DNA Mutation and Repair

• base substitutions
• deletions
• insertions

• transition: purine is substituted with another purine or pyrimidine substituted with another pyrimidine
• transversion: when a purine substituted for a pyrimidine or pyrimidine replaces purine

where there is a base change on the third position of the codon but there is no change in amino acid

• when a base substitution that results in a different amino acid and leads to a different polypeptide sequence. The change in polypeptide is either conservative or nonconservative
• conservative: when the changed polypeptide is similar and has little effect on the function/structure of protein
• nonconservative: when the changed polypeptide leads to a very bad resultant protein structure (ex. sickle cells)

when a base substitution leads to a stop codon ultimately ending translation and results to a nonfunctional protein

a deletion of a base resulting in frameshift.

• errors in DNA replication
• errors in DNA recombination
• chemical damage to DNA
• radiation

• mismatch repair
• nucleotide excision repair (NER)
• direct repair of damaged DNA
• recombination repair

when MutS recognizes and binds to the mismatched base pair. MutU unwinds the DNa strand in the direction of the mismatch and exonuclease degrades the strand. DNA polymerase then fills in the gap and ligase seals the nick

formation of a complex of proteins XPA, XPF, ERCC1, HSSB where the transcription factor TFIIH binds to the complex and makes an incision.

specialized enzyme directly repair DNA without having to excise the nucleotide

a mechanism that allows a cell to replicate past the damage and fix it later

• p53 is a transcriptional regulatory factor that controls the expression of gene products that affect cell cycling.
• cancer is caused by inactive or absence of p53 gene
• p21 protein binds and inactivates cell division kinase which results in cell cycle arrest.