Question 1

Which enzyme is responsible for the flash of light observed during pyrosequencing, and what is the chemical reaction that produces this light?

Accepted Answer

Luciferase; reaction of pyrophosphate ($$PP_i) $$with luciferin

Question 2

During which phase of the cell cycle does DNA replication occur, and what is the change in DNA content per nucleus after this phase?

Accepted Answer

S phase; DNA content doubles

Question 3

A group of cells is measured for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. How many picograms would be found at the end of S and the end of G2, respectively?

Accepted Answer

16; 16

Question 4

Which experiment demonstrated that DNA replication is semiconservative, and what was the key evidence?

Accepted Answer

Meselson-Stahl experiment; intermediate density DNA after one generation in $$^{14}N$$

Question 5

What is the primary function of topoisomerase during DNA replication?

Accepted Answer

Relieving tension generated ahead of the replication fork

Question 6

Why does DNA polymerase require an RNA primer to initiate DNA synthesis?

Accepted Answer

DNA polymerase can only add nucleotides to an existing chain with a free 3' OH group

Question 7

Which direction does DNA polymerase synthesize new DNA, and what is the mechanistic reason for this directionality?

Accepted Answer

5' to 3'; DNA polymerase can only add nucleotides to a free 3' OH group

Question 8

What is the role of DNA ligase during DNA replication?

Accepted Answer

Joining Okazaki fragments on the lagging strand

Question 9

Which protein protects single-stranded DNA from degradation during replication?

Accepted Answer

Single-stranded DNA binding protein (SSB)

Question 10

Why are Okazaki fragments formed during DNA replication?

Accepted Answer

The lagging strand is synthesized discontinuously in the opposite direction of the replication fork

Question 11

What is the function of the 3' to 5' exonuclease activity of DNA polymerase?

Accepted Answer

Proofreading and removing incorrectly incorporated nucleotides

Question 12

What problem occurs at the ends of linear chromosomes during DNA replication, and which enzyme solves this problem?

Accepted Answer

Loss of telomeric DNA; telomerase extends telomeres

Question 13

Which phase of the cell cycle is highly variable in length and is associated with cell growth and preparation for DNA replication?

Accepted Answer

G1 phase

Question 14

What is the function of BLAST (Basic Local Alignment Search Tool) in bioinformatics?

Accepted Answer

To search for homologous sequences in DNA or protein databases

Question 15

Which type of topoisomerase introduces transient single-strand breaks in DNA to relax supercoils?

Accepted Answer

Type I topoisomerase

Question 16

In eukaryotic cells, what is the significance of multiple replicons during DNA replication?

Accepted Answer

They enable simultaneous replication at multiple origins, speeding up the process

Question 17

Which phase of the cell cycle is associated with permanent exit from the cycle, such as in terminally differentiated neurons?

Accepted Answer

G0 phase

Question 18

What is the effect of extensive supercoiling on DNA structure?

Accepted Answer

It makes DNA more compact

Question 19

Which enzyme is responsible for removing RNA primers during DNA replication?

Accepted Answer

DNA polymerase with 5' to 3' exonuclease activity

Question 20

Why are there no Okazaki fragments in PCR amplification?

Accepted Answer

There are no replication forks in a PCR reaction

DNA Replication and the Eukaryotic Cell Cycle: Mechanisms and Regulation

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