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 add nucleotides to the 3’ end, and the lagging strand template is oriented 5’ to 3’ relative to the fork movement.

Question 3

Which of the following best describes the catalytic mechanism of DNA polymerase during DNA synthesis?

Accepted Answer

The 3’OH of the growing strand attacks the α-phosphate of the incoming dNTP, facilitated by two Mg2+ ions.

Question 4

What is the primary function of the 3’→5’ exonuclease activity of DNA polymerases?

Accepted Answer

Proofreading newly synthesized DNA by removing mismatched nucleotides.

Question 5

Which enzyme is responsible for removing RNA primers and replacing them with DNA nucleotides during E. coli DNA replication?

Accepted Answer

DNA polymerase I

Question 6

Why do eukaryotic chromosomes require telomerase for complete replication?

Accepted Answer

Because removal of the last RNA primer at the 5’ end leaves a gap that cannot be filled by DNA polymerase.

Question 7

Which of the following statements about the directionality of DNA synthesis is correct?

Accepted Answer

DNA synthesis always occurs in the 5’ to 3’ direction.

Question 8

A mutation in the gene encoding the β sliding clamp of DNA polymerase III 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 9

Which laboratory technique relies on the principle of DNA denaturation and renaturation to amplify specific DNA sequences?

Accepted Answer

Polymerase Chain Reaction (PCR)

Question 10

What is the significance of the ‘hypochromic effect’ in double-stranded DNA?

Accepted Answer

Double-stranded DNA absorbs less UV light at 260 nm due to base stacking interactions.

Question 11

Which of the following best explains why multiple origins of replication are necessary in eukaryotic chromosomes?

Accepted Answer

Eukaryotic chromosomes are much larger and DNA polymerases are slower, so multiple origins ensure timely replication.

Question 12

A scientist is measuring the concentration of a DNA solution using absorbance at 260 nm. If the measured $$A_{260} is 0.5 in a 1 cm $$path-length cuvette, what is the concentration of double-stranded DNA in the solution?

Accepted Answer

$$25\ \mu g/mL$$

Question 13

Which of the following is a direct consequence of the end-replication problem in eukaryotic cells lacking telomerase?

Accepted Answer

Progressive shortening of chromosome ends with each cell division.

Question 14

Which property of DNA polymerase ensures that only correctly base-paired nucleotides are incorporated during DNA synthesis?

Accepted Answer

High fidelity of the active site, which excludes incorrect base pairs.

Question 15

In the context of DNA replication, what is the role of DNA ligase?

Accepted Answer

It forms phosphodiester bonds to seal nicks between adjacent Okazaki fragments.

Question 16

Which of the following statements about telomerase is correct?

Accepted Answer

Telomerase is a reverse transcriptase that uses its own RNA template to extend the 3’ end of DNA.

Question 17

A mutation that inactivates the 5’→3’ exonuclease activity of DNA polymerase I in E. coli would most directly affect which process?

Accepted Answer

Removal of RNA primers from Okazaki fragments.

Question 18

Which of the following best describes the function of single-strand binding proteins (SSB) during DNA replication?

Accepted Answer

They stabilize separated DNA strands and prevent them from re-annealing.

Question 19

Which of the following is NOT a direct application of DNA denaturation and renaturation in the laboratory?

Accepted Answer

Protein purification by affinity chromatography.

DNA Replication: Mechanisms, Enzymes, and Laboratory Applications

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