cytoskeleton

Microtubules

Hollow tubes with a 25 nm diameter

Microtubules

Tubulin dimers (α-tubulin and β-tubulin)

Microtubules

Cell shape (resist compression), intracellular transport, organelle positioning, chromosome separation (mitotic spindle), flagella and cilia movement

Microtubules

Dynamic instability (grow and shrink); organized from MTOC/centrosome; 9+2 arrangement in cilia and flagella

Microfilaments

Thin solid rods (~7 nm diameter)

Microfilaments

Actin monomers (G-actin polymerizes to F-actin)

Microfilaments

Cell shape (resist tension), cell motility (lamellipodia, filopodia), muscle contraction, cytokinesis (contractile ring in animal cells)

Microfilaments

Highly dynamic; ATP-dependent polymerization; found under plasma membrane (cortical actin)

Intermediate Filaments

Rope-like fibers (~10 nm diameter)

Intermediate Filaments

Various proteins (keratins, lamins, vimentin)

Intermediate Filaments

Mechanical strength, maintain cell shape, anchor nucleus and organelles, nuclear lamina support

Intermediate Filaments

Stable and durable; no motor proteins; tissue-specific; no energy required for polymerization

Microtubules

GTP is used for polymerization

Microfilaments

ATP is used for polymerization

Intermediate Filaments

No energy is required for polymerization

Microtubules

Kinesin (plus-end directed), Dynein (minus-end directed) motor proteins

Microfilaments

Myosin (mostly plus-end directed) motor proteins

Intermediate Filaments

No motor proteins

Microtubules

Intracellular transport, mitotic spindle formation, cilia and flagella movement

Microfilaments

Cell crawling/movement, muscle contraction, cytokinesis

Intermediate Filaments

Mechanical strength, structural stability

Cilia and Flagella

microtubule-based with a 9+2 arrangement

Mitotic Spindle

The mitotic spindle is composed of microtubules, not actin

Cytokinesis

Cytokinesis is driven by actin microfilaments forming the contractile ring

Intermediate Filaments

Intermediate filaments are stable, resist mechanical stress, and do not show dynamic instability