Question

My copy of the Molecular Biology of the Cell (the 5th edition, so not entirely up to date) seems to claim that exonuclease action is an important part of DNA proofreading, and that dysfunction in this leads to an increased rate of mutation (pp 276-277).

But at the same time it specifies that exonuclease action is only useful in removing incorrect bases from DNA-primers (p. 270). That means that only the base pairs in the one primer on the leading strand would be proofread, and only a minority of the base pairs in the lagging strand (The primers are vastly more numerous, but still only a minority of base pairs will be found inside primers).

In addition, these primers are made out of RNA and are only temporary, so I can’t see why mutations in these sequences would be considered important. They are replaced with DNA-segments at the end anyway and it’s these final DNA-segments that ought to be proofread.

So how can exonuclease action be considered an important (or even vaguely relevant) proofreading mechanism?

Answer 1

Exonuclease action is an important proofreading mechanism in DNA replication. It helps remove incorrect bases from RNA primers on both the leading and lagging strands. This ensures accurate DNA synthesis and reduces the rate of mutations.

Step-by-step explanation:

Exonuclease action is an important proofreading mechanism in DNA replication. Although primers on the leading and lagging strands are RNA and temporary, errors can still occur when these primers are synthesized. Exonuclease activity helps in removing incorrect bases from the DNA primers, ensuring that only correct bases are added during replication. This improves the accuracy of DNA synthesis and reduces the rate of mutations.