Q.101 Which of the following statements is/are TRUE for Colchicine?
(A) It binds to tubulin molecule and disrupts the assembly/polymerization of
microtubule.
(B) It inhibits crossover of chromosomes during meiosis.
(C) It inhibits chromosome condensation during Prophase.
(D) It blocks mitotic cells in Metaphase.
Colchicine blocks mitotic cells in metaphase by disrupting microtubule assembly. Options (A) and (D) are true, while (B) and (C) are false.
Option Analysis
Option (A): Colchicine binds to soluble tubulin dimers, forming complexes that prevent microtubule polymerization and disrupt spindle formation. This interference halts microtubule assembly critical for mitosis.
Option (B): Colchicine does not specifically inhibit chromosome crossover during meiosis. While it disrupts microtubule-dependent processes like telomere clustering or synapsis in some studies, crossover formation occurs earlier via recombination proteins, not directly targeted by colchicine.
Option (C): Colchicine fails to inhibit chromosome condensation in prophase. Condensation relies on condensins and histone modifications, not microtubules, so colchicine-arrested cells show highly condensed metaphase chromosomes.
Option (D): Colchicine arrests mitotic cells at metaphase by preventing spindle elongation, stopping chromosomes from moving to anaphase. Cells accumulate as “c-metaphases” unable to proceed.
Correct Answer
(A) and (D) are TRUE. This matches CSIR NET-level expectations for colchicine’s anti-mitotic action on tubulin and metaphase arrest.
Introduction to Colchicine’s Action
Colchicine blocks mitotic cells in metaphase through precise binding to tubulin, preventing microtubule assembly essential for spindle function. Derived from autumn crocus, this alkaloid serves as a classic mitotic poison in research and therapy. For CSIR NET aspirants, mastering colchicine’s effects on cell division proves crucial.
Microtubule Binding and Polymerization Inhibition
Colchicine forms irreversible complexes with tubulin heterodimers, blocking their addition to microtubule ends. This disrupts dynamic instability, halting spindle formation needed for chromosome alignment. Low doses stop growth; high doses cause depolymerization.
Mitotic Arrest at Metaphase
Cells treated with colchicine progress through prophase but stall at metaphase, forming scattered metaphase chromosomes without spindles. This “metaphase arrest” enables chromosome doubling in polyploidy studies. No impact occurs on anaphase or telophase progression.
Effects on Meiosis and Other Processes
Colchicine indirectly affects meiosis via microtubule disruption but spares crossover formation, which precedes spindle needs. Chromosome condensation in prophase remains unaffected, as it depends on non-microtubule mechanisms.
Applications in Research and CSIR NET
Researchers use colchicine to induce polyploids and study mitosis. CSIR NET questions test its metaphase block and tubulin binding, distinguishing from meiosis or prophase effects.
