Transcript Ch 8
Microbial Genetics The how and why of information flow in living things. What exactly is living? Genetics Terms • • • • • • • Genome: Chromosome Gene Base pair Genetic code Genotype Phenotype The Polymers of life • Define Polymer • Define Monomer • What are the polymers of life? • Why use polymers? Determine Relatedness Clinical Focus, p. 223 Determine Relatedness • Which strain is more closely related to the Uganda strain? Strain % Similar to Uganda Kenya 71% U.S. 51% The genetic Code • Name the monomers that make up the genetic code. • Name the monomers that make up Proteins What is the flow of genetic information in the bacterial cell? Verb Enzyme Substrate Product Genetic Map of the Chromosome of E. coli Figure 8.1b The Flow of Genetic Information Figure 8.2 DNA Replication • The double strand of DNA is separated. • DNA polymerase reads the DNA strand and creates another. • The newly synthesized DNA contains an old strand and a new strand. • The two new strands are then separated into the two new daughter cells. Semiconservative Replication Figure 8.3a DNA Synthesis Figure 8.4 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 Transcription • A sequence of DNA is relaxed and opened up. • RNA polymerase synthesizes a strand of RNA • RNA uses ACGU • Starting point is a promoter Transcription Figure 8.7 The Process of Transcription Figure 8.7 Translation • mRNA associates with ribosome's (rRNA and protein) • 3-base segments of mRNA specify amino acids and are called codons. • Genetic code: relationship among nucleotide sequence and corresponding DNA sequence. Degenerate: Most amino acids are code for by more than one codon. • • • • 64 codons 3 are nonsense Start codon Aug is for methionine. See the codon sequence. The Genetic Code Figure 8.8 Simultaneous Transcription & Translation Figure 8.10 The Process of Translation Figure 8.9 The Process of Translation Figure 8.9 The Process of Translation Figure 8.9 The Process of Translation Figure 8.9 The Process of Translation Figure 8.9 The Process of Translation Figure 8.9 The Process of Translation Figure 8.9 The Process of Translation Figure 8.9 Info • From information storage to reality. • What determines what info is used • What determines how information is moved about. Regulation • Constitutive genes are expressed at a fixed rate • Other genes are expressed only as needed – Repressible genes – Inducible genes – Catabolite repression Operon ANIMATION Operons: Overview Figure 8.12 Induction Figure 8.12 Induction Figure 8.12 Repression Figure 8.13 Repression ANIMATION Operons: Induction ANIMATION Operons: Repression Figure 8.13 Catabolite Repression (a) Growth on glucose or lactose alone (b) Growth on glucose and lactose combined Figure 8.14 • Lactose present, no glucose • Lactose + glucose present Figure 8.15 Types of Bacterial sex Name Process What it is Comments Genetic Recombination • The rearrangement of genes. • Crossing over is where genes are recombined within a chromosome. Transformation • Naked DNA is transferred from one bacteria to another. • Was the first experiment that showed DNA was the genetic information Genetic Recombination Figure 8.25 Genetic Transformation ANIMATION Transformation Figure 8.24 Conjugation • DNA transferred from one bacteria to another by a sex pillus. • Information of transfer coded by a plasmid called F+ • Hfr cells occur when F+ plasmid goes into the host chromosome and recombines, it will then draw across the DNA. Bacterial Conjugation Figure 8.26 Conjugation in E. coli Figure 8.27a Conjugation in E. coli Figure 8.27b Conjugation in E. coli Figure 8.27c Transduction • DNA is passed from one bacterium to another in a bacteriophage and put into recipients DNA. Transduction by a Bacteriophage Figure 8.28 Alternate forms of the chromosome format. • Plasmids: self replicating circular molecules of NDA • Transposes: small segments of DNA that can move into different parts of the genome. • Can these have an effect on Evolution? Control of gene expression • Repression • Induction The Operon Model of gene expression • Repression: regulatory mechanism inhibits gene expression • Induction: a process that turn on gene expression Repressible Operon Inducible operon Where are the points of control If a cell has all the genes that are needed then why are they not expressed at one time? Mutations • What are they? Mutations • What can they do 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 Mutation • Base substitution (point mutation) • Missense mutation • Change in one base • Result in change in amino acid Figure 8.17a, b Mutation • Nonsense mutation • Results in a nonsense codon Figure 8.17a, c Mutation • Frameshift mutation • Insertion or deletion of one or more nucleotide pairs Figure 8.17a, d The Frequency of Mutation Chemical Mutagens Figure 8.19a Radiation • Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribosephosphate backbone Radiation • UV radiation causes thymine dimers Figure 8.20 Repair • Photolyases separate thymine dimers • Nucleotide excision repair Figure 8.20 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 Replica Plating Figure 8.21 Ames Test for Chemical Carcinogens Figure 8.22 The old and new genetics • Screening and selection of mutants What do you think we would call the new genetics?