Q.In E. coli, three enzymes beta-galactosidase, permease and transacetylase are produced in the presence of lactose. Explain why the enzymes are not synthesized in the absence of lactose.

Operons are clusters of functionally related genes, transcribed together under shared regulatory control, as in the bacterial lac operon.

In prokaryotes, genes coding for enzymes of a common metabolic pathway are frequently organised together on the chromosome as an operon -- a single transcriptional unit consisting of structural genes with related functions, along with a shared promoter and operator region that regulates their coordinated expression. The classic example is the lac operon in E. coli, described by Francois Jacob and Jacques Monod, in which the genes for lactose metabolism (lacZ, lacY, lacA) are transcribed together as one polycistronic mRNA. Recon and muton are older, now largely obsolete genetic terms referring respectively to the smallest unit of recombination and the sma …

The lac operon model of bacterial gene regulation was proposed by Jacob and Monod.

Jacob and Monod's operon concept explained how a cluster of functionally related genes (lacZ, lacY, lacA) in E. coli, along with a regulatory gene (lacI) and control elements (promoter, operator), could be switched on together in the presence of lactose and switched off in its absence -- a foundational model for understanding prokaryotic gene expression control, for which they (with Andre Lwoff) received the Nobel Prize. Hershey and Chase demonstrated that DNA (not protein) is the genetic material; Meselson and Stahl confirmed the semi- …