5. (5 points) Provide a plausible explanation for the biological importance of DNA damage bypass. How is cell survival enhanced by permitting replication forks to continue through sites of unrepaired DNA damage? Please answer using no more than four sentences.
One possible answer (for which I gave full credit):
Replication forks stop when they come to damage in the template strand. If replication forks stop for a long time, the cells containing them die. So damage bypass is essential for cell survival.
A second possible answer (for which I also gave full credit):
In addition, when cells replicate their DNA, they generate sister chromatids, which are essential for repair of double-strand breaks by the error-free process of synthesis-dependent strand annealing. In other words, replication generates sister chromatids, and sister chromatids enhance repair. In the absence of damage bypass, cells wouldn't be able to generate sister chromatids.
When you answered this question, some of you were confused by a tendency to think of damage bypass as a type of damage repair. Let me repeat: damage bypass is just what the name implies. During damage bypass, damaged regions are bypassed by replication forks; the process of damage bypass does not by itself lead to repair of damage.
Some of you thought that damage in non-coding regions is normally bypassed while damage in genes is repaired. So far as I'm aware, that's not correct. Damage bypass takes place with equal efficiency in coding and non-coding regions.
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