Question

An operon unit consist of
A. Regulator, operator and recessive gene
B. Regulator, structural and operator gene
C. Regulator, structural, operator and promoter gene
D. Regulator, structural and promoter gene.

Answer 1

Hint: Lac operon with its full name lactose operon is essential for metabolism and transport of lactose mainly in E-coli and many other bacteria. The lac operon involved in effective digestion of lactose when glucose is not available with the help of beta- galactosidase. The word “Lac” means the ability to use lactose.

Complete answer:
Lac operon consists of 3 structural genes i.e. z, y, a with one promoter, an operator and a terminator regulator, which are involved in metabolism of lactose. LacZ encodes for $\beta $-galactosidase an intracellular enzyme, LacY encodes for Beta- galactoside permease nd LacA encodes for Beta- galactoside transacetylase, an enzyme that transfers acetyl group from acetyl CoA to beta-galactosides. The three structural genes transcribe polycistronic mRNA to form three enzymes which are mentioned just above, the operator gene controls the working of structural genes. The promoter gene is the point where RNA is attached, the regulator gene codes for protein in the absence of lactose which is called a repressor that combines with the operator to suppress its activity. When the promoter gene is turned on by an inducer (Lactose) the cistrons are expressed. The lac operon uses two part control mechanisms for cells to expand energy by producing the enzymes encoded by lac operon.

So, the correct option is C.

Note: The repressor is an allosteric protein, it is a regulation of an enzyme that binds an effector molecule other than the active site of enzyme. The proteins are not produced by the bacterium when lactose is unavailable as a carbon source.