Regulation by repression, induction and attenuation In addition to the mechanism above, the lac operon, as well as operons encoding enzymes involved in utilization of other energy sources, is regulated by catabolite repression , or the glucose effect- Glucose is the "preferred" energy source of E. coli ; it therefore makes sense not to synthesize enzymes such as those of the lac operon when glucose is present, even if lactose (or another energy source) is available- As shown in Tortora et al., Figure 8.15(a), E . coli grows more rapidly on gluclose than on lactose- The availability of glucose is signaled by intracellular levels of cyclic AMP = When glucose is readily available, cyclic AMP levels in the cell are low = When glucose becomes unavailable, the cell responds by synthesizing additional cyclic AMP- The lac operon has a site near the promoter called the CAP site , to which a protein called the catabolite activator protein (CAP) binds = Transcription of the lac
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This note was uploaded on 01/24/2012 for the course MCB MCB2010 taught by Professor Smith during the Fall '09 term at Broward College.