Transcriptional control in prokaryotes
- Created by: Alice Fisher
- Created on: 07-05-15 20:52
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- 11 Transcriptionalcontrol in prokaryotes
- Bacteria
- Haploid; no gamete forming process. 'Crosses' can be made between genetically distinct bacteria
- Ecoli; mostly nonpathogenic, rapid growth rate, grows in simple liquids (broth) and on solid (agar) media
- Minimal medium = simple carbon source (sugar), salt, trace minerals
- Mutation that inactivates a biosynthetic pathway prevents growth on minimal medium
- Complete medium contrains all amino acids, vitamins and nucleotides produced by biosynthetic pathways so even mutated bacteria grow
- Minimal medium = simple carbon source (sugar), salt, trace minerals
- Bacteria carrying mutation involved in a specific biosynthetic pathway will grow on minimal medium and the biosynthetic product
- Inducing mutations and then growing on minimal medium will identify mutants. Changing composition can screen for genes involved in specific pathways.
- Mutants that cannot synthesis essential nutrients are autotrophs. Strains that are wild type for a specific biosynthetic process are phototrophs
- Gene transfer
- Requires cell cell contract. The fertility factor - the F plasmid
- Unidirectional; dna transferred across bridge
- Donor strands contains a fertility factor F+. Means carries are able to conjugate with F- recipient cells
- F plasmid transferred through the F-pilus 'Bacterial mating'
- Plasmid has an orIT where transfer begins and tra genes which encode components of the transfer machinery
- F plasmid transferred through the F-pilus 'Bacterial mating'
- Donor strands contains a fertility factor F+. Means carries are able to conjugate with F- recipient cells
- F factor can also cause transfer of host chromosomal genes from high frequency recombination (hfr) strains into F- strains
- Hfr strains arise when the F plasmid recombines with host chromosomalDNA. F plasmid integrated. These then conjugate with F- cells. Hfr donor chromosome is nicked and transferred to recipient cell which is recombined into recipitent chromosome
- Formation of hfr donor chromosomes allows the emergence of prototrophic colonies (requiring same nutrients) from a mixed culture of 2 different auxotrophic (inability to synthesise a product) mutants
- Hfr strains arise when the F plasmid recombines with host chromosomalDNA. F plasmid integrated. These then conjugate with F- cells. Hfr donor chromosome is nicked and transferred to recipient cell which is recombined into recipitent chromosome
- Metabolic gene regulation
- 1. Nutrient breakdown. Induction via nutrient e.g lactose. Enzyme encoding genes e.g. lac operon proteins. Breaksdown product e.g. to glucose. This repressed enzymes (negative feedback)
- 2. Biosynthesis.substrate leads to enzyme encoding genes. Makes biosynthetic product wich represses enzyme. Feedback inhibition
- The Trp operon; low trp - inactive trip repressor - trip synthesised; high trp - active trip repressor(rnapolymerase detaches) - transcription repressed
- Lac operon
- Operon = group of genes with closely related biochemical functions; multiple proteins synthesised from one mrna.
- Induced in response to lactose substrate and encodes its breakdown. Blocked with glucose
- Promoter, operator, B galactosidase gene, permease, transacetylase, terminator
- Lac repressor binds to operator blocking transcription. Lactose causes it to dissociate allowing CAP-assisted transcription by rna polymerase. Production of glucose inhibits by inactivating rna polymerase cos-factor CAP protein
- Bacteria
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