Q.1 Which one of the following compounds inhibits the polymerization of tubulin to
microtubules in animal cells?
(A) ATP
(B) Taxol
(C) Thymosin
(D) Vinblastine
Vinblastine inhibits tubulin polymerization to microtubules in animal cells. This compound, a vinca alkaloid used in chemotherapy, binds to tubulin and prevents its assembly into microtubules, disrupting mitosis.
Option Analysis
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(A) ATP: Adenosine triphosphate supports microtubule assembly by aiding tubulin ring formation as nucleation centers and enhancing polymerization rates when combined with GTP.
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(B) Taxol: Taxol (paclitaxel) stabilizes microtubules by promoting tubulin polymerization, reducing dynamic instability, and making polymers resistant to depolymerization.
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(C) Thymosin: Thymosin β4 sequesters actin monomers, inhibiting actin polymerization, but has no role in tubulin or microtubule dynamics.
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(D) Vinblastine: Vinblastine binds tubulin at low concentrations, suppressing microtubule growth, shortening, and dynamic instability without net depolymerization initially, effectively inhibiting polymerization.
Microtubules form from α/β-tubulin dimers polymerizing in cells, crucial for mitosis, intracellular transport, and structure. Inhibitors disrupting this process target cancer by halting cell division. For CSIR NET Life Sciences aspirants, understanding which compound inhibits tubulin polymerization to microtubules is key in cell biology sections.
Microtubule Dynamics Basics
Tubulin polymerization requires GTP hydrolysis and dynamic instability—growth, shortening, pauses. Drugs bind tubulin to either stabilize (promote assembly) or destabilize (inhibit polymerization). Vinca alkaloids like vinblastine cap microtubule ends, reducing catastrophe frequency and dynamicity by 75% at low nanomolar levels.
Why Vinblastine Inhibits Polymerization
Vinblastine binds high-affinity sites on β-tubulin, blocking dimer addition to microtubule ends. At 3-64 nM, it suppresses growth/shrinkage rates in living cells without immediate depolymerization, leading to mitotic arrest. This makes it the correct choice over stabilizers or unrelated molecules.
| Compound | Effect on Tubulin Polymerization | CSIR NET Relevance |
|---|---|---|
| ATP | Promotes via nucleation | Energy source, not inhibitor |
| Taxol | Enhances stability/assembly | Stabilizer, opposite effect |
| Thymosin | No effect (actin-specific) | Actin sequestration |
| Vinblastine | Inhibits assembly/dynamics | Correct: Blocks microtubule formation |
Exam Tips for CSIR NET
Compare vinblastine (depolymerizer) with Taxol (stabilizer) in MCQs. Both cause G2/M arrest but via opposite mechanisms—vinblastine prevents spindle formation. Practice with similar questions on colchicine site binders.
