Biomi 2900- Wk 12

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regulon

Back 1

group of non-contingous genes are regulated by single regulatory protein

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maltose regulon - maltose present

Back 2

1. maltose (coactivator/inducer) binds to activator protein
2. malT stimulates RNAP
3. RNAP binds to promoter --> transcription

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maltose regulon - maltose absent

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1. maltose doesn't bind to malT
2. malT doesnt stimulate RNAP
3. RANP doesn't bind to promoter --> transcription repressed

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alternate methods of gene regulation at transcriptional level

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1. quorum sensing
2. 2-component system

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quorum sensing

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1. gene expression of group of bacteria based on local density of bacterial population

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lux operon in Vibrio fischeri

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1. lux I synthesizes homoserine lactone (autoinducer)
2. homoserine lactone is moved outside the cell and enters other bacteria
3. lux R (activator) stimulates transcription in the presence of homoserine lactone

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two-component system

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enables cells to convert an exterior signal into a interior signal
1. signal binds to sensor kinase
2. sensor kinase autophosphorylates
3. kinase phosphorylates response regulator
4. regulator binds to operator and activates/repressors transcription

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bacillus subtilis

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senses negative environmental signals and triggers formation of endospores

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methods of gene regulation at translational level

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1. regulation by RNA III
2. regulation by the RNA transcript

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regulation by RNA III

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RNase III degrades the RNA III/RNA transcript segment, terminating translation

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Regulation by RNA transcript

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signal molecules interacts with RNA transcript near rbs, and alters the location of the start codon and rbs- interferes with translation

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mutation

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change in DNA sequence that are spontaneous or induced

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types of mutations

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1. frameshitft (caused by insertion/deletion)
2. nonsense mutation (code for premature stop codon; caused by frameshift)
3. substitution/point mutation (replacement of one nucleotide)
4. silent mutation (point mutation that codes for the same aa and has no effect on protein)
5. missense mutation (point mutation that codes for different aa and causes faulty protein)

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causes for mutations

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1. damage to DNA (UV light creates thymine dimers
2. errors during DNA replication
3. spontaneous chemical changes (deamination, isomerization, base analogs, peroxides)
4.

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error free repair mechanisms

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1. mismatch repair (enzyme scans unmethylated daughter strand for nicks and replaces with DNA poly III)
2. base excision repair (BER) repair of a single damaged base
3. nucleotide excision repair (NER) repairs patches of damaged bases and uses poly I to repair
4. recombinational repair (used to correct dimers, using homologous recombination- gap is left on the undamaged strand and repaired via NER)

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error prone

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1. last resort (occurs when the cell is on the verge of death)
2. used when DNA damage is maximal
3. very imprecise (insert random base)

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Ames test

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1. identifies carcinogenic chemicals
2. "His +" "His -" indicates whether strain can synthesize histidine
3. if "His +" grows on "His -" medium, then it contained the mutagen that allowed for it to grow

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wild type

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most phenotypically common form of species in nature

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genetic selection

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selected growth conditions favor growth of a desired mutant strain and disfavor growth of wild type

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genetic screening

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all bacterial strains are grown and desired strains are identified by testing (ex: replica plating)

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Ways bacteria transfer DNA

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1. transformation (uptake of naked DNA into bacteria)
2. transduction (virus mediated transfer of DNA)
3. conjugation (transmission of DNA via cell-to-cell contact)