Question

How is the wrong base removed before proceeding to add new bases in the 5’ - 3’ direction during DNA replication?

Answer 1

The removal of an incorrect base during DNA replication is performed by the DNA polymerase enzyme through a process called proofreading.

When the enzyme detects a mismatched base pair, it immediately pauses and uses its 3’ to 5’ exonuclease activity to move backwards and snip out the incorrectly paired nucleotide from the growing strand. Once the “wrong” base is removed and the 3’-OH end of the strand is correctly aligned again, the polymerase switches back to its 5’ to 3’ polymerase activity to insert the correct nucleotide and resume synthesis.