Question

5

J. D e Cincaumg Vs Tassu15 JUD. 4. Describe proofreading mechanisms carried out by DNA polymerase 5. Identify different steps that give rise to high-fidelity DNA synthesis

Answer 1

Answer 1. DNA polymerases are the enzymes that build DNA in cells. During DNA replication, most DNA polymerases can “check their work” with each base that they add. This process is called proofreading.

Answer 2.

Mismatch repair-

Mismatch repair happens right after new DNA has been made, and its job is to remove and replace mis-paired bases the one not fixed during proofreading. Mismatch repair can also detect and correct small insertions and deletions that happen when the polymerases "slips," losing its footing on the template.

Steps –

A protein complex recognizes and binds to the miss-paired base. A second complex cuts the DNA near the mismatch, and more enzymes chop out the incorrect nucleotide and a surrounding patch of DNA. A DNA polymerase then replaces the missing section with correct nucleotides, and an enzyme called a DNA ligase seals the gap.

Damage repair- Repair processes that help fix damaged DNA include-

Double-stranded break repair in which two major pathways, non-homologous end joining and homologous recombination, are used to repair double-stranded breaks in DNA

Excision repair in which damage to one or a few bases of DNA is often fixed by removal and replacement of the damaged region. In base excision repair, just the damaged base is removed. In nucleotide excision repair, as in the mismatch repair a patch of nucleotides is removed.

Direct reversal in which some DNA-damaging chemical reactions can be directly "undone" by enzymes in the cell.