Q.20 Which one of the following statements is a correct description of modes of action of taxol and
colchicine?
(A) Taxol causes DNA damage and colchicine prevents microtubule formation
(B) Taxol stabilizes microtubules and colchicine inhibits protein synthesis
(C) Taxol destabilizes microtubules and colchicine promotes microtubule formation
(D) Taxol stabilizes microtubules and colchicine prevents microtubule formation
The correct answer is option (D): Taxol stabilizes microtubules and colchicine prevents microtubule formation.
Taxol (paclitaxel) binds to polymerized microtubules, suppressing their dynamic instability by preventing depolymerization, which leads to mitotic arrest in cancer cells. Colchicine binds to soluble tubulin dimers, forming a complex that incorporates into microtubule ends and blocks further polymerization.
Option Analysis
Option (A) states Taxol causes DNA damage and colchicine prevents microtubule formation. Taxol targets microtubules, not DNA directly, making this incorrect despite colchicine’s effect being accurate.
Option (B) claims Taxol stabilizes microtubules and colchicine inhibits protein synthesis. Taxol’s action is correct, but colchicine acts on tubulin polymerization, not translation or transcription.
Option (C) suggests Taxol destabilizes microtubules and colchicine promotes microtubule formation. This reverses both mechanisms: Taxol stabilizes while colchicine depolymerizes or prevents assembly.
Option (D) accurately describes Taxol stabilizing microtubules against disassembly and colchicine inhibiting their formation by tubulin binding.
Taxol and Colchicine: Modes of Action on Microtubules
Taxol and colchicine represent classic microtubule-targeting agents with opposing effects central to cell biology and cancer therapy. These drugs disrupt mitotic spindle function by altering microtubule dynamics, essential for chromosome segregation.
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Taxol binds β-tubulin in assembled microtubules, reducing protofilaments and enhancing stability against cold or calcium-induced disassembly.
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Colchicine forms irreversible tubulin complexes that cap growing ends, halting polymerization at low doses and causing depolymerization at high doses.
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Both induce metaphase arrest but via distinct sites: taxol on polymers, colchicine on dimers.
| Drug | Binding Target | Primary Effect | Cellular Outcome |
|---|---|---|---|
| Taxol | Polymerized microtubules (β-tubulin) | Stabilizes, suppresses dynamic instability | Bundled microtubules, mitotic arrest |
| Colchicine | Free tubulin dimers | Prevents polymerization, promotes depolymerization | Spindle disruption, no microtubule elongation |
This contrast makes them valuable in exams like CSIR NET Life Sciences, testing comprehension of cytoskeletal pharmacology.
