The Cell That Times Itself

You'll learnhow the rise and fall of one protein times the cell cycle, and what the checkpoints do to it.

There is no clock inside a cell. There is one protein that gets built up and then torn down, over and over, and the rise and fall of that single concentration is what times every step of the cycle. Around it sit three gates, and at each one the cell stops and asks itself a question it is allowed to answer no to. Eleven short steps; press Next for each one.

AP BIOLOGY · 11 STEPS · 6 QUICK CHECKS · CYCLIN RISES AND FALLS · CDK IS OFF WITHOUT IT · CANCER = LOST CONTROL, NOT SPEED · v5

one protein builds up · three gates ask · the engine is held

Before you start

What you're looking at

A graph of one protein’s concentration across a turn of the cell cycle, rising to a peak just before mitosis and then collapsing.

The question

What advances the cell cycle when there is no actual clock inside the cell?

Step 1 / 11