Cell Cycle Question
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 Garter
 Posts: 3
 Joined: Wed Nov 07, 2012 2:05 am
Cell Cycle Question
Hi,
I'm studying this practice test and it has this question about radioactive thymidine exposure during the cell cycle.
I understand that it takes 1 hour for Radioactive thymidine to be first detected due to the length of G2, which, paired with S phase, is when DNA replication occurs. Therefore, at 2 hours, the first set of cells would have just finished Mphase and the next set of G2 cells would have entered Mitosis. However, I'm not entirely sure how to caculate that 20% of labelled cells are in M phase at 2 hours after thymidine exposure.
any help would GREATTTTTLY be appreciated. I attached the question in a jpg to this post.
I'm studying this practice test and it has this question about radioactive thymidine exposure during the cell cycle.
I understand that it takes 1 hour for Radioactive thymidine to be first detected due to the length of G2, which, paired with S phase, is when DNA replication occurs. Therefore, at 2 hours, the first set of cells would have just finished Mphase and the next set of G2 cells would have entered Mitosis. However, I'm not entirely sure how to caculate that 20% of labelled cells are in M phase at 2 hours after thymidine exposure.
any help would GREATTTTTLY be appreciated. I attached the question in a jpg to this post.

 Garter
 Posts: 3
 Joined: Wed Nov 07, 2012 2:05 am
Re: Cell Cycle Question
Sorry, I think I figured it out.
It's not so much a cellular bio question, just tricky.
In case anyone's wondering, this is what I think it is. It's that all the cells T = 1 hour have either entered G2 phase or are somewhere in S phase (That's the only way that 100% of the cells can be radioactively labelled at 2 hours). Assuming equal distribution of cells across S phase (i.e. 20% in 1st hour, 20% in 2nd hour, etc...) 20% of cells would be entering G2 phase at T=1hr. Those 20% of cells would then enter Mphase at T=2hr.
Am I right in this assumption?
It's not so much a cellular bio question, just tricky.
In case anyone's wondering, this is what I think it is. It's that all the cells T = 1 hour have either entered G2 phase or are somewhere in S phase (That's the only way that 100% of the cells can be radioactively labelled at 2 hours). Assuming equal distribution of cells across S phase (i.e. 20% in 1st hour, 20% in 2nd hour, etc...) 20% of cells would be entering G2 phase at T=1hr. Those 20% of cells would then enter Mphase at T=2hr.
Am I right in this assumption?
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