GEN 3022 1st Edition Lecture 28 Outline of Last Lecture I Nature of mutations a Different theories of mutation patterns b Spontaneous mutations c Induced mutations II Mutation rates and frequencies a Mutation rate b Mutation frequency c Ames test III DNA repair a General process b Base Excision Repair BER c Nucleotide Excision Repair NER d Mismatch repair systems i DNA polymerases ii Important traits iii Mechanism e Recombination i DNA double strand breaks These 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 ii Chromosomal rearrangements iii DNA double strand break repair Outline of Current Lecture I Nature of mutations a Characteristics of mutations b Gene expression II Types of mutations a Missense mutations b Germ line mutation c Conditional mutation d Position effect e Silent mutation f Neutral mutation g Frameshift mutation h Nonsense mutation III Mutation rate a Ames test IV DNA repair a DNA polymerase b Non homologous end joining c Removal of segment of DNA d Base excision repair e DNA mismatch repair Current Lecture I Nature of mutations a Characteristics of mutations permanent changes to DNA sequence produce allelic variation and are more likely to be harmful than beneficial b Gene expression there are many types of mutations that can occur outside of the coding region and affect gene expression These include promoter sequence regulatory sequence 5 UTR 3 UTR and splice recognition sequence II Types of mutations a Missense mutation when a codon is changed so that it encodes a different amino acid than the wild type b Germ line mutation a type of mutation that occurs in gametes and is passed down to progeny c Conditional mutation a mutation that occurs only in a certain set of environmental conditions ex temperature sensitive mutation Siamese cats d Position effect a change in gene expression that results from a breakpoint occurring in a chromosome and rearrangement of the genes Gene expression is suppressed if the gene is moved next to a regulatory sequence or into a heterochromatic region e Silent mutation mutations that do not alter the amino acid sequence even though the nucleotide sequence has changed f Neutral mutation a missense mutation that has no detectable effect on protein function g Frameshift mutation addition or deletion of a number of nucleotides not divisible by 3 in the coding region of a gene Insertions of 3 base pairs or multiples of 3 base pairs do not have a dramatic effect on protein function h Nonsense mutation change from a normal codon to a stop codon III Mutation rate the likelihood that a specific gene will experience a new mutation a Ames test the goal of this test is to determine if a compound is a mutagen This is done by using a strain of bacteria with a mutation in the histidine gene responsible for synthesizing histidine This bacteria is combined with the potential mutagen and another bacteria that grows in the presence of histidine If the mutagen is capable of reversing the first mutation then there will be a large growth of bacteria on the plate A control plate is also made without the mutagen to compare the mutation rate that occurs without the outside factor IV DNA repair a DNA polymerase first method of proofreading DNA Reads in the 3 to 5 direction b Non homologous end joining repairs double strand breaks in DNA by joining the two ends of the DNA together using proteins This type of repair frequently results in deletions c Removal of segment of DNA occurs in almost all DNA repair mechanisms including non homologous end joining base excision repair mismatch repair and nucleotide excision repair d Base excision repair involves removing an abnormal base from the DNA and excising the segment in that region e DNA mismatch repair a type of DNA repair which requires the repair molecules to distinguish between the DNA template and the daughter strand This is an important feature because the repair machinery needs to correct the right base and if it can t discern the difference between the two strands it may not repair the right one If the repair system did not repair the correct strand the progeny would carry the mutation as well The distinguishing feature between the two strands is that the daughter strand is not methylated and the template strand is
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