What proofreading occurs during replication In terms of endo

What proofreading occurs during replication? (In terms of endonuclease and exonuclease activity)

How does this differ between eukarya and bacteria?

Solution

Proof reading refers to 3’ – 5’ exonuclease activity. DNA replication or nucleotide polymerization occurs in 5’ – 3’ direction. Whenever a wrong base or mismatched base is incorporated, polymerase has the ability to remove the incorporated nucleotide by moving in 3’ – 5’ direction (the direction opposite to replication). After inserting correct nucleotide, polymerase again moves in 5’ – 3’ direction.

Proof reading mechanism is similar in both bacteria and eukaryotes. All the three bacterial DNA polymerases have proof reading ability. Whereas, in eukaryotes, only two DNA polymerases (DNA pol delta and DNA pol epsilon) have the proof reading ability. These two are main replicating enzymes in eukaryotes.