Drug X stops the copying of DNA. Drug Y stops the spindle from forming…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Drug X stops the copying of DNA. Drug Y stops the spindle from forming. Both are used in chemotherapy.
- In which phase of the cycle is a cell harmed by drug X? And by drug Y?
- A patient on these drugs loses hair, feels sick and gets infections. Explain, using the cell cycle.
- Why are the drugs given in courses with rests between them?
Need a reminder? The key ideaShow
Cancer cells ignore the checkpoints. A proto-oncogene codes for an accelerator of the cycle, and a mutation can turn it into an oncogene (a gain of function). A tumour suppressor gene such as that for Rb or p53 codes for a brake, and a mutation can cut it (a loss of function). A tumour that doubles its cells every days needs doublings to reach cells.
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) Drug X harms cells in S phase. Drug Y harms cells in M phase, at prophase and metaphase.
Step 2. (b) The drugs harm any cell that is dividing. Healthy tissues with fast division are the hair follicles, the lining of the gut and the bone marrow. Damage to the hair follicles gives hair loss. Damage to the gut lining gives sickness. Damage to the bone marrow gives fewer white cells, so the patient gets infections.
Step 3. (c) The rest lets the healthy tissues recover by dividing again. A course catches the tumour cells as they pass through the sensitive phase, because they are not all in the same phase at one time.
Answer: (a) S phase; M phase; (b) fast dividing healthy cells are hurt; (c) the healthy tissues recover between courses.
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