Microbial Genetics

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Microbial Genetics
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What is the genetic material?

• DNA
• Nucleotide base pairs
• A-T, C-G
• Chromosomes
• Bacteria circular
• Chromatin
• Genetics
• Genes
• Genome
• Genetic code

3
What is the purpose of DNA?

• Recipe for making _____________
• Genotype vs phenotype

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Whats special about bacterial DNA?

• Circular
• Attached to PM at various pts
• Topoisomerase II (DNA gyrase) supercoils it

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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

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What is semiconservative replication?
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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

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Protein Synthesis
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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

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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

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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

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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

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How many ribosomes can work at once?
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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

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Control of Genes, Mutations and DNA Recombination
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What controls gene expression?
OFF

• 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

ON
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What is the lac operon model?
OFF

• 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

ON
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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

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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

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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

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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

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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

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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

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What is transduction?

• Virus transfer DNA
• general vs. specialized
• animation

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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???!!
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What are transposons?

• Jumping genes
• Can be transferred to other cells