Question 1

Which experimental result from the Meselson-Stahl experiment provided the strongest evidence for the semiconservative model of DNA replication?

Accepted Answer

The appearance of a single band of intermediate density after one round of replication in 14N medium.

Question 2

During DNA replication, why is the lagging strand synthesized discontinuously?

Accepted Answer

Because DNA polymerase can only synthesize DNA in the 5' to 3' direction, and the lagging strand template is oriented 5' to 3' relative to the fork movement.

Question 3

What is the primary function of the 5' to 3' exonuclease activity of E. coli DNA polymerase I during DNA replication?

Accepted Answer

To remove RNA primers from Okazaki fragments and replace them with DNA nucleotides.

Question 4

Which of the following best describes the role of Mg$$^{2+}$$ ions in the catalytic activity of DNA polymerases?

Accepted Answer

They stabilize the transition state and facilitate the nucleophilic attack of the 3'-OH on the $$b-$$phosphate of the incoming dNTP.

Question 5

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 DNA template.

Question 6

Why do eukaryotic chromosomes require multiple origins of replication?

Accepted Answer

Because eukaryotic genomes are much larger and their DNA polymerases are slower than those in prokaryotes.

Question 7

What is the main reason for the progressive shortening of eukaryotic chromosomes after each round of DNA replication?

Accepted Answer

The inability of DNA polymerase to fill the gap left after removal of the last RNA primer at the 5' end of the new strand.

Question 8

Which of the following statements about telomerase is TRUE?

Accepted Answer

Telomerase is a reverse transcriptase that extends the 3' end of the parental DNA strand using its own RNA template.

Question 9

Which laboratory technique relies on the principle that DNA absorbs UV light maximally at 260 nm?

Accepted Answer

Quantification of DNA or RNA concentration in solution.

Question 10

A scientist is using PCR to amplify a gene from a small DNA sample. Which property of Taq DNA polymerase makes it especially suitable for this technique?

Accepted Answer

It is thermostable and does not denature at high temperatures used during the denaturation step.

Question 11

Which of the following best explains the 'hypochromic effect' observed in double-stranded DNA?

Accepted Answer

Base stacking interactions in the double helix reduce UV absorbance compared to single-stranded DNA.

Question 12

Which enzyme is responsible for joining Okazaki fragments on the lagging strand during DNA replication?

Accepted Answer

DNA ligase

Question 13

A mutation eliminates the 3' to 5' exonuclease activity of DNA polymerase III in E. coli. What is the most likely consequence?

Accepted Answer

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

Question 14

Which of the following is a direct application of DNA denaturation and renaturation in molecular biology?

Accepted Answer

Hybridization of labeled DNA probes to detect specific sequences.

Question 15

Which of the following best describes the directionality of DNA synthesis by DNA polymerases?

Accepted Answer

DNA is always synthesized in the 5' to 3' direction.

Question 16

Which of the following is NOT a function of single-strand binding proteins (SSB) during DNA replication?

Accepted Answer

Catalyzing the formation of phosphodiester bonds between nucleotides.

Question 17

Which of the following statements about the Polymerase Chain Reaction (PCR) is CORRECT?

Accepted Answer

PCR requires synthetic DNA primers that flank the target DNA sequence.

Question 18

Which of the following is a unique feature of eukaryotic DNA replication compared to prokaryotic DNA replication?

Accepted Answer

The presence of telomerase to maintain chromosome ends.

Question 19

Which of the following best explains why telomerase activity is often detected in cancer cells?

Accepted Answer

It allows for the maintenance of telomere length during continuous cell divisions.

DNA Replication: Mechanisms, Enzymes, and Laboratory Applications

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