A student measures cyclin B and CDK1 in one cell, in arbitrary units…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student measures cyclin B and CDK1 in one cell, in arbitrary units. The values are invented to show the pattern.
| Time (h) | 0 | 6 | 12 | 18 | 22 | 23 |
|---|---|---|---|---|---|---|
| Cyclin B | 1 | 2 | 4 | 7 | 10 | 2 |
| CDK1 | 5 | 5 | 5 | 5 | 5 | 5 |
- At what time is the amount of cyclin B the highest?
- Which of the two proteins stays at a steady level?
- At which time is the cyclin B and CDK1 complex most active, and what does the cell do then?
- What does the fall between h and h show?
Need a reminder? The key ideaShow
There are three checkpoints. The G1 checkpoint checks the size of the cell, its food, the growth factors and the DNA damage. The G2 checkpoint checks that the DNA is copied and undamaged. The spindle checkpoint checks that every chromosome is attached to the spindle. A CDK has a steady amount and works only when bound to a cyclin. The amount of a cyclin rises and falls.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Cyclin B is highest at h, at units.
Step 2. (b) CDK1 stays at units. This is what a CDK does.
Step 3. (c) At h. There is most cyclin to bind the CDK, so the complex (MPF) is at its most active. The cell is in mitosis.
Step 4. (d) The cyclin B was broken down. The CDK is switched off, and the cell leaves mitosis.
Answer: (a) h; (b) CDK1; (c) h, in mitosis; (d) the breakdown of cyclin B.
Watch out. The numbers are invented. The pattern is real: the CDK is steady and the cyclin rises and falls.
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