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Question

When cell has stalled DNA replication fork, which checkpoint should be predominantly activated?
  1. G1/S
  2. G2/M
  3. M
  4. Both G2/M and M


Solution

The correct option is B G2/M
In a typical eukaryotic cell, there are stages at which the cell "checks" to decide if it needs to proceed. Among these, are three such checkpoints that are most important - G1, G2 and M checkpoints.
  • The G1 checkpoint, which is at the G1/S transition, checks the DNA for any damaged bases and prevents the copying of the DNA if these bases are not fixed. The checkpoint then allows for proper mechanisms to go through and fix those mutations in the genome. When these damaged bases are fixed the cell can then progress onto the S phase, where the DNA actually replicates.
  • In the G2 checkpoint, which is at the transition between G2/M, DNA is checked for incompletely replicated or damaged DNA.
  • The M checkpoint, also known as the spindle checkpoint, which is at the transition from metaphase to anaphase, checks if the spindle microtubules are properly attached to the sister chromatids at the metaphase plate.
Thus, the correct option here is D, G2/M, which is the G2 checkpoint. This should be activated as the cell has stalled DNA replication fork.

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