The Lac Operon

Also called

lac operon · operon · gene regulation · gene expression · repressor · operator · promoter · inducer · lactose · beta-galactosidase · permease · transacetylase · polycistronic mRNA · Jacob and Monod · E. coli · negative regulation · लैक ओपेरॉन · दमनकारी प्रोटीन · प्रेरक

Topics

• An operon is a set of genes switched on and off together; the lac operon of E. coli handles lactose.
• The regulator gene i is always active: it makes the repressor protein.
• With no lactose the repressor sits on the operator and blocks RNA polymerase, so z, y and a stay off.
• Lactose is the inducer: it binds the repressor, which changes shape and lets go of the operator.
• RNA polymerase then binds the promoter and transcribes z, y and a into one polycistronic mRNA.
• z codes for β-galactosidase, which splits lactose into glucose and galactose.
• y codes for permease, which lets lactose into the cell; a codes for transacetylase.
• When the lactose is used up the repressor binds the operator again and the genes switch off.
• Jacob and Monod described the lac operon; control by a repressor is called negative regulation.

About this model

A GLB file of about 527 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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