Biochemistry 2280A Lecture Notes - Lecture 17: Lac Repressor, Escherichia Coli, Enzyme
22 Nov 2017
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Document Summary
Regulation of gene expression: how are different bacterial promoters transcribed at different levels, not all genes are expressed at the same level, some sequences have better -10 and -35 sequences. Dna: trp repressor- acts as a dimer, has 2 fold symmetry, top part is mirror image of bottom, contact through helix 3. Dna- fits in adjacent major grooves: protein does not bind tightly to dna when there is lack of trp- helices move towards each other. Genetics has been critical in understanding the regulation of the trp operon: rna polymerase will access the promoter at all times if a mutation in the operator inhibits binding of the repressor. Lac operon- expression is required for the metabolism of lactose (fig 8-9: negative control: lac repressor, positive control: catabolite activator protein (cap) Catabolite repression: all cells metabolize glucose over other carbon sources, they shut off the genes required to metabolize other carbon sources in the presence of glucose.
