Tau protein in neurons: defective tau protein = neurofibrillary tangles = alzhei(cid:373)er(cid:859)s. Microfilaments: smallest cytoskeletal element (about 8nm, poly(cid:373)er of the protei(cid:374) (cid:858)acti(cid:374)(cid:859, polypeptide = 42 kda, binds atp, individual molecules = g-actin (globular, polymerized filament = f-actin, several well-characterized functions, maintenance of cell shape, cell movement, cytokinesis, muscle contraction. Filamentous (f)-actin: g-actin monomers have polar structures, monomers are incorporated into the filament in the same orientation, actin filament (f-actin) is polar, (cid:858)plus(cid:859) a(cid:374)d (cid:858)(cid:373)i(cid:374)us(cid:859) e(cid:374)ds. F-actin assembly: globular (g)-actin polymerizes reversibly, nucleation (slow) g-actin dimers and trimmers short filaments, elongation (fast) monomers add to both ends faster at + end, polymerization/de-polymerization and structure/organization of f-actin filaments regulated by actin-binding. 2: head (motor) binds f-actin; generates force, neck- linker / lever arm, tail binds specific cargo. Structure of intermediate filaments: alpha-helical domains wrap around each other forming rope-like dimer, monomers are aligned in parallel; if dimers are polar molecules, 2 dimers associate anti-parallel to make tetramer therefore assembled filaments are.