Practice question

Intermediate filaments constitute one of three major cytoskeletal polymers alongside actin microfilaments and microtubules, classified by ten nanometer diameter and apolar rope-like assembly through parallel coiled-coil dimers antiparallel tetramers laterally associating into filaments without polarity. Major classes include keratins in epithelia, vimentin in mesenchyme, desmin in muscle, glial fibrillary acidic protein in astrocytes, neurofilaments in neurons, lamins in nucleus. Their primary mechanical role is tensile resistance to shear and stretching, absorbing deformation through flexible networks anchored at cell-cell desmosomes and cell-matrix hemidesmosomes linked by plectin and desmoplakin. This protects tissues experiencing repetitive strain, as seen in blistering diseases upon keratin mutation. They do not generate ATP, actively transport vesicles, or directly regulate microtubule growth, though they cross-talk via plectin. Knockout studies show fragility rather than motility defects, indicating specialization toward structural support enabling tissue cohesion, nuclear scaffolding for chromatin organization and integration of mechanical signals over long timescales beyond dynamic actin and microtubule remodeling.