Question

Match List-I with List-II
List-I (Operon component):
(A). Promoter
(B). Operator
(C). Structural gene
(D). Regulatory gene
List-II (Role):
(I). Produces repressor protein
(II). Site where repressor binds
(III). Code for functional proteins
(IV). Binding site for RNA polymerase

• (A) - (IV), (B) - (II), (C) - (III), (D) - (I)
• (A) - (III), (B) - (I), (C) - (II), (D) - (IV)
• (A) - (IV), (B) - (III), (C) - (I), (D) - (II)
• (A) - (II), (B) - (III), (C) - (IV), (D) - (I)

Hint:

To remember:
- Promoter = RNA Polymerase binding
- Operator = Repressor binding
- Regulatory gene = Repressor synthesis

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
An operon is a functional unit of genomic DNA in prokaryotes that contains a cluster of genes under the control of a single promoter.
The classic Jacob-Monod lac operon model illustrates how transcription is regulated in response to metabolic needs.

Step 2: Detailed Explanation:
Let us match each operon component with its specific regulatory or structural role:
- (A) Promoter:
The promoter is a specific sequence of DNA nucleotides upstream of the operon.
It serves as the recognition and binding site for RNA polymerase, which initiates transcription.
Thus, (A) matches with (IV).
- (B) Operator:
The operator is a segment of DNA located between the promoter and the structural genes.
It acts as a molecular switch where a specific repressor protein can bind.
When bound by the repressor, RNA polymerase is physically blocked from transcribing the operon.
Thus, (B) matches with (II).
- (C) Structural gene:
Structural genes are the actual protein-coding sequences in the operon.
They are transcribed into a single polycistronic mRNA that translates into functional enzymes or proteins.
Thus, (C) matches with (III).
- (D) Regulatory gene:
The regulatory gene is located outside the operon unit and is transcribed independently.
It encodes a regulatory protein, such as the repressor protein, which controls operon expression.
Thus, (D) matches with (I).
This pairing results in: (A) - (IV), (B) - (II), (C) - (III), (D) - (I), which matches Option (A).

Step 3: Final Answer:
The correct option is (A).