Cell cycle must be controlled to ensure stages occur in order and continue only when the previous stage is successfully completed.
Cell cycle checkpoints delay the cycle until certain conditions are met.
G1 checkpoint: Cell committed to divide; can enter G0 if not passed; checks for proper growth signals and DNA integrity (apoptosis if repair impossible).
G2 checkpoint: Verifies DNA replication and repair of any DNA damage.
Mitotic stage checkpoint: Ensures all chromosomes are attached to the spindle between metaphase and anaphase.
Cell Cycle Signals
Signals (molecules) stimulate or inhibit cell events.