Microbial Genetics Chapter 8

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

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

DNA Replication w Bacteria have only 1 chromosome (ccDNA) w 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 w

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

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

Bidirectional replication w Origin of replication w Termination site

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

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

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

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

Genetic Code w DNA w mRNA w tRNA w Triplet code w codons w anticodons

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

Translation w rRNA ribosomal RNA (forms the ribosomes) (70S) w 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 w All Genes are not always being expressed w Genes turned on all the time - Constitutive w Other genes can be regulated: Turned On Turned Off

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

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

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

Types of Mutations Normal DNA

Base Substitution Mutation C Missense Mutation

T Nonsense Mutation Base Substitution Mutation

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

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

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

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

Griffith’s Experiment

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

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