Understanding Lac Operon and IPTG Induction
For prokaryotes, genes are polycistronic – expression of multiple gene is mediated by one promoter. In bacteria such as E. coli, it appears that the products of carbohydrate metabolism themselves activate the switch between glucose and lactose use. When lactose is available , some molecules will be converted to allolactose inside the cell. Allolactose binds to the lac repressor and makes it change shape so it can no longer bind DNA. Allolactose is an example of an inducer, a small molecule that triggers expression of a gene or operon. Thus, RNA Polymerase will bind with promoter region of gene and starts transcription. On the other hand when lactose is absent , lac repressor binds with operator preventing RNA Polymerase to perform any further transcription. 1. If Both Glucose and Lactose are Present E. coli prefers to use glucose over lactose for energy. When glucose is present, it is metabolized first. The breakdown of glucose produces catabolites. These catabolites prevent the ...