Question

Mechanism of action of actinomycin D is?

• A. Inhibits DNA dependent RNA synthesis
• B. Activates DNA dependent RNA synthesis
• C. Inhibits RNA dependent DNA synthesis
• D. Activates RNA dependent DNA synthesis

Hint:

It intercalates into DNA and blocks RNA polymerase, halting transcription.

Answer 1

The Correct Option is A

Step 1: Actinomycin D (dactinomycin) is an anticancer antibiotic obtained from microorganisms. This group also includes doxorubicin, daunorubicin, bleomycin, mitomycin and mitoxantrone.

Step 2: Actinomycin D works by intercalating between the two strands of the DNA double helix, specifically binding to guanine-cytosine base pairs. By wedging into the DNA, it interferes with the template function of DNA.

Step 3: This intercalation blocks the movement of RNA polymerase along the DNA, so transcription (DNA-dependent RNA synthesis) is inhibited. Hence the correct answer is that it inhibits DNA-dependent RNA synthesis.

Step 4: It does not activate transcription, nor does it act on RNA-dependent DNA synthesis (reverse transcription), so options b, c and d are wrong. Note that most antitumour antibiotics are cell-cycle non-specific except bleomycin, which acts in the G2 phase.