Name the checkpoint that stops the cycle in each case…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Name the checkpoint that stops the cycle in each case.
- A cell is too small and has no growth factors around it.
- A cell in G1 has ultraviolet damage in its DNA.
- A cell in G2 has copied only part of its DNA.
- A cell in metaphase has one chromosome that is not attached to the spindle.
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) The G1 checkpoint. It checks the size of the cell and the growth factors.
Step 2. (b) The G1 checkpoint. It checks the DNA for damage, and p53 holds the cell for repair.
Step 3. (c) The G2 checkpoint. It checks that all the DNA is copied.
Step 4. (d) The spindle checkpoint. Anaphase waits until every chromosome is attached.
Answer: (a) G1; (b) G1; (c) G2; (d) spindle checkpoint.
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