How do cells know that there is something wrong with the dna?

The short answer is that cells respond to the chemical environment in which they find themselves. The cells around them, the specific conditions, and feedback from the environment all create specific chemical cues that inform the cells to which genes should be expressed, and in what amounts. Chemicals include hormones, cytokines, general signaling molecules, such as cAMP, etc.

i literally hopped on google for this, lol.
i hope this helps though. :)

What is the example? i’ll be happy to answer if you can tell me : )