Q.33 Proteins responsible for structural maintenance of chromosomes are
- Condensin
- Cohesin
- Collagen
- Both 1 and 2
Both condensin and cohesin are proteins responsible for structural maintenance of chromosomes, while collagen is not. The correct answer is option 4: Both 1 and 2.
Introduction
Proteins structural maintenance chromosomes condensin cohesin are essential SMC complexes regulating chromosome architecture during cell division. This guide analyzes all MCQ options, explains condensin (compaction) vs. cohesin (sister chromatid cohesion), and clarifies why collagen doesn’t belong for exam success.
Key Proteins Defined
Condensin: Multi-subunit SMC complex (SMC2/SMC4 core) compacts chromatin into organized mitotic/meiotic chromosomes by forming intra-chromatid loops. Active from prophase; condensin I post-NEBD, condensin II earlier.
Cohesin: SMC3/SMC1 complex holds sister chromatids together from S-phase through metaphase I (meiosis) or metaphase (mitosis). Enables proper bipolar attachment; cleaved by separase at anaphase.
Both maintain chromosome structure: condensin shortens axes, cohesin resists spindle forces.
Option Analysis
Option Protein(s) Responsible for Chromosome Structure? Explanation 1 Condensin Yes Compacts DNA into loops; essential for mitotic chromosome formation and segregation. Mutations cause aneuploidy. 2 Cohesin Yes Mediates sister chromatid cohesion; maintains bipolar orientation under spindle tension. 3 Collagen No Extracellular matrix protein (triple helix); forms connective tissue, not nuclear chromosome scaffold. 4 Both 1 and 2 Yes Correct: Both SMC complexes geometrically partition (condensin axial, cohesin radial) for full structural integrity. Functional Comparison
Feature Condensin Cohesin Primary Role Chromosome compaction Sister chromatid cohesion DNA Interaction Intramolecular cross-links (loops) Intermolecular (sister tethering) Mitotic Timing Prophase onward S-phase to anaphase Localization Chromosome axes Pericentric/radial chromatin Structure Closed hinge conformation Open hinge Meiosis Context: Both enriched pericentromerically; condensin prevents stretching, cohesin limits loop excursion under spindle force. Critical for NEET-level mitosis/meiosis questions.
