Which checkpoint is designated to verify proper attachment of sister chromatids to the mitotic spindle, typically considered the final checkpoint before cell division proceeds?

Which checkpoint is designated to verify proper attachment of sister chromatids to the mitotic spindle, typically considered the final checkpoint before cell division proceeds?

• A. G1 checkpoint
• B. G2 checkpoint
• C. S-phase checkpoint
• D. M checkpoint

Answer: (D)

The spindle assembly checkpoint during mitosis ensures sister chromatids are properly attached to the spindle via kinetochores and that they are under the correct tension before the cell proceeds to anaphase. This final surveillance gate checks that all chromosomes are bi-oriented on the metaphase plate; only when this condition is met does the cell activate the anaphase-promoting complex to trigger cohesin cleavage and sister chromatid separation. If attachments aren’t correct, the checkpoint halts progression to allow corrections, preventing mis-segregation. Earlier checkpoints exist that monitor other aspects of the cycle—before a cell enters DNA replication, the system checks for adequate growth signals and DNA integrity, and during S phase it monitors ongoing DNA synthesis. These do not directly verify spindle attachment, so the checkpoint described here is the one that specifically guards proper chromosome-spindle attachments at the end of mitosis.

The spindle assembly checkpoint during mitosis ensures sister chromatids are properly attached to the spindle via kinetochores and that they are under the correct tension before the cell proceeds to anaphase. This final surveillance gate checks that all chromosomes are bi-oriented on the metaphase plate; only when this condition is met does the cell activate the anaphase-promoting complex to trigger cohesin cleavage and sister chromatid separation. If attachments aren’t correct, the checkpoint halts progression to allow corrections, preventing mis-segregation.

Earlier checkpoints exist that monitor other aspects of the cycle—before a cell enters DNA replication, the system checks for adequate growth signals and DNA integrity, and during S phase it monitors ongoing DNA synthesis. These do not directly verify spindle attachment, so the checkpoint described here is the one that specifically guards proper chromosome-spindle attachments at the end of mitosis.