Copyright © 2010 Pearson Education, Inc. Lectures prepared by Christine L. Case Chapter 8 Microbial Genetics
Copyright © 2010 Pearson Education, Inc. Q&A E. coli is found naturally in the human large intestine, and there it is beneficial. However, the strain designated E. coli O157:H7 produces Shiga toxin. How did E. coli acquire this gene from Shigella?
Copyright © 2010 Pearson Education, Inc. Structure and Function of Genetic Material 8-1Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics. 8-2Describe how DNA serves as genetic information. 8-3Describe the process of DNA replication. 8-4Describe protein synthesis, including transcription, RNA processing, and translation. 8-5Compare protein synthesis in prokaryotes and eukaryotes. Learning Objectives
Copyright © 2010 Pearson Education, Inc. Terminology Genetics: The study of what genes are, how they carry information, how information is expressed, and how genes are replicated Gene: A segment of DNA that encodes a functional product, usually a protein Chromosome: Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes Genome: All the genetic information in a cell
Copyright © 2010 Pearson Education, Inc. Terminology Genomics: The molecular study of genomes Genotype: The genes of an organism Phenotype: Expression of the genes
Copyright © 2010 Pearson Education, Inc. Clinical Focus, p. 223 Determine Relatedness
Copyright © 2010 Pearson Education, Inc. Determine Relatedness Strain % Similar to Uganda Kenya71% U.S.51% Which strain is more closely related to the Uganda strain?
Copyright © 2010 Pearson Education, Inc. Figure 8.1a E. coli
Copyright © 2010 Pearson Education, Inc. Figure 8.1b Genetic Map of the Chromosome of E. coli
Copyright © 2010 Pearson Education, Inc. Figure 8.2 The Flow of Genetic Information
Copyright © 2010 Pearson Education, Inc. Figure 8.3b DNA Polymer of nucleotides: Adenine, thymine, cytosine, and guanine Double helix associated with proteins "Backbone" is deoxyribose-phosphate Strands are held together by hydrogen bonds between AT and CG Strands are antiparallel
Copyright © 2010 Pearson Education, Inc. Figure 8.3a Semiconservative Replication
Copyright © 2010 Pearson Education, Inc. Figure 8.4 DNA Synthesis
Copyright © 2010 Pearson Education, Inc. DNA Synthesis DNA is copied by DNA polymerase In the 5' 3' direction Initiated by an RNA primer Leading strand is synthesized continuously Lagging strand is synthesized discontinuously Okazaki fragments RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase
Copyright © 2010 Pearson Education, Inc. Table 8.1
Copyright © 2010 Pearson Education, Inc. Table 8.1
Copyright © 2010 Pearson Education, Inc. Figure 8.5 DNA Synthesis
Copyright © 2010 Pearson Education, Inc. Figure 8.6 Replication of Bacterial DNA
Copyright © 2010 Pearson Education, Inc. ANIMATION DNA Replication: Replication Proteins ANIMATION DNA Replication: Overview ANIMATION DNA Replication: Forming the Replication Fork Replication of Bacterial DNA
Copyright © 2010 Pearson Education, Inc. Check Your Understanding Give a clinical application of genomics. 8-1 Why is the base pairing in DNA important? 8-2 Describe DNA replication, including the functions of DNA gyrase, DNA ligase, and DNA polymerase. 8-3
Copyright © 2010 Pearson Education, Inc. Transcription DNA is transcribed to make RNA (mRNA, tRNA, and rRNA) Transcription begins when RNA polymerase binds to the promoter sequence Transcription proceeds in the 5' 3' direction Transcription stops when it reaches the terminator sequence
Copyright © 2010 Pearson Education, Inc. Figure 8.7 Transcription
Copyright © 2010 Pearson Education, Inc. Figure 8.7 The Process of Transcription
Copyright © 2010 Pearson Education, Inc. Figure 8.7 ANIMATION Transcription: Overview ANIMATION Transcription: Process The Process of Transcription
Copyright © 2010 Pearson Education, Inc. Figure 8.11 RNA Processing in Eukaryotes
Copyright © 2010 Pearson Education, Inc. Figure 8.2 Translation mRNA is translated in codons (three nucleotides) Translation of mRNA begins at the start codon: AUG Translation ends at nonsense codons: UAA, UAG, UGA
