Question

The sequence of structural genes in lac operon is

• A. $LacA,LacY,LacZ$
• B. $LacA,LacZ,LacY$
• C. $LacY,LacZ,LacA$
• D. $LacZ,LacY,LacA$

Answer 1

Answer: (D)

The lac operon consists of three structural genes ($lacZ,lacXlacA$). $LacZ$ codes for $\beta$ -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 $\beta$-galactosides. $LacA$ codes of thiogalactoside transacetylase, an enzyme of uncertain metabolic function.