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Lecture 33

BIO 202 Lecture 33: Prokaryote Gene Expression

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Stony Brook University
BIO 202

Regulation of Gene Expression Prokaryotes - Depends on whether transcription takes place - Prokaryotes and eukaryotes alter gene expression in response to their changing environment - Natural selection has favored bacteria that produce only the products needed by that cell - Dependent on the types of nutrition they can absorb - If tryptophan levels stay high, the cell can stop synthesizing additional enzymes in this pathway by blocking transcription of the genes for these enzymes - Tryptophan is a biosynthetic pathway - High levels of tryptophan can inhibit the enzyme that is required to synthesized tryptophan Operon: consists of 1. The genes that it controls: in bacteria, the genes coding for the enzymes of a particular pathway are often clustered together and transcribed as a single long mRNA molecule [polycistronic message] 2. The promoter where RNA polymerase binds. a. A single promoter regulates the synthesis of one polycistronic mRNA 3. An operator which acts as an “on-off switch”, lies between the promoter and the first gene. Operons allow coordinated regulation of related gene products Examples of Operons 1. Metabolizing Lactose [Catabolic pathway -Lactose is the starting product] a. Glucose is the preferred carbon source for E. coli. Uses lactose only when glucose is used up b. E. coli m
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