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Control of Prokaryotic (Bacterial) Genes Different from Eukaryotes!

Control of Prokaryotic (Bacterial) Genes Different from Eukaryotes!. Bacterial metabolism. Bacteria need to respond quickly to changes in their environment if they have enough of a product, need to stop production why? waste of energy to produce more

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Control of Prokaryotic (Bacterial) Genes Different from Eukaryotes!

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  1. Control of Prokaryotic (Bacterial) Genes Different from Eukaryotes!

  2. Bacterial metabolism • Bacteria need to respond quickly to changes in their environment • if they have enough of a product, need to stop production • why? waste of energy to produce more • if they find new food/energy source, need to utilize it quickly • why? metabolism, growth, reproduction • how? start production of enzymes for digestion STOP GO

  3. Bacteria group genes together • Operon • genes grouped together with related functions • example: all enzymes in a metabolic pathway • promoter = RNA polymerase binding site • single promoter controls transcription of all genes in operon • transcribed as one unit & a single mRNA is made • operator = DNA binding site of repressor protein

  4. So how can these genes be turned off? • Repressor protein – shuts down activity • binds to DNA at operator site • blocking RNA polymerase • blocks transcription – no proteins!

  5. trp RNA polymerase RNA polymerase repressor repressor repressor enzyme1 1 enzyme2 2 enzyme3 3 enzyme4 4 promoter repressor protein operator tryptophan trp trp trp trp trp trp trp trp trp tryptophan – repressor protein complex Repressible operon: tryptophan Synthesis pathway model When excess tryptophan is present, it binds to tryp repressor protein & triggers repressor to bind to DNA • blocks (represses) transcription gene1 gene2 gene3 gene4 TATA DNA mRNA trp conformational change in repressor protein! trp

  6. Remember lactose? Milk sugar • Lactose is a disaccharide that breaks down to the monosaccharides glucose and galactose. Bacteria has to make the enzyme to digest it when milk is present.

  7. RNA polymerase RNA polymerase repressor repressor repressor enzyme1 1 enzyme2 2 enzyme3 3 enzyme4 4 promoter repressor protein operator lactose lac lac lac lac lac lac lac lactose – repressor protein complex Inducible operon: lactose Digestive pathway model When lactose is present, binds to lac repressor protein & triggers repressor to release DNA • induces transcription lac gene1 gene2 gene3 gene4 TATA DNA mRNA lac conformational change in repressor protein! lac

  8. Operon summary • Repressible operon • usually functions in anabolic pathways • synthesizing end products • when end product is present in excess, shuts down so cell allocates resources to other uses • Inducible operon • usually functions in catabolic pathways, • digesting nutrients to simpler molecules • produce enzymes only when nutrient is available • cell avoids making proteins that have nothing to do, cell allocates resources to other uses

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