DNA Repair

DNA glycosylase

DNA glycosylase

________ removes the damaged base.

Correct nucleotide

________ is incorporated by DNA polymerase β.

Nucleotide excision repair

________ proceeds most rapidly on the DNA strand that is serving as the template for transcription.

Excision repair

________: damaged base or bases are removed and then replaced with the correct ones.

Excision repair

damaged base or bases are removed and then replaced with the correct ones

Types of excision repairs

Base Excision Repair

Nucleotides Excision Repair

Mismatch Repair

Base excision repair

DNA glycosylase removes the damaged base

Removal of its deoxyribose phosphate

Correct nucleotide is incorporated by DNA polymerase β

Ligation

Nucleotide excision repair

The damage is recognized by one or more protein factors that assemble at the location.

The DNA is unwound producing a "bubble".

Cuts are made on both the 3’ side and the 5’ side of the damaged area and the tract containing the damage can be removed

Using the opposite strand as a template DNA Pol α or ε fills in the correct nucleotides

This is followed by Ligation

Mismatch repair

Mismatch repair deals with correcting mismatches of the normal bases

Follows behind replication fork

Recognition of mismatch require protein complex

Excision of mismatch

DNA synthesis by Pol 𝛼 or 𝜀

Single strand breaks

uses the same enzyme systems that are used in base excision repair

Double-strand breaks

Nonhomologous End Joining = Direct joining of the broken ends

Nonhomologous Recombination