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

Figure 8.13

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

Nonsense mutation

Mutation

Results in a nonsense codon

Figure 8.16a, c

Mutation

Frameshift mutation Insertion or deletion of one or more nucleotide pairs

Figure 8.16a, d

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

How could this happen???!!

What are transposons?

Jumping genes

Can be transferred to other cells