BIOL 200 Lecture Notes - Lecture 6: Dna Glycosylase, Dna Ligase, Helicase
Document Summary
In leading strand, dna replicated by dna pol . Mutations: permanent, transmissible (can propagate to every single cell). Mutagens: chemicals/radiation that mutation frequency. (e. g. uv, x-rays (an example of ionizing radiation) In eukaryotes, dna and have 3" to 5" exonuclease or. Exonuclease: enzymes; cleave nucleotides one at a time from the end (exo) of a polynucleotide chain o. Cytosine undergoes deamination, forming uracil (spontaneous; c-nh2 becomes c=o) When cytosine is methylated, becomes 5-methyl cytosine, then deaminates to become thymine o. Dna glycosylase comes in, takes out the thymine that"s incorrect (mispaired) by hydrolyzing the bond b/w t and sugar-phosphate backbone. Then, ape1 (apurinic/apyrimidinic endonuclease 1) cuts the dna backbone. Ap lyase (part of dna pol ) removes deoxyribose phosphate. Msh2, msh6 bind to daughter strand, triggering binding and activity of mlh1 endonuclease (dimerized w/ pms2) Dna helicase unwinds and dna exonuclease digests segment of daughter strand. Gap repair by pol and dna ligase.
