The ability to switch from glucose use to another substrate like lactose is a consequence of the activity of an enzyme called Enzyme IIA (EIIA). Malfunctions in this process in humans lead to the development of cancer and other diseases. Each nucleated cell in a multicellular organism contains copies of the same DNA. An early step in the regulatory functions of these proteins is their binding to specific DNA sequences within the lac promoter-operator region. Such operons are classified as either repressible operons or inducible operons. The lac operon is a good example of the negative control (negative regulation) of gene expression in that bound repressor prevents transcription of the structural genes. Similarly, all cells in two pure bacterial cultures inoculated from the same starting colony contain the same DNA, with the exception of changes that arise from spontaneous mutations. Landman J, Brewster RC, Weinert FM, Phillips R, Kegel WK. The binding of the small molecule determines which stem-loop structure forms, thus influencing the completion of mRNA synthesis and protein synthesis. What are the parts in the DNA sequence of an operon? The lac operon also plays a role in this switch from using glucose to using lactose. An operon is a functioning unit of genomic DNA that contains a group of genes controlled by a single promoter. During induction, the inducer binds to the repressor. The catabolite gene activator protein (CAP) and the lac repressor regulate the transcriptional activity of the lactose operon. The lacI gene has its own promoter (PlacI) that binds RNA polymerase and leads to transcription of lac repressor mRNA and hence the production of lac repressor protein monomers. Cyclic adenosine monophosphate (cAMP) is produced during glucose starvation, binds to CAP, and causes a conformational change that allows CAP to bind to a DNA site located adjacent to the lac promoter. Expression of this operon is activated only when lactose levels outside the cell are high and glucose levels are low. What is the name given to a collection of operons that can be regulated as a group? Textbook of Microbiology & Immunology. What are two ways that bacteria can influence the transcription of multiple different operons simultaneously in response to a particular environmental condition? It was Jacob and Monod in 1961 who proposed the operon model for the regulation of transcription. This model actually proposes two operators, O1 and O2 that are also the binding sites of AraC. What type of stimulus would trigger the transcription of a different σ factor?

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