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TORTORA FUNKE CASE ninth edition MICROBIOLOGY an introduction 8 Part B Microbial Genetics Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Translation mRNA is translated in codons (three nucleotides) Translation of mRNA begins at the start codon: AUG Translation ends at a stop codon: UAA, UAG, UGA PLAY Animation: Translation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.2 Translation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.8 Translation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.10 Regulation of Bacterial Gene Expression Constitutive enzymes are expressed at a fixed rate. Other enzymes are expressed only as needed. Repressible enzymes Inducible enzymes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Operon PLAY Animation: Operons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.12, step 1 Regulation of Gene Expression Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.13 Mutation A change in the genetic material Mutations may be neutral, beneficial, or harmful. Mutagen: Agent that causes mutations Spontaneous mutations: Occur in the absence of a mutagen Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mutation Base substitution (point Change in one base mutation) Missense mutation Result in change in amino acid Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.16a–b Mutation Nonsense mutation Results in a nonsense codon Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.16a, c Mutation Frameshift mutation Insertion or deletion of one or more nucleotide pairs Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.16a, d Mutation Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone. Nucleotide excision repairs mutations. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mutation UV radiation causes thymine dimers. Light-repair separates thymine dimers. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.19 The Frequency of Mutation Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes Mutagens increase to 10–5 or 10–3 per replicated gene. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Selection Positive (direct) selection detects mutant cells because they grow or appear different. Negative (indirect) selection detects mutant cells because they do not grow. PLAY Animation: Mutations and DNA Repair Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Genetic Transfer and Recombination Vertical gene transfer: Occurs during reproduction between generations of cells. Horizontal gene transfer: The transfer of genes between cells of the same generation. PLAY Animation: Horizontal Gene Transfer Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Transformation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.23 Recombination Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.24 Conjugation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.26a Conjugation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.26b Conjugation PLAY Animation: Bacterial Conjugation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.26c Transduction Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.27 Plasmids Conjugative plasmid: Carries genes for sex pili and transfer of the plasmid Dissimilation plasmids: Encode enzymes for catabolism of unusual compounds R factors: Encode antibiotic resistance Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Plasmids Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8.28 Sensitive to DNase? a. b. c. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings You have isolated a strain of E. coli that is resistant to penicillin, streptomycin, chloramphenicol, and tetracycline. You also observe that when you mix this strain with cells of E. coli that are sensitive to the four antibiotics, they become resistant to streptomycin, penicillin and chloramphenicol, but remain sensitive to tetracycline. Explain what is going on. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings