Bio 240 Chapter 15 Notes!
Bio 240 Chapter 15 Notes! Bio 240
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This 0 page Class Notes was uploaded by Izabella Nill Gomez on Wednesday November 25, 2015. The Class Notes belongs to Bio 240 at University of Tennessee - Knoxville taught by Dr. Hughes in Summer 2015. Since its upload, it has received 55 views. For similar materials see General Genetics (Bio 240) in Biology at University of Tennessee - Knoxville.
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Date Created: 11/25/15
Biology 240 Chapter 15 Notes Mutations can occur within somatic cells not transmitted to progeny or germ cells transmitted to progeny Point mutation change in one base pair to another Missense mutation change in one nucleotide of a triplet within a protein coding portion of a gene that could create a different amino acid Nonsense mutation the triplet is change to a stop codon and no protein is produced Silent mutation codon is altered but no change in the amino acid is produced Transition when a purine replaces a purine or a pyrimidine replaces a pyrimidine Transversion when a purinepyrimidine replaces a pyrimidinepurine Frameshift mutation insertion or deletion of one or more nucleotides in a code that causes a shift in the reading frame Loss of function mutation reduceseliminates the function of the gene product Null mutations result in complete loss of function Dominant mutation results in mutant phenotype in a diploid even when the wild type is present Haploinsuf ciency occurs when a single wildtype copy of the gene does not produce enough gene product to bring wild type phenotype Dominant gainof function mutation results in a gene product with enhanced negative or new functions Dominant negative mutations can directly interfere with product function of wildtype allele Mutant nonfunctional gene product binds to wildtype inactivating the gene Visible mutation alters normalwildtype visible phenotype Nutritional mutation loss of ability to synthesize and amino acid or vitamin Biochemical mutations affect the function of proteins that can affect the wellbeing and survival of the affected individual ex sickle cell anemia hemophilia Behavioral mutations can affect the behavior patterns of an organism Drosophila mating behaviorwing beating Regulatory mutations affect regulation of gene expression Spontaneous mutations changes in the nucleotide sequence of genes that appear to occur naturally No speci c agents are associated with the occurrence and are generally assumed to be accidental occur during DNA replication rate extremely low Induced mutations can be the result of naturalarti cial agents ex irradiation UV chemical agents Mutation rate the likelihood that a gene will undergo mutation in a single generation or in forming a single gamete The rate varies between organisms and genes Mutations are random Some DNA sequences appear to be highly susceptible to mutation and are mutation hot spots Variation between organisms may in part re ect the relative ef ciencies of their DNA proofreading and repair systems LuriaDelbruck uctuation test presented direct evidence that mutations take place spontaneously and randomly Carried out on E coli T1 system T1 infected the E coli cells and lysed the infected bacteria After several generations E coli cells were infected Those with resistance survived and reproduced 2 hypotheses were formed to test whether or not mutations were random Adaptive mutations If adaptive every E coli cell grown on the T1 phage would have a constant probability of resistance to mutation A constant number of resistant colonies from plate to plate from experiment to experiment would exist Random mutations If mutations were random they would not be affected by the presenceabsence of the bacteriophage If the mutation occurred early in incubation mutant cells would produce a large culture of resistant cells If late there would be a smaller culture The number of resistant cells would also uctuate Tautomers several forms of misincorperated nucleotides from DNA replication that may lead to mutation Replication slippage can occur anywhere in DNA but is more common in tandem repeat sequences which are hot spots for DNA mutation Tautomeric shifts purines and pyrimidines can exist in tautomeric forms altered chemical forms that differ by 1 proton shift change bonding structure of the molecules allowing noncomplimentary bonding to take place Can lead to permanent basepair changes and mutations Ex TG CA Depurination loss of one of the nitrogenous bases in an intact doublehelical DNA molecule Usually A or G If a glycosidic bond linking 1C and 9 of purine is broken what is left is an apurinic site Deamination Amino group in cytosineadenine is converted to a keto group The cytoplasm is converted to uracil adenine to hypoxanthine Alters base pairing May occur naturally due to treatment with chemical mutagens DNA can also suffer damage from byproducts of normal cellular processes such as ROS reactive oxidative species generated during normal aerobic respiration Can create a loss of bases modi cation and singlestranded breaks Transposons DNA elements that can move within or between genomes Present in all genomes and comprises large portions of it can act as naturally occurring mutagens Can alter the reading frame or introduce stop codons in coding region in regulator regions can disrupt proper expression can also cause chromosomal damage Mutagens have the potential to damage DNA and cause induced mutations 9ex UV fungal toxins Xrays Base analogs compounds that can substitute for purines or pyrimidines during