Copyright © 2010 Pearson Education, Inc. Figure 8.2 The Genetic Code 64 sense codons on mRNA encode the 20 amino acids The genetic code is degenerate tRNA carries the complementary anticodon
Copyright © 2010 Pearson Education, Inc. ANIMATION Translation: Overview ANIMATION Translation: Genetic Code ANIMATION Translation: Process The Genetic Code
Copyright © 2010 Pearson Education, Inc. Figure 8.8 The Genetic Code
Copyright © 2010 Pearson Education, Inc. Figure 8.10 Simultaneous Transcription & Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation
Copyright © 2010 Pearson Education, Inc. Check Your Understanding What is the role of the promoter, terminator, and mRNA in transcription? 8-4 How does mRNA production in eukaryotes differ from the process in prokaryotes? 8-5
Copyright © 2010 Pearson Education, Inc. The Regulation of Gene Expression 8-6Define operon. 8-7Explain the regulation of gene expression in bacteria by induction, repression, and catabolite repression. Learning Objectives
Copyright © 2010 Pearson Education, Inc. Regulation Constitutive genes are expressed at a fixed rate Other genes are expressed only as needed Repressible genes Inducible genes Catabolite repression
Copyright © 2010 Pearson Education, Inc. Figure 8.12 ANIMATION Operons: Overview Operon
Copyright © 2010 Pearson Education, Inc. Figure 8.12 Induction
Copyright © 2010 Pearson Education, Inc. Figure 8.12 Induction
Copyright © 2010 Pearson Education, Inc. Figure 8.13 Repression
Copyright © 2010 Pearson Education, Inc. Figure 8.13 ANIMATION Operons: Induction ANIMATION Operons: Repression Repression
Copyright © 2010 Pearson Education, Inc. Figure 8.14 (a) Growth on glucose or lactose alone (b) Growth on glucose and lactose combined Catabolite Repression
Copyright © 2010 Pearson Education, Inc. Lactose present, no glucose Lactose + glucose present Figure 8.15
Copyright © 2010 Pearson Education, Inc. Check Your Understanding What is an operon? 8-6 What is the role of cAMP in catabolite repression? 8-7
Copyright © 2010 Pearson Education, Inc. Mutation: Change in the Genetic Material 8-8Classify mutations by type. 8-9Define mutagen. 8-10Describe two ways mutations can be repaired. 8-11Describe the effect of mutagens on the mutation rate. 8-12Outline the methods of direct and indirect selection of mutants. 8-13Identify the purpose of and outline the procedure for the Ames test. Learning Objectives
Copyright © 2010 Pearson Education, Inc. 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 © 2010 Pearson Education, Inc. Base substitution (point mutation) Missense mutation Mutation Change in one base Result in change in amino acid Figure 8.17a, b
Copyright © 2010 Pearson Education, Inc. Nonsense mutation Mutation Results in a nonsense codon Figure 8.17a, c
Copyright © 2010 Pearson Education, Inc. Mutation Frameshift mutation Insertion or deletion of one or more nucleotide pairs Figure 8.17a, d
Copyright © 2010 Pearson Education, Inc. Spontaneous mutation rate = 1 in 10 9 replicated base pairs or 1 in 10 6 replicated genes Mutagens increase to 10 –5 or 10 –3 per replicated gene ANIMATION Mutations: Types The Frequency of Mutation
Copyright © 2010 Pearson Education, Inc. Figure 8.19a Chemical Mutagens
Copyright © 2010 Pearson Education, Inc. Figure 8.19b ANIMATION Mutagens Chemical Mutagens
Copyright © 2010 Pearson Education, Inc. Radiation Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone
Copyright © 2010 Pearson Education, Inc. Figure 8.20 Radiation UV radiation causes thymine dimers
Copyright © 2010 Pearson Education, Inc. Figure 8.20 Repair Photolyases separate thymine dimers Nucleotide excision repair ANIMATION Mutations: Repair
Copyright © 2010 Pearson Education, Inc. Selection Positive (direct) selection detects mutant cells because they grow or appear different Negative (indirect) selection detects mutant cells because they do not grow Replica plating
