Question 1

Which of the following best describes the role of cell cycle checkpoints during the G1-S transition?

Accepted Answer

They sense defects and check for sufficient growth and DNA damage repair before allowing the cell to proceed.

Question 2

A mutation in the Rb gene is most likely to result in which of the following cellular outcomes?

Accepted Answer

Uncontrolled cell cycle progression due to loss of E2F inhibition.

Question 3

Which protein is stabilized in response to DNA damage and can lead to cell cycle arrest or apoptosis?

Accepted Answer

p53

Question 4

In the context of DNA replication origins, which statement is TRUE regarding bacterial and eukaryotic replication?

Accepted Answer

Bacterial origins (oriC) are rich in AT sequences and require full methylation for initiation.

Question 5

Which of the following is a function of tumor suppressor genes such as Rb and p53?

Accepted Answer

They inhibit cell cycle progression to maintain cell integrity.

Question 6

A patient inherits one mutated allele of the Rb gene. What is the most likely consequence?

Accepted Answer

They will develop retinoblastoma only if the second allele is also mutated.

Question 7

Which of the following events occurs FIRST during the initiation of DNA replication at the bacterial oriC?

Accepted Answer

Binding of DnaA-ATP to DnaA boxes.

Question 8

What is the consequence of a cell attempting to replicate DNA with unrepaired damage at the G1-S checkpoint?

Accepted Answer

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

Question 9

Which of the following is required for DnaA to initiate replication at the bacterial origin of replication?

Accepted Answer

The origin must be fully methylated on both DNA strands.

Question 10

In eukaryotic DNA replication, what is the role of the Origin Recognition Complex (ORC)?

Accepted Answer

It binds to ARS sequences to recruit licensing factors for replication initiation.

Question 11

Which of the following best explains why eukaryotic chromosomes have multiple origins of replication?

Accepted Answer

To ensure that DNA replication can be completed efficiently within the limited time of S phase.

Question 12

Which checkpoint gene is most commonly mutated in human cancers, often in conjunction with another checkpoint gene?

Accepted Answer

Rb

Question 13

What is the function of p21 and p27 in the cell cycle following DNA damage?

Accepted Answer

They act as inhibitor proteins to block CDK activity and arrest the cell cycle.

Question 14

Which of the following is TRUE regarding the licensing and firing of replication origins in eukaryotes?

Accepted Answer

Licensing factors recruit helicase to origins, forming the pre-replication complex, which is then activated by initiating factors.

Question 15

Which of the following best describes the difference between cis-acting and trans-acting elements in DNA replication?

Accepted Answer

Cis-acting elements are DNA sequences that regulate nearby DNA, while trans-acting elements are proteins that act on these sequences.

Question 16

A researcher observes that a eukaryotic cell has a defect in the ARS consensus sequence. What is the most likely outcome?

Accepted Answer

Replication initiation will be impaired, leading to incomplete DNA replication.

Question 17

Which of the following equations correctly represents the conservative model of DNA replication?

Accepted Answer

$$\mathrm{Parent\ DNA} \rightarrow \mathrm{Parent\ DNA} + \mathrm{New\ DNA}$$

Question 18

If a cell has a constitutively active Ras protein due to a mutation, what is the most likely effect?

Accepted Answer

The cell will undergo uncontrolled proliferation, increasing cancer risk.

Question 19

Which of the following is a multi-step process that occurs during bacterial DNA replication initiation?

Accepted Answer

DnaA-ATP binds to DnaA boxes, melting AT-rich DNA, followed by helicase recruitment and DNA polymerase assembly.

Question 20

Which checkpoint is responsible for ensuring that all chromosomes are properly attached to the spindle before anaphase?

Accepted Answer

Metaphase checkpoint

Cell Cycle Checkpoints and DNA Replication Initiation

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