MMG301 1nd Edition Lecture 22Outline of Last Lecture I. VirusesOutline of Current Lecture II. Mutations in bacteriaIII. Repair mechanismsCurrent Lecture-mutations in bacteria-point mutations: substitutions involving one DNA base pair-silent mutation: there is a change in the DNA sequence, but the new codon codes for the same amino acid (DNA sequence changes, protein sequence does not)-nonsense mutation: results in a stop codon-missense mutation: results in a different amino acid-frameshift mutation: results from an insertion or deletion that changes the triplet reading frame-most mutations are caused by chemicals or radiation that cause chemical changes to DNA bases-radiation-ultraviolet: formation of pyrimidine dimers in DNA (DNA can’t replicate properly)-ionizing radiation: breaks in DNA, chemical damage to DNA bases, damage to other molecules-prokaryotes: have ability to repair many types of DNA damage, have…-enzymes that replace damaged DNA basesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-polymerases that can replicate through damaged regions-E. coli, like most bacteria, have DNA repair systems-SOS system: a regulon of about 40 genes involved in repair of DNA damage and damage tolerance-types of enzyme-catalyzed DNA repair mechanisms-photo-repair (light repair): enzyme uses light energy to replace thymine dimers-excision repair: enzymes remove a single-strand piece of damaged DNA; DNA polymerase fills in the resulting gap-mismatch repair: enzymes remove damaged DNA base; resulting single base gap is filledin by DNA polymerase-SOS regulon control enzymes-RecA: is activated by DNA damage; multifunctional enzyme-LexA: a repressor of many SOS genes; repressor prevents transcription of genes of operons-activated RecA becomes a LexA-specific protease and degrades the LexA repressor protein; DNA repair genes are therefore switched “on”-reversions: point mutations that give restoration of a wild-type phenotype; can occur two ways-same site reversion: base pair mutates back to original genotype-second site reversion: mutation at a different site restores the wild-type phenotype…frameshift-example: a base pair insertion that corrects an altered reading frame caused by a nearby deletion-types of mutations involving larger segments of DNA-insertions: new stretches of DNA are added (often longer than a few base pairs)-translocations: rearrangements of regions of DNA; large segments of DNA move to another location on the genome-inversions: orientation of a segment of DNA is reversed; sometimes, large portions of genomes involved-auxotroph: a mutant with a nutritional requirement for growth-wild-type: a strain of microbe as isolated from nature-induced mutations: result from deliberate manipulation of cells: chemical or UV irradiation-spontaneous mutations: occur naturally without human manipulation-mutagens: substances that cause mutations; often chemical compounds that react with or bindto
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