Question:
Which of the following antibiotic specifically inhibits the initiation of transcription in prokaryotes?
(A) Rifampicin
(B) Azithromycin
(C) Rifamycin B
(D) Cordycepin
Choose the correct answer from the options given below:
Which of the following antibiotic specifically inhibits the initiation of transcription in prokaryotes?
(A) Rifampicin
(B) Azithromycin
(C) Rifamycin B
(D) Cordycepin
Choose the correct answer from the options given below:
(A) Rifampicin
(B) Azithromycin
(C) Rifamycin B
(D) Cordycepin
Choose the correct answer from the options given below:
Show Hint
The Rifamycin class of antibiotics (including Rifampicin and Rifamycin B) are highly effective against *Mycobacterium tuberculosis* because they block bacterial RNA polymerase at the very beginning of transcription.
Updated On: Jul 21, 2026
- (A) and (D) only.
- (B) and (D) only.
- (A) and (B) only.
- (A) and (C) only.
Show Solution
Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Many antibiotics act by selectively inhibiting bacterial transcription or translation pathways, exploiting structural differences between prokaryotic and eukaryotic machinery.
Detailed Explanation:
Let us analyze the mechanisms of action for the listed drugs:
- (A) Rifampicin: This is a semisynthetic bactericidal antibiotic that binds specifically to the $\beta$ subunit of bacterial RNA polymerase.
By binding near the active site, it physically blocks the path of the newly synthesized nascent RNA chain after the formation of the first 2 to 3 phosphodiester bonds, thereby preventing transcription initiation. Thus, (A) is correct.
- (C) Rifamycin B: This is the natural parent compound of rifampicin.
Like rifampicin, it specifically binds to bacterial RNA polymerase to prevent the initiation of transcription. Thus, (C) is correct.
- (B) Azithromycin: This is a macrolide antibiotic that inhibits bacterial translation (protein synthesis) by binding to the 50S ribosomal subunit. It does not inhibit transcription.
- (D) Cordycepin (3'-deoxyadenosine): This is a nucleoside analog that lacks a 3'-hydroxyl group.
It is incorporated into growing RNA chains, causing premature chain termination of eukaryotic transcription and polyadenylation. It does not specifically target prokaryotic transcription initiation.
Therefore, the antibiotics that specifically inhibit prokaryotic transcription initiation are Rifampicin and Rifamycin B.
Step 2: Final Answer:
The correct option is (D), representing (A) and (C) only.
Many antibiotics act by selectively inhibiting bacterial transcription or translation pathways, exploiting structural differences between prokaryotic and eukaryotic machinery.
Detailed Explanation:
Let us analyze the mechanisms of action for the listed drugs:
- (A) Rifampicin: This is a semisynthetic bactericidal antibiotic that binds specifically to the $\beta$ subunit of bacterial RNA polymerase.
By binding near the active site, it physically blocks the path of the newly synthesized nascent RNA chain after the formation of the first 2 to 3 phosphodiester bonds, thereby preventing transcription initiation. Thus, (A) is correct.
- (C) Rifamycin B: This is the natural parent compound of rifampicin.
Like rifampicin, it specifically binds to bacterial RNA polymerase to prevent the initiation of transcription. Thus, (C) is correct.
- (B) Azithromycin: This is a macrolide antibiotic that inhibits bacterial translation (protein synthesis) by binding to the 50S ribosomal subunit. It does not inhibit transcription.
- (D) Cordycepin (3'-deoxyadenosine): This is a nucleoside analog that lacks a 3'-hydroxyl group.
It is incorporated into growing RNA chains, causing premature chain termination of eukaryotic transcription and polyadenylation. It does not specifically target prokaryotic transcription initiation.
Therefore, the antibiotics that specifically inhibit prokaryotic transcription initiation are Rifampicin and Rifamycin B.
Step 2: Final Answer:
The correct option is (D), representing (A) and (C) only.
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