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?