Question

Choose the correct answer from the alternatives given :
The sequence of structural genes in lac operon is

• A. Lac A, Lac Y. Lac Z
• B. Lac A, Lac Z, Lac Y
• C. Lac Y, Lac Z, Lac A
• D. Lac Z, Lac Y, Lac A

Answer 1

The correct option is D Lac Z, Lac Y, Lac A

The lac operon consists of three structural genes (lac Z, lac Y, lac A). Lac Z codes for 13-galactosidase which hydrolyses lactose to glucose and galactose. LacY codes for lac permease, a membrane-bound protein constituent of the lactose transport system which increase permeability of the cell to 13-galactosides. Lac A codes of thiogalactoside transacetylase, an enzyme of uncertain metabolic function. The appearance of ~3-galactosidase is coordinated with the production of permease and transacetylase. Operator gene is a gene which directly controls the synthesis of mRNA over the structural genes. Repressor is regulator protein synthesised all the time (constitutively) by the regulator igene. Repressor is meant for blocking the operator gene so that the structural genes are unable to form mRNAs. After coming in contact with inducer (e.g., lactose) the repressor undergoes conformational change in such a, way that it is unable to combine with operator. Thus, formation of inducer-repressor complex switches on the lac operon.

So, the correct answer 'Lac Z, Lac Y, Lac A'.