Chapter 8Microbial Genetics
Biology 1009Microbiology
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 DNADouble stranded (double helix)Chains of nucleotides5’ to 3’ (strands are anti-parallel)Complimentary base pairing
A-TG-C
DNA Structure
Phosphate-PSugar-blueBases-ATGC
DNA ReplicationBacteria have closed, circular DNAGenome: genetic material in an organismE. coli
4 million base pairs1 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------" proteintranscription translation
Central Dogmaof Molecular Genetics
TranscriptionOne strand of DNA used as a template to make a complimentary strand of mRNAPromoter/RNA polymerase/termination site/5’ to 3’Ways in which RNA & DNA differ:
RNA is ssRNA sugar is riboseBase pairing-A-U
Transcription
Types of RNAThree types:
mRNA: messenger RNAContains 3 bases ( codon)
rRNA: ribosomal RNAComprises the 70 S ribosome
tRNA: transfer RNATransfers amino acids to ribosomes for protein synthesisContains the anticodon (3 base sequence that is complimentary to codon on mRNA)
Genetic CodeDNA: triplet code
mRNA: codon (complimentary to triplet code of DNA)
tRNA: anticodon (complimentary to codon)
Genetic CodeCodons: code for the production of a specific amino acid20 amino acids3 base codeDegenerative: more than 1 codon codes for an amino acidUniversal: in all living organisms
Genetic Code
TranslationThree parts:
Initiation-start codon (AUG)Elongation-ribosome moves along mRNATermination: 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)
MutationsChanges in base sequence of DNA/lethal and inheritableCan be:
HarmfulLethalHelpfulSilent
Normal DNA/Missense Mutation
Nonsense Mutation/Frameshift Mutation
Genetic Transfer in BacteriaGenetic transfer-results in genetic variationGenetic variation-needed for evolutionThree ways:
Transformation: genes transferred from one bacterium to another as “naked” DNAConjugation: 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…