Ch8 microbial genetics

CH8: Microbial Genetics

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?

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

Structure and Function of Genetic Material

Terminology Genomics: The molecular study of genomes

(sequencing and molecular characterization of genomes).

Genotype: The genes of an organism Phenotype: Expression of the genes

The Flow of Genetic Information

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

Semiconservative Replication

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

DNA Synthesis

Replication of Bacterial DNA

Important Enzymes DNA GyraseDNA Helicase DNA polymerase

RNA and Protein SynthesisTranscription 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

Transcription

The Process of Transcription

ANIMATION Transcription: Overview

ANIMATION Transcription: Process

The Process of Transcription

RNA Processing in Eukaryotes

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

The Genetic Code

64 total codons of which 61 sense codons encode the 20 amino acids

3 are non-sense codons or stop codons.

The genetic code is degenerate

tRNA carries the complementary anticodon

The Genetic Code

Simultaneous Transcription & Translation

Figure 8.9-1

Figure 8.9-2

Regulation Constitutive genes are expressed at a fixed rate

(60-80%genes) Other genes are expressed only as needed

Repressible genes: Always active , can be turned off (repressed).

Inducible genes: Inactive , needs to be turned on or induced.

Catabolite repression: Inhibition of the metabolism of alternative carbon sources by Glucose.

Regulation of protein synthesis saves (conserve) energy for the organism.

The Regulation of Gene Expression

Operon

Control of TranscriptionConsists of a promotor, an operator and series of genes

• Inducible operons – must be activated by inducers

• Regulate catabolic pathway

• Lactose Operon

• Repressible operons – transcribed continually until deactivated by repressors

• Regulate anabolic pathway.

• Tryptophan Operon

Operons

Induction

Repression

Lactose present, no Glucose

Lactose + glucose present

Figure 8.15

Catabolite Repression

Figure 8.14b

Mutation

A change in the genetic material Mutation is a change in the base sequence of DNA. 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

Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes

Mutagens increase to one in 105(10-5) or one in 103(10–3) per replicated gene

Point mutations concept map

The Frequency of Mutation

Chemical Mutagens

Nucleoside analogs

Chemical mutagens

Frameshift mutagens Cause small deletions or insertions Ex:Benzopyrene in smoke Aflatoxins Acridine orange

Frameshift mutagens are often carcinogens.

Radiation

Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone

Causes physical breakdown of DNA

Radiation

UV radiation causes thymine dimers

Repair Photolyases separate thymine dimers Nucleotide excision repair (can repair other

mutations also)

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

Ames Test for Chemical Carcinogens

90% of the chemicals found to be mutagenic also have been shown to be carcinogenic.

• Exchange of DNA segments composed of homologous sequences

• Recombinants – cells with DNA molecules that contain new nucleotide sequences

• Vertical gene transfer – organisms replicate their genomes and provide copies to descendants

• Horizontal gene transfer – donor contributes part of genome to recipient; three types

• Transformation

• Transduction

• Bacterial Conjugation

Genetic Recombination and Transfer

Vertical gene transfer: Occurs during reproduction between generations of cells.

Horizontal gene transfer: The transfer of genes between cells of the same generation.

Genetic Recombination

Exchange of genes between two DNA molecules Crossing over

occurs when two chromosomes break and rejoin

Genetic TransformationGriffith’s Experiment

• Griffiths experiment concluded transforming agent was DNA; one of conclusive pieces of proof that DNA is genetic material

• Cells that take up DNA are competent; results from alterations in cell wall and cytoplasmic membrane that allow DNA to enter cell

Transformation

Bacterial ConjugationTransfer of DNA by cell to cell contact

Transduction by a Bacteriophage• Generalized

transduction – transducing phage carries random DNA segment from donor to recipient

• Specialized transduction – only certain donor DNA sequences are transferred

Plasmids

Conjugative plasmid: Carries genes for sex pili and transfer of the plasmid

Dissimilation plasmids: Encode enzymes for catabolism of unusual compounds

Bacteriocins plasmids R factors: Encode antibiotic resistance

R Factor, a Type of Plasmid

Carry genes that confer resistance to antibiotics.

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

Genes and Evolution

Mutations and recombination provide diversity Fittest organisms for an environment are selected by

natural selection

Ch8 microbial genetics

Science

Transcript of Ch8 microbial genetics

MICROBIAL GENETICS INTRODUCTION TO GENETICS AND …

Microbial Genetics Central Dogma

Microbial Genetics

Microbial Genetics (Micr340)

29 Microbial Genetics

Chapter8 Microbial genetics

Microbial Genetics genomics

Microbial genetics mutation

Microbial Genetics 6

Microbial genetics Application microbial genetics ... · •Microbial Genotypes & Phenotypes –Microbial phenotypes are usually designated by a non italicized 3-letter abbreviation

(2) microbial genetics

Microbial Genetics

Introduction to Microbial Genetics

Microbial Growth & Genetics

MICROBIOLOGY - Houston Community College · 2015. 9. 20. · 4 (10/17) (Ch7) Microbial Genetics (10) Selective, Differential & Enriched Media (Ch8) Recombinant DNA Technology (11)

microbial genetics (2)instruction2.mtsac.edu/crexach/microbiology 1/pdf micro lectures... · Microbial genetics and reproduction Microbial genetics and reproduction By Dr. C. Rexach