Question 1

Which enzyme is primarily responsible for relieving torsional strain during DNA replication by introducing transient single-strand breaks?

Accepted Answer

Type I topoisomerase

Question 2

What is the main reason that linear chromosomes require telomerase for complete replication?

Accepted Answer

The lagging strand cannot be fully replicated at the 3' end, leading to progressive shortening.

Question 3

Which of the following best describes DNA supercoiling?

Accepted Answer

The coiling of a closed duplex DNA in space so that it crosses over its own axis.

Question 4

A researcher observes that a plasmid migrates faster on an agarose gel after treatment with a certain enzyme. Which enzyme was most likely used?

Accepted Answer

Restriction endonuclease that linearizes the plasmid

Question 5

Which of the following statements about the linking number (Lk) of DNA is correct?

Accepted Answer

Lk is the sum of twist and writhe in closed circular DNA.

Question 6

What is the role of the RNA component (TERC) in telomerase activity?

Accepted Answer

It serves as a template for the addition of telomeric repeats.

Question 7

Which of the following best explains why DNA in cells is typically negatively supercoiled?

Accepted Answer

Negative supercoiling facilitates local unwinding required for processes like replication and transcription.

Question 8

A mutation in the gene encoding telomerase leads to rapid telomere shortening in somatic cells. Which of the following is a likely consequence?

Accepted Answer

Premature cellular senescence

Question 9

Which of the following equations correctly relates the linking number (Lk), twist (Tw), and writhe (Wr) of a closed circular DNA molecule?

Accepted Answer

$$Lk = Tw + Wr$$

Question 10

Which enzyme is capable of introducing double-strand breaks in DNA to manage supercoiling and untangle DNA during replication?

Accepted Answer

Type II topoisomerase

Question 11

During aging, telomeres shorten with each cell division. What is the most direct molecular reason for this phenomenon?

Accepted Answer

DNA polymerase cannot replicate the very end of the lagging strand due to the removal of the RNA primer.

Question 12

Which of the following best describes the action of Type I topoisomerase?

Accepted Answer

It introduces transient single-strand breaks to relieve supercoiling.

Question 13

A circular DNA molecule has a linking number ($$Lk) of 200$$, a twist ($$Tw) of 190. $$What is the writhe ($$Wr$$)?

Accepted Answer

$$Wr = 10$$

Question 14

Which of the following is a direct consequence of telomerase deficiency in stem cells?

Accepted Answer

Progressive loss of genetic information at chromosome ends

Question 15

Which of the following best explains why supercoiled DNA migrates faster than linear DNA in agarose gel electrophoresis?

Accepted Answer

Supercoiled DNA is more compact, allowing it to move more easily through the gel matrix.

Question 16

Which of the following is NOT a function of topoisomerases?

Accepted Answer

Extending telomeres

Question 17

A patient’s cells show critically short telomeres and increased chromosomal instability. Which enzyme is most likely defective?

Accepted Answer

Telomerase

Question 18

Which of the following best describes the mechanism by which telomerase extends the 3’ end of chromosomes?

Accepted Answer

It uses an internal RNA template to add DNA repeats to the 3’ overhang.

Question 19

Which of the following is a plausible outcome if Type II topoisomerase is inhibited during DNA replication?

Accepted Answer

Accumulation of positive supercoils ahead of the replication fork, leading to replication stalling.

DNA Supercoiling and Telomere Replication: Implications for Chromosome Stability

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