BCHM 218 Study Guide - Quiz Guide: Camp Receptor Protein, Catabolite Repression, Galactoside
7 Dec 2015
School
Department
Course
Professor
Document Summary
Transcription is a common site of regulation as the cell attempts to be as efficient. Functionally related genes cluster in operons where they can be controlled by a as possible single promoter. Lac operon is subject to negative regulation: lac operon encodes: Galactosidase (lacz): cleaves lactose glucose and galactose. Galactoside permease (lacy): acts as channel through the cell membrane and imports lactose into the cell. Transcribed from its own promoter: laco: this is the operator to which the lac repressor binds. Dna recognition occurs in the major groove by means of a helix- turn-helix motif which increases the dna"s flexibility. Transcriptional repression by the lac repressor is not absolute. Basal level of transcription is essential to operon regulation. Each cell always has a few molecules of -galactosidase and thiogalactoside transacetylase (to allow entry of lactose: when lactose is present, a small amount of allolactose (isomer of lactose) is produced the lac operon.
