Question

Difference between 3 prime to 5 prime exonuclease activity

Answer 1

3'-5' is a characteristic feature of DNA-polymerase I. This activity is meant to repair any misparing mistakes that the enzyme may commit during the synthesis, in which the enzyme would reverse its direction by ONE NUCLEOTIDE and excised the mistakenly added nucleotide, the enzyme acts at the phosphodiester bond at the 5 prime.
Whereas the 5'-3' exonuclease activity is an also repair strategy exercised by the DNA polymerase I. However, in this case the polymerase would move in the forwards direction and excise the miss-matched nucleotides at any position regardless with one nucleotide far or so many. This mechanism of repair is well documented in case UV-mutation.