BIO206H5 Study Guide - Final Guide: Lac Repressor, Allolactose, Repressor
Document Summary
Bio206 tut0113: the laci gene product is a repressor protein. It prevents transcription of the lac operon: the repressor protein will bind to the operator sequence, located between the promoter and the start site of transcription on the lac operon. Initially, a dimer is formed, and, in the absence of lactose, it binds to the operator region of the operon. There are 3 binding sites for the dimer to bind: one main operator site and two auxiliary sites. If two of these sites are occupied, the dna is looped such that the dimers can form a tetramer. This bend of the dna prevents the binding of the rna polymerase: when present, lactose is transported into the cell. Once inside, the -galactosidase (lacz gene product) converts the lactose into allolactose. These genes are under positive control mechanism and their proteins code for basic metabolic machinery and other proteins necessary for cell life.
