Question

At G2/M checkpoint the cell cycle will arrest if

• A. The cell has not achieved an adequate size
• B. The spindle fibre formation has not occurred
• C. The DNA replication or repair of DNA damage has not been completed
• D. The attachment of the spindle fibres to the kinetochore of centromeres is not adequate

Hint:

The G2/M checkpoint ensures that the cell does not proceed to mitosis with damaged or incompletely replicated DNA. Always link this checkpoint with DNA integrity and completion.

Answer 1

The Correct Option is C

Step 1: Understand the cell cycle checkpoints.
The cell cycle is regulated by specific checkpoints to ensure that critical processes such as DNA replication and mitotic spindle formation are completed correctly before the cell proceeds to the next phase. The major checkpoints include:
G1 checkpoint (restriction point)
G2/M checkpoint
Metaphase (spindle) checkpoint
Step 2: Role of the G2/M checkpoint.
The G2/M checkpoint occurs just before the cell enters mitosis (M phase) from the G2 phase. It ensures:
DNA replication is fully completed.
There is no DNA damage.
Any damage that occurred during S or G2 phase is repaired before mitosis begins.
Step 3: Analyze the options.
Option (1): This is more relevant to the G1 checkpoint, which checks for cell size, nutrients, and growth factors.
Option (2): Spindle fibre formation is monitored during the spindle checkpoint (Metaphase checkpoint).
Option (3): Correct — Incomplete DNA replication or unrepaired DNA damage triggers arrest at the G2/M checkpoint.
Option (4): Attachment of spindle fibres to kinetochores is checked during metaphase, not at the G2/M checkpoint.