ch 8
TRANSCRIPT
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?
Clinical Focus, p. 223
Determine Relatedness
Determine Relatedness
Strain % Similar to Uganda
Kenya 71%
U.S. 51%
• Which strain is more closely related to the Uganda strain?
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
Figure 8.1b
Genetic Map of the Chromosome of E. coli
Figure 8.2
The Flow of Genetic Information
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.
Figure 8.3a
Semiconservative Replication
Figure 8.4
DNA Synthesis
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
Figure 8.7
Transcription
Figure 8.7
The Process of Transcription
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.
Figure 8.8
The Genetic Code
Figure 8.10
Simultaneous Transcription & 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
The Process of Translation
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
Figure 8.12
ANIMATION Operons: Overview
Operon
Figure 8.12
Induction
Figure 8.12
Induction
Figure 8.13
Repression
Figure 8.13
ANIMATION Operons: Induction
ANIMATION Operons: Repression
Repression
Figure 8.14
(a) Growth on glucose or lactose alone (b) Growth on glucose and lactose combined
Catabolite Repression
• 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
Figure 8.25
Genetic Recombination
Figure 8.24
ANIMATION Transformation
Genetic Transformation
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.
Figure 8.26
Bacterial Conjugation
Figure 8.27a
Conjugation in E. coli
Figure 8.27b
Conjugation in E. coli
Figure 8.27c
Conjugation in E. coli
Transduction
• DNA is passed from one bacterium to another in a bacteriophage and put into recipients DNA.
Figure 8.28
Transduction by a Bacteriophage
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
• Base substitution (point mutation)
• Missense mutation
Mutation
• Change in one base
• Result in change in amino acid
Figure 8.17a, b
• Nonsense mutation
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
Figure 8.19a
Chemical Mutagens
Radiation
• Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone
Figure 8.20
Radiation
• UV radiation causes thymine dimers
Figure 8.20
Repair• Photolyases separate thymine dimers
• Nucleotide excision repair
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
Figure 8.21
Replica Plating
Figure 8.22
Ames Test for Chemical Carcinogens
The old and new genetics
• Screening and selection of mutants
What do you think we would call the new genetics?