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
Correct Answer: D
Solution :
The structural genes direct synthesis of cellular proteins through mRNA and determine the sequence of amino acids in the proteins synthesized. The lac operon model of the bacterium Escherichia coli is a small segment of a circular DNA molecule which constitutes most of the genetic material of the bacterium. It has three structural genes Z, Y and A, which transcribe one long polycistronic mRNA molecule. This controls the synthesis of three different enzymes-\[\text{ }\!\!\beta\!\!\text{ -}\]galactosidase, galactosidase per -mease and galactoside transacetylase. \[\text{ }\!\!\beta\!\!\text{ -}\]galactosidase is the enzyme that splits lactose into glucose and galactose. Galactoside pern-lease facilitates the entry of lactose into the cell. Galactoside acetylase appears in small quantities upon lactose induction.
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