DNA Mutations

What are the two types of mutations and examples of them?

Induced mutations: Mutagens modify DNA or interfere with replication

• Chemical: Base analogs, DNA modifiers, intercalating agents

• Physical: Radiation

Spontaneous Mutations: Replication errors due to tautomerizations

• Transitions (Purine to Purine or Pyrimidine to Pyrimidine)

• Transversions: Purine to Pyrimidine or vice versa

• Spontaneous DNA lesions

• Mobile genetic elements

Proofreading

• If incorrect nucleotide is detected, DNA Pol III uses 3’→ 5’ Exonuclease activity to remove it

Mismatch repair

• Mut complex can detect and remove bases and mismatches

• Cuts unmethylated strand

• DNA polymerase and ligase fill in removed section

Nucleotide excision repair

• Uvr complex can detect and remove distortions of the double helix (ex. thymine dimers)

• DNA polymerase I and ligase fill in removed section

Direct repair: Photoactivation

• Visible (blue light) activated photolyase which repairs thymine dimers

Base excision repair

• DNA glycosylases remove damaged bases

• DNA polymerase I and ligase fill in the removed section

Recombinational repair

• RecA can cut recently copied DNA to dill a gap or repair DNA on both strands

• RecA also plays a part in the SOS response (complex network that is used a a global response to DNA damage