A) y, a and z cistrons
B) a, y and z cistrons
C) z, a and y cistrons
D) z, y and a cistrons
Correct Answer: D
Solution :
Lac Operon (Inducible Operon) is system that regulated gene expression which remains switched off normally but becomes operational in the presence of an inducer. It occurs in catabolic pathway. The components are (i) Structural genes These are genes, which produce mRNAs for forming polypeptide/ proteins/enzymes. The three structural genes are: Z : (produces enzyme p-galactosidase for splitting lactose/ galactoside into glucose and galactose) Y : (produces enzyme galactoside permease required for entry of lactose/ galactoside) and A : (produces enzyme galacoside acetylase/transacetylase). (ii) Operator gene It gives passage to RNA polymerase, when the structural genes are to express themselves. (iii) Promoter gene It is recognition centre/ initiation point for RNA polymerase of the operon. (iv) Regulator gene It produces a represser that binds to operator gene for keeping it non-functional. (v) Represser It is a small protein formed b regulator gene, which binds to operater gene and block passage of RNA polymerase towards structural genes. (vi) Inducer It is a chemical, which attaches to represser change the shape of operator binding site so that represser no more remain attached to operator.
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