Cell cycle checkpoints
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
G1/S restriction point (checks DNA damage, cell size); G2/M (DNA replication complete); spindle assembly checkpoint (chromosome attachment).
Cell cycle checkpoints in plain English
Checkpoints are the cell's quality-control inspectors that pause division to make sure everything is safe before moving on. At the G1/S checkpoint the cell asks "Am I big enough, and is my DNA undamaged?" before it starts copying its DNA. At the G2/M checkpoint it double-checks that the DNA was fully and correctly copied before splitting. Finally, the spindle assembly checkpoint makes sure every chromosome is properly hooked to the ropes that will pull it apart — like a pilot running a pre-flight safety list, refusing to take off until each item passes.
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