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Index >> Regulation of Protein Synthesis - Operon >> Control Mechanism - Induction

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Regulation of Protein Synthesis - Operon Structural Genes Operator Genes Promoter Gene Regulator Gene Control Mechanism - Induction Control Mechanism - Repression Inducible System Repressible System Negative Control of Protein Synthesis Positive Control of Protein Synthesis Mutation in the Operon

Control Mechanism - Induction

	Control Mechanism - Induction - A category of enzymes called inducible enzymes are normally absent from tbe cell or are present in very small quantities. They increase in quantity only in tbe presence of an inducer. Such a system is called an inducible system. A bacterial culture of E.coli growing in a medium with glucose as the source of carbon produces only minute quantities of the enzyme β-galactosidase.
Only one or two molecules of the enzyme are present. When lactose is added to the medium the production of β -galactosidase starts, and within two to three minutes about 3,000 molecules are synthesized by the Z gene. β -galactosidase hydrolyses lactose into the sugars galactose and glucose. Some galactose and glucose molecules are converted into allolactose, which is the inducer for β -galactosidase synthesis. In the lac system allolactose is the actual inducer while lactose is the apparent inducer. An artificial inducer commonly used is experimental work is isopropylthiogalactoside (IPTG).
When the inducer is absent the active repressor protein produced by the regulator gene associates with the operator gene and blocks it. No transcription of mRNA by the structural genes can therefore take place, and hence there is no enzyme synthesis
Absence of the inducer may be due to the fact that is not present in the growth medium, or is not synthesized by the microorganism. When the inducer is present the active repressor binds to the inducer molecule to form a repressor inducer complex (R-I). A conformational change takes place in the repressor molecule, which is inactivated. This prevents binding to the operator, which is therefore not blocked. The structural genes transcribe mRNA, and enzyme synthesis takes place.

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Regulation of Gene Activity in Eukaryotes Frenster's Model of Gene Regulation Nonhistone Protein as Derepressors Britten Davidson Operon Operator Model Sensor Genes Producer Genes Integrator Genes Receptor Genes

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