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Unformatted text preview: Sheet1 Page 1 Review Test number 3 Bacterial Genetics h Explain phenotype and genotype. Genotype - The specific set of genes present in a cell or virus Phenotype - Expressed, measurable characteristics. h Describe the effects of point mutations. The most frequent type of mutation and it happens at the - DNA level: change in a single nucleotide base pair -Transition “ pyrimidine for a pyrimidine or a purine for a purine -Transversion & purine for a pyrimidine or vice versa -At the Protein level: Change translates in the amino acid sequence -Silent X No change in amino acid sequence ¶ no phenotypic affect - Neutral - Change to equivalent amino acid - no phenotypic effect -Missense: Changes amino acid sequence: Phenotypic effect ranges from slight to strong depending on sequence. -Nonsense: Introduces stop codon producing truncated protein Phenotypic effect is usually strong. -Frameshift: Changes codon reading frame. Phenotypic effect is Usually strong. h Describe the DNA repair mechanisms that correct mutations. DNA repair of UV damage: -1st mechanism: photo-reactivation repair h UV light (<280 nm) is mutagenic h Causes thymine dimerization h Dimers are repaired by visible lightinduced Photolyase enzyme. -2nd mechanism: Excision Repair h Three step process: 1. Endonucleases remove damaged DNA 2. DNA polymerase I re-synthesizes 2 DNA 3. DNA ligase joins the two fragments -3rd mechanism: Recombination Repair -AKA homologous recombination h Important form of repair/exchange involving homologous genes. h Complex process that requires ~25 proteins/enzymes. h Involves recA protein that is involved in DNA repair. - RecA protein & has been shown to be essential in every Homologous recombination pathway h Non-incorporated DNA is degraded. h Describe the effects of insertion sequences, transposons and plasmids. Insertion sequences “ small mobile DNA (~ 1 kb), short inverted repeats at the ends (~20 kb), encoded transposase Enzyme Transposons: Larger mobile DNA (<40kb), Can carry additional genes Sheet1 Page 2 Example: antibiotic resistance E Widely used tool in microbial genetics. Example: Tn5 mutagenesis) PLASMIDS: h Autonomously replicating genetic elements h Usually double stranded DNA (1-1000 kbp) h Replicate like DNA or by rolling circle h Multiple plasmids per cell can occur h Plasmids encode 2-30 genes that can encode for multiple processes h Antibiotic production h Catabolic processes Example: Oil breakdown h Antibiotic resistance (R plasmids) h Toxin production (pathogenesis) h Grouped by compatibility / incompatibility h Some are conjugative (F plasmid) some are not (cryptic). F Plasmid and conjugation F h Describe horizontal gene transfer: Transformation, Conjugation and Transduction....
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- Spring '08