-stranded DNA or RNA as their genetic material.

Question 15

Which of the following is the correct sequence of events in nucleotide excision repair?

Accepted Answer

Detection of distortion → Endonuclease cuts the DNA → DNA polymerase fills the gap → DNA ligase seals the nick

Question 16

Which of the following best explains why Okazaki fragments are shorter in eukaryotes (~100 nt) than in bacteria (~1000 nt)?

Accepted Answer

Eukaryotic DNA is more tightly packed and has more frequent priming events.

Question 17

Which of the following is a real-world consequence of a defect in mismatch repair proteins?

Accepted Answer

Increased mutation rate and higher risk of certain cancers

Question 18

Which of the following best describes the role of hydrogen bonds during DNA replication?

Accepted Answer

They stabilize the pairing of incoming nucleotides with the template strand.

Question 19

A mutation in the gene encoding primase would most directly affect which step of DNA replication?

Accepted Answer

Synthesis of RNA primers required for DNA polymerase to begin synthesis

Question 20

Which of the following is a function of DNA polymerase I during DNA replication?

Accepted Answer

Replacing RNA primers with DNA nucleotides

LEC 19 :DNA Replication and Repair Mechanisms

Study Guide - Practice Questions