Cell checkpoints

Question

What are the similarities and differences between the G2 and the M phase checkpoints? What are the phenotypic outcomes for the cell when either of the two checkpoints fails but the cell continues to divide?

Answer 1

Both checkpoints stop the cell from dividing with mistakes, but G2 checks DNA damage and M checks chromosome alignment.

Both pause the cell cycle via Cdk regulation, but they check different things.G2 checkpoint (end of G2): Checks if DNA replication is complete and if DNA is damaged. Regulated by ATM/ATR -> p53/p21 -> inhibits Cdk1/Cyclin B. If it fails and the cell divides, daughter cells inherit broken chromosomes with deletions/translocations leading to mutation or apoptosis.M checkpoint [Spindle Assembly Checkpoint, metaphase]: Checks if all chromosomes are attached to spindle microtubules with tension at kinetochores. Regulated by Mad2/Bub proteins that inhibit APC/C. If it fails, nondisjunction occurs leading to aneuploidy [wrong chromosome number] like monosomy/trisomy.In both cases, failure can lead to aneuploidy, genomic instability, and is a hallmark of cancer.I teach this with custom diagrams of Cdk1/Cyclin B and the kinetochore - happy to walk through it step-by-step in a session if you want the full pathway.