University:
The University Of Western Ontario
Course:
Biology 2290F | Scientific Method in Biology
Academic year:

2022
Views:

122

Pages:

3
Author:

Kyuwon J.

Sources of DNA damage ○ ○ exogenous ■ UV ■ chemicals ■ ionizing radiation (gamma, Xrays) endogenous ■ rep. errors ■ mitochondria ROS DNA proofreading During Replication ● DNA polymerase 3 has 3’ => 5’ exonuclease activity ○ Few errors could be made ○ Can be fixed by own proofreading mechanisms ○ 3’ - 5’ exonuclease activity ■ DNA polymerase 3 removes mismatched bases , then insert the correct base in correct orientation Exclusion repair 1. Repair enzymes a. Detects distortion 2. Endonuclease activity-cutting backbone 3. DNA polymerase fills in the gap 4. Ligase seals the nick ● How DNA gets repaired (excision repair, photolyase, Non-homologous end joining) ○ when proofreading fails ○ repair enzymes cut newly synthesized strand (recognize distortion of backbone), nick filled in ○ thymine dimers formed via UV repaired by photolyase + white light ■ humans lack photolyase → have excision repair enzymes ○ non-homologous end joining: sloppy + can result in mutation ● If both proofreading fails mutation will happen ○ Once DNA is replicated ○ Variation increase Thymine Dimers ● Thymine dimers form under UV lights (damage) ● Repairs by photophase and white light ● ● Mammals lack photolyase => excision repair is needed ● How DNA gets repaired (excision repair, photolyase, Non-homologous end joining) ○ when proofreading fails ○ repair enzymes cut newly synthesized strand (recognize distortion of backbone), nick filled in ○ thymine dimers formed via UV repaired by photolyase + white light ■ humans lack photolyase → have excision repair enzymes ○ non-homologous end joining: sloppy + can result in mutation