BIO 3170 Lecture Notes - Lecture 4: Pyrimidine Dimer, Depurination, Pyrimidine
11 Apr 2018
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Document Summary
Dna is under constant threat of damage: during replication, reactive metabolites (especially in mitochondria - exposed to a lot of oxidation), environmental agents. Exogenous: external sources, can cause strand damage and breaks. Alkylating agents: add methyl groups to bases and interstrand cross links. Uv light: interstrand and intrastrand pyrimidine dimers. Damage on one strand: repair pathways relying on double-stranded structure - relies on intact strand: eliminate the damaged portion and use the intact strand as a template to replace the nucleotide. Damage on both strands: no intact strand to serve as template for repair: use recombination from homologous chromosome/other chromatid. Types of dna damage: nucleotide, helical structure, dna strand break. Two-base alterations: covalent bonds are introduced between two consecutive nucleotides on the same strand, forming dimers. Chain breaks: breaking phosphodiester bond - doesn"t alter or damage the bases. Cross-linkage: the two chains are cross-linked, preventing the dna helix from being undone. Dna binding proteins can also be cross-linked.
