Question

Lac operon model was proposed by
A) Jacob and Monod
B) Jacob and wollman
C) Jacob and Nirenberg
D) Jacob and Wilkins

Answer 1

A cluster of three structural genes encoding the proteins involved in lactose metabolism and the DNA sites involved in operon regulation is the Escherichia coli lactose or lac operon.

Complete answer:
In bacteria, many protein-coding genes are clustered together in operons that act as coordinately regulated transcriptional units.
In 1961, it was Jacob and Monod who proposed the operon model for transcription control.
Three elements are suggested by the operon model:

A selection of structural genes (i.e. genes which encode the proteins to be controlled);
Site of the operator, which is a DNA sequence that regulates structural gene transcription;
A regulator gene that encodes a protein that recognises the sequence of operators.
The Lac operon is one of the most studied operons. From E. coli.

Codes for the main enzymes involved in the metabolism of lactose:

Permease of galactosidase (also called permease of lactose).
It transports lactose through the cell membrane into the cell.
Galactosidase: Lactose hydrolysis into glucose and galactose.
Transacetylase of Thiogalactoside

Operon's Lac by E. Coli includes genes which are involved in lactose metabolism.. Only when lactose is present and glucose is absent is it conveyed.
In response to the levels of lactose and glucose, two regulators transform the operon on and off: the lac repressor and catabolite activator protein (CAP).
As a lactose regulator, the lac repressor works. It usually prevents the transcription of the operon, but when lactose is present, it stops functioning as a repressor.The lac repressor detects lactose indirectly via its isomer, allolactose.
Catabolite activator protein (CAP) functions as a glucose sensor. It stimulates the transcription of the operon, but only when the glucose level is low. Indirectly, via the CAMP "hunger warning" molecule, CAP detects glucose.

The correct answer is option (A) Jacob and Monod.

Note:
i) Regulatory gene I – codes for the protein of the repressor.
ii) Z gene – codes for beta-galactosidase that catalyses lactose hydrolysis into glucose and galactose.
iii) Y gene – It codes for permease that controls the permeability of the lactose in the cell.
a Gene – It codes for transacetylase, which supports the enzyme beta-galactosidase.
Both these genes assist in the metabolism of lactose. Lactose serves as an inducer in lac operon. If lactose is given to the bacteria in the medium, the regulatory gene is activated. The inducer binds to the repressor protein and makes it inactive, allowing the transcription of the operon. In this case, therefore, the lac operon is negatively regulated.