Question

Which one is a structural gene in tryptophan operon ?

• A. trp K
• B. trp Z
• C. trp Y
• D. trp A

Hint:

Only one of these four gene names is a genuine structural gene of the trp operon.

Answer 1

The Correct Option is D

Step 1: The classic trp operon model in E. coli consists of a promoter, an operator, a leader sequence with an attenuator, and five structural genes named trpE, trpD, trpC, trpB and trpA in that order, all encoding enzymes of the tryptophan biosynthetic pathway.

Step 2: Among the four options given, only trpA matches one of these five real genes, coding for the alpha subunit of tryptophan synthase.

Step 3: trpK, trpZ and trpY do not correspond to any genuine gene in this operon and are invented names, so the correct answer is trp A.