A tumour starts from one cell. Its cells double in number every 2 days, and none is lost…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A tumour starts from one cell. Its cells double in number every days, and none is lost. Use one billion, , as a round figure for a large tumour.
- How many whole doublings does it take to reach at least one billion cells?
- How many days is that?
- How many cells are there after doublings?
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.
Given. Doubling time: days. Target: cells.
Plan. Find the number of doublings with .
Step 1. Doublings. is below a billion, and is above it. So doublings.
Step 2. Time. days.
Step 3. After doublings. cells, about a million.
Answer: doublings; days; cells.
Check. doublings give only a million cells. Ten more doublings multiply that by .
Watch out. The tumour has a million cells after days, and a billion after days. The last doublings make most of the cells.
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