BIOS-115 Lecture Notes - Lecture 14: Lac Operon, Lac Repressor, Housekeeping Gene
4 Nov 2018
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Regulation of gene expression: regulated genes only active when needed, constitutive or housekeeping genes always active (essential processes) Gene expression is regulated distinctly in different cell types. Bacteria can use operons to regulate gene expression. Cluster of related genes that: (cid:3843) share a common operator (controlling site), (cid:3844) share a promoter, & (cid:3845) are transcribed onto a single polycistronic mrna. Operator dna sequence adjacent to promoter; bound by repressor. Repressor blocks rna polymerase promoter binding; no transcription. Repressor is encoded by laci adjacent to operon. A bacterial inducible operon: actively transcribed in the presence of lactose, proteins synthesized needed to use lactose as energy source. Inducible vs repressible genes: defined by response of operon to a metabolite (small molecule) Galactosidase: breaks down lactose into glucose and galactose. Lactose permease: membrane protein that actively transports lactose into cell. Lac repressor: negatively controls expression of the lac operon through binding at the operator. Operator: does not code for a protein product.
