Question 1

Which of the following best describes the role of the G1 checkpoint in the eukaryotic cell cycle?

Accepted Answer

It verifies sufficient nutrients, growth factors, and absence of DNA damage before allowing entry into S phase.

Question 2

In E. coli, how can the cell divide faster than the time required to replicate its entire genome?

Accepted Answer

By initiating a new round of DNA replication before the previous round is complete, resulting in overlapping replication cycles.

Question 3

Which protein is responsible for binding to the dnaA box and initiating DNA replication in E. coli?

Accepted Answer

DnaA

Question 4

What is the significance of Dam methylation in the regulation of DNA replication initiation in E. coli?

Accepted Answer

It allows DnaA to bind to the origin only when both DNA strands are fully methylated, ensuring proper timing of replication initiation.

Question 5

Which of the following is a consequence of uncoupling DNA replication from the cell cycle in bacteria?

Accepted Answer

Cells become polyploid due to multiple rounds of replication without division.

Question 6

Which checkpoint gene is most commonly mutated in human cancers and acts as a tumor suppressor by inhibiting cell cycle progression?

Accepted Answer

Rb (Retinoblastoma protein)

Question 7

A temperature-sensitive mutant allele in a bacterial cell division gene causes normal phenotype at 30°C but fails to divide at 42°C. What is the most likely explanation?

Accepted Answer

The protein encoded by the gene unfolds and loses function at high temperature.

Question 8

Which of the following best describes the function of the Min proteins in bacterial cell division?

Accepted Answer

They prevent septum formation at the cell poles, ensuring division occurs at mid-cell.

Question 9

What is the role of Ras in cell cycle regulation?

Accepted Answer

It is a small GTPase that activates a kinase cascade, promoting cell proliferation.

Question 10

Which of the following statements about cyclin-dependent kinases (CDKs) is correct?

Accepted Answer

CDKs require binding to cyclins and phosphorylation by CAKs for full activation.

Question 11

A cell with a loss-of-function mutation in p53 fails to arrest the cell cycle in response to DNA damage. What is the most likely outcome?

Accepted Answer

The cell may replicate damaged DNA, increasing the risk of tumorigenesis.

Question 12

Which of the following is true regarding the origin of replication (ori) in eukaryotic chromosomes?

Accepted Answer

There are tens of thousands of ori sites per chromosome, spaced 40-100k bp apart.

Question 13

Which equation best represents the conservative model of DNA replication?

Accepted Answer

$$	ext{Parent DNA} ightarrow 	ext{One molecule with both old strands} + 	ext{One molecule with both new strands}$$

Question 14

Which of the following is an intrinsic limiting factor for the bacterial cell cycle?

Accepted Answer

Time required to replicate the entire genome

Question 15

What is the function of the septum during bacterial cell division?

Accepted Answer

It divides the cell into two daughter cells by forming a new cell wall at mid-cell.

Question 16

Which of the following best explains why newly synthesized DNA in E. coli cannot immediately initiate another round of replication?

Accepted Answer

It is hemimethylated and cannot bind DnaA until fully methylated.

Question 17

Which of the following is a key difference between prokaryotic and eukaryotic cell cycle regulation?

Accepted Answer

Eukaryotes require external signals such as growth factors to initiate division.

Question 18

Which of the following mutations is most likely to result in tumorigenesis?

Accepted Answer

Loss-of-function mutation in a cell cycle repressor gene such as Rb or p53.

Question 19

Which process is responsible for ensuring that the right gene products are made at the right levels, time, and place?

Accepted Answer

Gene regulation

Question 20

Which of the following best describes the bidirectional model of DNA replication?

Accepted Answer

Replication proceeds in both directions from the origin, creating two replication forks.

Cell Cycle, DNA Replication, and Regulation in Microbial Genetics

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