Biology / Unit 4 Bio 0889 short lesson, about 20 seconds
Negative Regulation: Rb, p53, and p21
Captions available
The idea
Retinoblastoma protein, p53, and p21 are the cell cycle's best-understood negative regulators, acting mainly at the G1 checkpoint to block progression until conditions are satisfied.
In practice
Retinoblastoma protein binds transcription factor E2F, blocking the genes a cell needs to enter S phase.
Where people slip
A negative regulator's activity halts the cycle — losing it, not gaining it, allows uncontrolled division.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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