


















Microbial Genetics
What is the genetic material?
DNA
 Nucleotide base pairs
 A-T, C-G
 Chromosomes
 Bacteria: circular
 Chromatin
Genetics
 Genes
 Genome
 Genetic code
What is the purpose of DNA?
Recipe for making _____________
Genotype vs phenotype
What’s special about bacterial DNA?
Circular
Attached to PM at various pts
How is DNA copied for replication?
Recall DNA structure
Replication Overview
 DNA helicase unwinds double helix
 DNA polymerase III copies at replication fork
 Replication is 5’ to 3’
 Ligase “glues” nucleotides
 Animation
What is semiconservative replication?
What are the specifics of DNA replication?
DNA strands are antiparallel
Bidirectional replication animation
Rolling circle animation
Replication always starts at new 5’ end
 Leading strand
 Lagging strand
 Okazaki fragments (started with an RNA primer)

Error rate: 1 in 1010

Protein Synthesis










How does DNA direct protein synthesis?
Via RNA
 Three types of RNA
 tRNA, rRNA, mRNA
Overview:
 mRNA is copy of DNA gene
 Created by transcription
 Protein made during translation
 Ribosome “reads” triplet genetic code
 tRNA delivers appropriate amino acid
What happens in transcription?
mRNA created
 Often translation occurs while transcription happens
 Base pairing
 No T in RNA, instead U
 Begins with RNA polymerase attaching to promoter region of coding strand
 Stops when reaches terminator region
 transcription process
What happens in translation?
Ribosome attaches to mRNA
 Reads codons
 Code is redundant (degenerate)
 20 aas, but 61 codons
 3 stop codons (nonsense codes)
 Start codon (______) in bacteria codes for formylmethione
 tRNA brings in appropriate aa
 Matches to tRNA anticodon
How does the ribosome “read” the mRNA?
Ribosome finds start codon
 30S attaches, then 50S
 First tRNA to P site
 Second to A site
 First tRNA transfers aa to aa on A site tRNA
Ribosome shifts
 Moves 5’  3’
















New tRNA into now open A site
Process repeats
translation
How many ribosomes can work at once?
Is it the same process in eukaryotes?
Pretty much
Exception:


DNA is inside nucleus
Post-transcriptional modifications
 5’ cap
 3’ poly-A tail
 Introns removed
Control of Genes, Mutations and DNA Recombination
What controls gene expression?
Majority of genes are constitutive
 Protein produced at constant rate
Repression
 Inhibit gene expression
 Repressors: proteins that repress
Induction
 Turning on transcription
 Inducer: substance that induces
Lac operon model demonstrates these two processes
What is induction?
Induction
 Turning on transcription
 Inducer: substance that induces
Lac operon model demonstrates these two processes




What is repression?
Repression
 Inhibit gene expression
 Repressors: proteins that repress
What is the lac operon model?
Study of E. coli




















Inducible system when lactose is present
Three genes for lactose consumption
 next to each other on chromosome
 These are structural genes
 DNA nearby is control region
 Includes promoter and operator
 Together these are the operon
 Lac operon = 3 lac genes + operon region
 General regulation animation
 Animation
Regulation of Gene Expression
What happens if the DNA code is wrong?
Called a mutation

Causes change to mRNA sequence which can affect translation and thus
___________
Spontaneous
Induced
Excision repair
Mutation
Nonsense mutation
Results in a nonsense codon
Mutation
Frameshift mutation
Insertion or deletion of one or more nucleotide pairs
What types of mutation are there?
Original:

THE BIG FLY HAD ONE RED EYE.
Point mutation:

THE BIT FLY HAD ONE RED EYE.
Frame shift mutation:
Addition:
 THE BIT GFL YHA DON ERE DEY E.
Deletion of G in BIG:
 THE BIF LYH ADO NER EDE YE.
















Which is more dangerous?

mutations movie
Spontaneous mutations
Mutagens

Can affect pathogeneticity
What can be a mutagen?
Chemicals
 Nitrous acid
 Nucleoside analog
 Similar to normal nitrogenous base
 Causes mismatching of base pairs
 AZT (azidothymidine) does this
Radiation
 Formation of thymine dimers
 Light-repair enzymes (photolyases)
 animation
Mutagens vs Carcinogens: what the difference?
Mutagens
Carcinogens
Ames test
 Identifies possible carcinogens by identifying mutagens
 Looks to see how many mutate Salmonella cells revert to a nonmutant form
How can bacteria pass DNA?
Genetic recombination


Exchange of genes between chromosomes
Gives new combinations
Vertical gene transfer

Parent to offspring
Horizontal transfer

3 types…
What is conjugation?
Horizontal gene transfer (1% of population)
 Donor bacterial cell gives DNA to recipient cell


 Recipient now has recombinant DNA
Conjugation


Process in E. coli
 Donor is F+, recipient F F= fertility factor
 Hfr cell (high frequency of recombination
 When F factors integrate into chromosome
Conjugation-plasmid
Conjugation-chromosome

What is transduction?




Virus transfer DNA
general vs. specialized
animation

What is transformation?
Gene transferred to recipient bacterium
Griffith (1928)
 Studied Streptococcus pneumoniae
 Two strains: one virulent, one not
Transformation animation

What are transposons?




Jumping genes
Can be transferred to other cells