microbial genetics

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Microbial Genetics:

Microbial Genetics Chapter 8

Structure and Function of Genetic Material:

Structure and Function of Genetic Material DNA & RNA DNA deoxyribonucleic acid RNA ribonucleic acid Nucleotides Phosphate group Pentose sugar Nitrogenous base

Structure of DNA:

Structure of DNA Double stranded (double helix) polymers of nucleotides 5’ to 3’ (strands are anti-parallel) Complimentary Base Pairing A - T G - C

DNA Replication:

DNA Replication Bacteria have only 1 chromosome (ccDNA) E. coli about 4 million base pairs 1 mm long (1000 times longer than the cell) DNA takes up only about 10 % of cells volume

Slide 7:

E. coli DNA 1u 1,360u 1ft. 1,360 ft.

DNA Replication occurs at the Replication Fork (5’ to 3’):

DNA Replication occurs at the Replication Fork (5’ to 3’) DNA Helicase 1. Leading Strand ( 5’ to 3’ ) DNA Polymerase 2. Lagging Strand ( 5’ to 3’) RNA Polymerase (RNA Primer) DNA Polymerase (extends primer and digests RNA) DNA Ligase Okazaki Fragments

Bidirectional replication:

Bidirectional replication Origin of replication Termination site

Protein Synthesis:

Protein Synthesis DNA mRNA Protein Transcription Translation Central Dogma of Molecular Genetics

Transcription:

Transcription One strand of DNA is used as a template to form a complimentary strand of mRNA mRNA ----> messenger RNA

Transcription:

Transcription 3 ways RNA differs from DNA Promoter RNA Polymerase Termination Site 5’ to 3’

3 Types of RNA:

3 Types of RNA 1. mRNA Contains the codons 2. rRNA Ribosomes (70S) 3. tRNA Transfer amino acids to the ribosomes for protein synthesis Anti-codon

Genetic Code:

Genetic Code DNA mRNA tRNA Triplet code codons anticodons

Genetic Code:

Genetic Code Codons code for a specific amino acid 20 amino acids 3 base code - 4 bases ( A,U,G,C ) 64 possible combinations ( 4 3 ) Amino acids are coded for by more than one codon Genetic Code is Degenerative Genetic Code is Universal

Translation:

Translation rRNA ribosomal RNA (forms the ribosomes) (70S) tRNA transfer RNA (transfers amino acids to the ribosomes for protein synthesis) anticodon 3 base sequence that is complimentary to the codon on mRNA

Regulation of Gene Expression:

Regulation of Gene Expression All Genes are not always being expressed Genes turned on all the time - Constitutive Other genes can be regulated: Turned On Turned Off

lac operon:

lac operon Lac - Lactose (dissacharide) Glucose and Galactose operon - series of structural genes all under the control of a Regulatory Gene lac operon is normally turned off lac operon is an Inducible operon

Tryptophan operon:

Tryptophan operon Tryptophan - amino acid operon - series of structural genes all under the control of a Regulatory Gene Tryptophan operon is normally turned on Tryptophan operon is a repressible operon

Mutations - a change in the base sequence of DNA:

Mutations - a change in the base sequence of DNA Mutations can be: 1. Harmful 2. Lethal 3. Beneficial 4. Silent (neutral) UUU - Phe UUC - Phe

Slide 28:

Types of Mutations Normal DNA

Slide 29:

Base Substitution Mutation C Missense Mutation

Slide 30:

T Nonsense Mutation Base Substitution Mutation

Frame Shift Mutation:

Frame Shift Mutation ATG CAT GCA TGC ATT TCC TGC TTA AAA 1. Addition Mutation A AT GCA TGC ATG CAT TTT CCT GCT TAA Reading Frame is Shifted 2. Deletion Mutation TGC ATG CAT GCA TTT CCT GCT TAA Reading Frame is Shifted

Genetic Transfer in Bacteria:

Genetic Transfer in Bacteria Genetic Transfer - results in Genetic Variation Genetic Variation - is needed for Evolution 3 Ways Genetic Transfer can occur in Bacteria 1. Transformation 2. Cunjugation 3. Transduction

Transformation:

Transformation Genes are transferred from one bacterium to another as “naked” DNA Frederick Griffith (1928)

Griffith’s Experiment:

Griffith’s Experiment 2 Strains of Streptococcus pneumoniae 1. Virulent strain with a capsule - Pneumonia 2. Avirulent strain without a capsule - no disease

Slide 35:

Griffith’s Experiment

Slide 36:

Griffith’s Experiment

Slide 37:

Griffith’s Experiment

Slide 38:

Griffith’s Experiment

Slide 40:

Conjugation One bacterium passes some DNA (in a plasmid) to another bacterium

Transduction:

Transduction DNA is transferred from one bacterium to another by a virus Bacteriophage virus that only infects bacteria

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