Chapter 8 Microbial Genetics

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					Chapter 8 Microbial Genetics
Biology 1009 Microbiology Johnson-Summer 2003

Structure and Function of Genetic Material
 DNA

& RNA  DNA=deoxyribonucleic acid  RNA=ribonucleic acid  Basic building blocks:  Nucleotides  Phosphate group  Pentose sugar  Nitrogenous base

Structure of DNA
Double stranded (double helix) Chains of nucleotides 5‟ to 3‟ (strands are anti-parallel) Complimentary base pairing
A-T G-C

DNA Structure
Phosphate-P Sugar-blue Bases-ATGC

DNA Replication
Bacteria have closed, circular DNA Genome: genetic material in an organism

E. coli
4 million base pairs 1 mm long (over 1000 times larger that actual bacterial cell) DNA takes up around 10% of cell volume

DNA Replication-occurs at the replication fork
5‟ to 3 „ DNA helicase-unzips + parental DNA strand that is used as a template
Leading stand (5‟ to 3‟-continuous) *DNA polymerase-joins growing DNA strand after nucleotides are aligned (complimentary) Lagging strand (5‟ to 3‟-not continuous)
*RNA polymerase (makes short RNA primer) *DNA polymerase (extends RNA primer then digests RNA primer and replaces it with DNA) *DNA ligase (seals Okazaki fragments-the newly formed DNA fragments)

Replication Fork

Protein Synthesis
DNA------- mRNA------ protein
transcription translation Central Dogma of Molecular Genetics

Transcription
One strand of DNA used as a template to make a complimentary strand of mRNA Promoter/RNA polymerase/termination site/5‟ to 3‟ Ways in which RNA & DNA differ:
RNA is ss RNA sugar is ribose Base pairing-A-U

Transcription

Types of RNA
Three types:
mRNA: messenger RNA
Contains 3 bases ( codon)

rRNA: ribosomal RNA
Comprises the 70 S ribosome

tRNA: transfer RNA
Transfers amino acids to ribosomes for protein synthesis Contains the anticodon (3 base sequence that is complimentary to codon on mRNA)

Genetic Code
DNA: triplet code
mRNA: codon (complimentary to triplet code of DNA) tRNA: anticodon (complimentary to codon)

Genetic Code
Codons: code for the production of a specific amino acid 20 amino acids 3 base code Degenerative: more than 1 codon codes for an amino acid Universal: in all living organisms

Genetic Code

Translation
Three parts:
Initiation-start codon (AUG) Elongation-ribosome moves along mRNA Termination: stop codon reached/polypeptide released and new protein forms

rRNA=subunits that form the 70 S ribosomes (protein synthesis occurs here) tRNA=transfers amino acids to ribosomes for protein synthesis)

Mutations
Changes in base sequence of DNA/lethal and inheritable Can be:
Harmful Lethal Helpful Silent

Normal DNA/Missense Mutation

Nonsense Mutation/Frameshift Mutation

Genetic Transfer in Bacteria
Genetic transfer-results in genetic variation Genetic variation-needed for evolution Three ways:
Transformation: genes transferred from one bacterium to another as “naked” DNA Conjugation: plasmids transferred 1 bacteria to another via a pilus Transduction: DNA transferred from 1 bacteria to another by a virus

Transduction by a Bacteriophage

Transformation

Conjugation in E. coli

Conjugation continued…

Conjugation continued…


				
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