4. What is the function of 3\' to 5\' exonuclease activity in DNA polymerases? W

Question

4. What is the function of 3' to 5' exonuclease activity in DNA polymerases? What would boe activity in D the consequence of mutating this activity of DNA polymerase III on the fidenty o replication of E. coli DNA? 5. What mechanism does a cell use to repair double-strand breaks in its DNA? How does this differ from the repair of single-strand breaks? 6. Patients with xeroderma pigmentosum suffer an extremely high incidence of skin cancer but have not been found to have correspondingly high incidences of cancers of interna organs (e.g., colon cancer). What might this suggest about the kinds of DNA damage responsible for most internal cancers?

Explanation / Answer

4. 3'to5' exonuclease activity of DNA polymerase helps in proofreading which is a process of removal of incorrect basepairs. When there is an incorrect incorporation of a base pair DNA polymerase will move backwards and by its 3'to 5' exonuclease activity it excises the incorrect basepair. Mutating this acivity will result in incorporation of a number of incorrect basepairs which will result in a number of mutations in the genome.

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