Actin, microtubules, intermediate filaments, molecular motors, dynamic instability.
Cytoskeleton And Motility
Cytoskeleton
Dynamic intracellular polymer network providing shape, polarity, transport, division. Three systems: actin (7 nm), intermediate filaments…
Actin filament (F-actin)
Double-helical polar polymer of G-actin monomers (~42 kDa). ATP-actin adds at barbed end; ADP-actin dissociates at pointed end —…
Microtubule
Hollow tube (25 nm OD) of 13 α/β-tubulin protofilaments. Nucleated at γ-TuRC (centrosome, basal body). GTP-cap drives dynamic instability;…
Dynamic instability
Mitchison-Kirschner 1984: microtubules stochastically switch between growth (rescue) and shrinkage (catastrophe) at plus ends. GTP-cap…
Intermediate filament
Mechanically resilient (tensile-stress bearing) 10 nm fibres of tissue-specific proteins: keratin (epithelia), vimentin (mesenchyme),…
Myosin
Actin-based ATPase motor family (>35 classes in humans). Myosin II drives muscle contraction + cytokinesis; myosin V/VI do organelle…
Kinesin
Plus-end-directed microtubule motor (mostly). ~45 human kinesins (KIF1-KIF27). Two heads walk hand-over-hand with 8 nm step per ATP,…
Dynein
Minus-end-directed microtubule motor. Cytoplasmic dynein does organelle transport + spindle positioning; axonemal dynein powers…
Cell migration
Protrusion (actin polymerisation) → adhesion (integrins) → contraction (actomyosin) → retraction. Arp2/3 drives lamellipodia, formins drive…
Mitotic spindle
Bipolar microtubule structure driving chromosome segregation. Kinetochore-MT attachment, spindle checkpoints, anaphase A (MT shortening)…
Actin polymerization treadmilling kinetics
Polar actin filaments grow at the (+) barbed end and shrink at the (-) pointed end at steady state when [G-actin] lies between the two…
Molecular motor asymmetric stepping
Kinesin/dynein/myosin take ATP-driven 8-36 nm steps with forward/backward bias set by load force F via p_+/p_- = exp(-Fd/k_BT); mean…
Actin treadmilling (Pollard)
Wegner 1976 + Pollard 1986 G-actin / F-actin polymerization: critical-concentration C_c at + barbed end < C_c at - pointed end; net + end…
Microtubule search-and-capture
Holy-Leibler 1994 + Kirschner-Mitchison 1986: dynamic-instability with Pcatastrophe + Prescue rates; chromosome capture stochastic + biased…
Kinesin step mechanism
Svoboda-Block 1994 + Asbury-Fehr 2003: kinesin-1 hand-over-hand 8 nm steps; ATP hydrolysis coupled to processive movement; Yildiz-Selvin…
Myosin cross-bridge cycle (Huxley 1957)
A F Huxley 1957 sliding-filament + cross-bridge cycle: ATP-bind detaches; M+ATP+actin binding then power-stroke; force-velocity hyperbola…
Axonemal dynein (cilia + flagella)
Gibbons 1965 dynein discovery; 9+2 axoneme; Sale-Satir 1977 sliding-doublet-microtubule + dynein-arm walking; primary-cilia +…
Intermediate filaments (keratin/vimentin)
Steinert-Roop 1988 + Fuchs-Cleveland 1998: 6 IF classes (keratin/vimentin/desmin/neurofilament/lamin/nestin); 10 nm coiled-coil dimer +…
Actin (Straub 1942)
F Straub 1942 + Wertheim-Pollard actin-purification; modern G-F polymerization + Lodish-Pollard-Borisy 2003 Arp2/3 nucleation.
Microtubule (Borisy 1967)
G Borisy 1967 + Inoue 1981 dynamic-instability; modern + Mitchison-Kirschner 1984 tau-bound + GTP-cap regulation.
Kinesin (Vale 1985)
R Vale 1985 + Brady kinesin-organelle-transport; modern processivity + step-size 8nm + 2024 single-molecule imaging.
Dynein (Gibbons 1965)
I Gibbons 1965 axoneme-dynein; modern flagellar-beat + 9+2 axoneme + ciliopathy + cytoplasmic-dynein-1 cargo transport.
IF (Lazarides 1980)
E Lazarides 1980 intermediate-filament; modern keratin + lamin + EB-rosette + Werner-progeria + skin-disease epidermolysis-bullosa.
Septin (Hartwell 1971)
L Hartwell 1971 (Nobel 2001) septin-yeast-CDC; modern higher-order-filaments + cytokinesis + diffusion-barrier neuron synapse.