How is it that the fidelity of DNA synthesis...

[matt k]

...is caused to be 1 mutation per 10^9 base pairs duplicated.? How does DNA polimerese achieve this fidelity, and why is the fedelity of DNA replication not 100%.

[lindsey1062003]

well, sometimes dna polymerase sees the mutation on the new strand, but instead of changing it to match the old strand, it changes the old strand to match the mutation on the new.
for example, if the nucleotide pairing at one spot should be AT, [A being on the old strand, T on the new] but for some reason gets changed to AC and the polymerase comes by and changes it to GC, then youve got a messup and possibly a deadly mutation.

[Dizz]

DNA polymerase has a proofreading ability and a 3' to 5' exonuclease activity in the event of mismatch.

Since there are roughly 3 x 10^9 base pairs of DNA in the human genome a mutation rate of one per 1 x 10^9 means on average 3 mutations for each replication. Most of these are in noncoding regions though.

Fidelity of DNA replication by virtue of DNA polymerase activity is under tremendous selection pressure. Consider an individual with a mutant form of DNA polymerase who had an error rate 10 times higher. The cells of this individual would be 10 times more likely to have a significant mutation.

Some (very low level) mutation is good in an evolutionary sense. Lots of mutations are detrimental to the overall evolutionary fitness however.