Copyright © 2010 Pearson Education, Inc. Figure 8.21 Replica Plating
Copyright © 2010 Pearson Education, Inc. Figure 8.22 Ames Test for Chemical Carcinogens
Copyright © 2010 Pearson Education, Inc. Figure 8.22 Ames Test for Chemical Carcinogens
Copyright © 2010 Pearson Education, Inc. Check Your Understanding How can a mutation be beneficial? 8-8 How are mutations caused by chemicals? By radiation? 8-9 How can mutations be repaired? 8-10 How do mutagens affect the mutation rate? 8-11 How would you isolate an antibiotic-resistant bacterium? An antibiotic-sensitive bacterium? 8-12 What is the principle behind the Ames test? 8-13
Copyright © 2010 Pearson Education, Inc. Genetic Transfer and Recombination 8-14Differentiate horizontal and vertical gene transfer. 8-15Compare the mechanisms of genetic recombination in bacteria. 8-16Describe the functions of plasmids and transposons. Learning Objectives
Copyright © 2010 Pearson Education, Inc. Vertical gene transfer: Occurs during reproduction between generations of cells. Horizontal gene transfer: The transfer of genes between cells of the same generation. ANIMATION Horizontal Gene Transfer: Overview Genetic Recombination
Copyright © 2010 Pearson Education, Inc. Figure 8.23 Genetic Recombination Exchange of genes between two DNA molecules Crossing over occurs when two chromosomes break and rejoin
Copyright © 2010 Pearson Education, Inc. Figure 8.25 Genetic Recombination
Copyright © 2010 Pearson Education, Inc. Figure 8.24 ANIMATION Transformation Genetic Transformation
Copyright © 2010 Pearson Education, Inc. Figure 8.26 Bacterial Conjugation
Copyright © 2010 Pearson Education, Inc. Figure 8.27a Conjugation in E. coli
Copyright © 2010 Pearson Education, Inc. Figure 8.27b Conjugation in E. coli
Copyright © 2010 Pearson Education, Inc. Figure 8.27c ANIMATION Hfr Conjugation ANIMATION Chromosome MappingANIMATION F Factor ANIMATION Conjugation: Overview Conjugation in E. coli
Copyright © 2010 Pearson Education, Inc. ANIMATION Generalized Transduction Figure 8.28 ANIMATION Specialized Transduction Transduction by a Bacteriophage
Copyright © 2010 Pearson Education, Inc. Q&A E. coli is found naturally in the human large intestine, and there it is beneficial. However, the strain designated E. coli O157:H7 produces Shiga toxin. How did E. coli acquire this gene from Shigella?
Copyright © 2010 Pearson Education, Inc. 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 © 2010 Pearson Education, Inc. Figure 8.29 R Factor, a Type of Plasmid
Copyright © 2010 Pearson Education, Inc. Figure 8.30a, b Transposons Segments of DNA that can move from one region of DNA to another Contain insertion sequences for cutting and resealing DNA (transposase) Complex transposons carry other genes
Copyright © 2010 Pearson Education, Inc. Figure 8.30c Transposons
Copyright © 2010 Pearson Education, Inc. ANIMATION Transposons: Complex Transposons ANIMATION Transposons: Insertion Sequences ANIMATION Transposons: Overview Transposons
Copyright © 2010 Pearson Education, Inc. Check Your Understanding Differentiate horizontal and vertical gene transfer Compare conjugation between the following pairs: F + F –, Hfr F – What types of genes do plasmids carry? 8-16
Copyright © 2010 Pearson Education, Inc. Genes and Evolution 8-17Discuss how genetic mutation and recombination provide material for natural selection to act upon. Learning Objective
Copyright © 2010 Pearson Education, Inc. Genes and Evolution Mutations and recombination provide diversity Fittest organisms for an environment are selected by natural selection
Copyright © 2010 Pearson Education, Inc. Clinical Focus, p. 223 Evolution
Copyright © 2010 Pearson Education, Inc. Evolution Strain % Similar to Uganda Kenya71% U.S.51% Which strain is more closely related to the Uganda strain? How did the virus change?
Copyright © 2010 Pearson Education, Inc. Check Your Understanding Natural selection means that the environment favors survival of some genotypes. From where does diversity in genotypes come? 8-17