Eukaryotes have two major chromatin proteins in SMC family: Cohesins and Condensin. These Structural Maintenance of Chromosome (SMC) complexes—cohesin (SMC1/SMC3) and condensin (SMC2/SMC4)—organize mitotic chromosomes by holding sister chromatids together and compacting chromatin axes, respectively.​

Option Analysis

• (1) Integrin and laminin: Transmembrane adhesion receptors and extracellular matrix glycoproteins; unrelated to chromatin or SMC family.

• (2) Cohesins and condensin: Correct—Cohesin establishes sister chromatid cohesion from S-phase through anaphase; condensin drives mitotic chromosome condensation via loop extrusion.

• (3) Hemoglobin and myoglobin: Oxygen-transport/storage proteins in blood/muscle; no chromosomal function.

• (4) Actin and myosin: Cytoskeletal motor proteins for contraction/cytokinesis; not chromatin-associated SMC complexes.

Answer: (2) Cohesins and condensin.​

Introduction to SMC Chromatin Proteins

Eukaryotes have two major chromatin proteins in SMC family: cohesins and condensins. These ATP-powered ring complexes containing SMC heterodimers (SMC1/3, SMC2/4) orchestrate chromosome segregation and compaction during mitosis.​

Cohesin Complex Functions

SMC1α/SMC3 forms kleisin-ring with SCC1, embracing sister chromatids post-replication. Cleaved by separase at anaphase onset; Eco1 acetylates SMC3 for cohesion establishment.

Condensin Complex Role

SMC2/SMC4 with kleisin CAP-H compacts chromatin 10,000-fold via ATPase-driven loop extrusion. Essential for resolving catenanes, spindle assembly checkpoint satisfaction.​

Why Other Options Are Incorrect

Integrins/laminins mediate ECM signaling; hemoglobin/myoglobin bind O2; actin/myosin drive cytokinesis—none belong to SMC superfamily of chromosomal ATPases.​

GATE Cell Biology Relevance

Tests SMC nomenclature: cohesin (cohesion), condensin (condensation). Critical for mitosis/meiosis, aneuploidy, cancer biology questions.​