nucleic acid bio synthesis Ex 5BU can turn into BrdU and replace thymine causing a tautomeric shift increasing sensitivity to UV 2AP can be the analog to adenine CH3 CH3CH Alkylating agents donate alkyl groups 2 to amino or keto groups Transition mutations can result lntercalatind adents chemical agents that have dimensions and shapes that allow them to wedge between base pairs of DNA Can cause base pairs to distort and DNA strands affecting transcription replication and repair Can be used as DNA stains or for chemotherapy Adductformind adents substances that bind to DNA altering and interfering with replicationrepair Ex HCA from cigarettes Electromagnetic spectrum full range of wavelength Energy varies with wavelengths UV is the most intense at 260 nm Can create pyrimidine dimers chemical species consisting of 2 identical pyrimidines with 2 thymine residue lnhibit normal replication Ionizing radiation results from Xrays gamma and cosmic rays more energetic than UV Stable molecules turn into free radicalschemica species containing one or more impaired electrons Can affect genertic material by disrupting integrity of chromosomes and producing chromosomal aberrations deletions translocations chromosomal segmentation DNA repair is essential to maintaining genetic integrity Mismatch repair can be activated to remedy basebase mismatches The correct nucleotide is inserted Unmethylated DNA is checked for mismatch endonuclease enzyme nicks the backbone exonuclease unwinds and degrades the nick until the mismatch is reached Then DNA polymerase lls the gap and the correct DNA strand is used Postreplication repair occurs after damaged DNA is not repair Unreplicated gap in lesion of DNA is corrected by Rec A using an undamaged potion of the parental strand that is complimentary and recombined The new gap is then lled by DNA Pol and DNA ligase homologous recombination repair SOS repair system also responds to damaged DNA that allows replication to occur even in damaged DNA better than no replication Photoreactivation enzyme PRE helps reverse UV induced damage if cells are brie y exposes to blue range in visible spectrum Cleaves bonds between thymine dimers photoreactivation repair is no absolutely essential in E coli Humans lack photoreactivation repair Excision repair is used as another system of repair 1 The error is clipped out by endonuclease 2 DNA Pol lls the gap through complimentary replication template 3 DNA ligase seals the gap 2 tvpes of excision repair Base excision repair corrects damaged DNA base Recognition by DNA gycosylase of which a number recognize speci c bases Glycosidic bond between base and sugar coating apyrimidicapurinic site AP endonuclease recognizes the missing base and cuts the phosphodiester backbone Endonuclease removes the sugar the gap is lled by DNA Poland seals by ligase ln nucleotide excision repair bulking lesions in DNA that alter the double helix are xed includes UV UVr gene products clip out lesions along with a few nucleotides on either side Repair is computed by DNA Pol land ligase Xeroderma pigmentosum genetic recessive disorder with severe skin abnormalities cancers neurological effects etc 2000fold higher rate of cancer Defect in nucleotide excision repair pathways Cells from XP are de cient in DNA synthesis other than chromosome replication unscheduled DNA synthesis Done by UV radiation Discovered by somatic cell hybridization Fibroblast fusion of cells in XP heterokaryotes formed Common cytoplasm 2 different nuclei If no NER 1 gene is affected lf occurs complimentation allows 1 normal copy of NER 7 different genes are involved in NER for humans 5 for NER 1 with de cient photoreactivation repair 2 post replication repair de ciency Cockayne syndrome is associated with developmentalneurological defects and sensitivity to sunlight but not increase in cancersvictims age prematurely Trichothicoystrophydwar sm retardation brittle hair facial deformities Sensitive to sunlight but no cancerslife span is about 6 yearsarise from genes encoding NER Double strand break repair DSB repairresponsibe for reattaching 2 broken DNA strands Homologous recombination repair the enzyme recognizes the break digests the 539 end of the broken DNA to leave overhanging 339 ends One overhanging end searches for a region of sequence complimentary on the sister chromatid and aligns then DNA synthesis proceeds from 339 overhanging ends using undamaged DNA strands as templates Occurs in late S or early 62 after DNA replication Nonhomologous end joining activated in 61 before DNA replication can use protein kinase DNA dependent and BRCA1 Others bind to free ends of broken DNA form end and ligate together Errorprone repair system some nucleotides may be lost If more than 1 chromosome suffers a double break wrong ends could be formed Ames test uses strains of salmonella to reveal mutations in food pesticides water etc His is tested for reversion mutations within the mutant gene yielding wild type bacteria Increased sensitivity to mutagens due to no excision repair and bacterial coat Carcinogens are identi ed through the Ames test and shown to be strong mutagens Possible Exam questions 1 Genetic elements that can move around the cell are called a transposons b Insertion sequences c Activator Dissociator d Copia e All of the Above 2 When treating an organism with a mutagen although it is possible that homozygous mutations will occur it is more likely that most new mutations will be heterozygous or hemizygous True 3 Which of the following name two mutagens that would be classi ed as base analogs answer 5bromuracil and 2amino purine