BIO 101 7c: Cytoskeleton

Cytoskeleton

A dense and complex network of three protein polymers that regulates cell shape, structural stability, organelle movement, and whole-cell locomotion.

Structural Polarity

Having directionally distinct ends (plus and minus ends), which allows directional growth and specific motor protein tracking.

Actin Filaments (Microfilaments)

The thinnest cytoskeletal polymer (7 nm), consisting of two intertwined strands of G-actin monomers that maintain cell shape by resisting tension.

Myosin

A motor protein that interacts with actin filaments, using ATP hydrolysis to drive muscle contraction, cytokinesis, and cytoplasmic streaming.

Cytoplasmic Streaming

An actin-myosin driven movement in plant cells that circulates cytoplasm and organelles around the central vacuole.

Intermediate Filaments (IFs)

Medium-sized polymers (8–12 nm) made of overlapping coiled-coil dimers (like keratins or lamins) that lack polarity and provide high mechanical strength.

Nuclear Lamins

A specialized meshwork of intermediate filaments that lines and structurally supports the inner nuclear envelope.

Progeria

A genetic disease caused by a mutation in a nuclear lamin gene, resulting in premature cellular aging and structural collapse of the nucleus

Microtubules

The largest cytoskeletal element (25 nm), forms hollow tubes composed of alpha- and beta-tubulin heterodimers that resist compression of the cell.

Centrosome

The primary microtubule-organizing center (MTOC) in animal cells, contains two centrioles and anchors the minus ends of microtubules.

Dynamic Instability

A microtubule behavior characterized by alternating periods of rapid growth (via a GTP cap) and sudden shrinking, known as catastrophe.

Kinesin

A motor protein dimer that hydrolyzes ATP to "walk" transport vesicles toward the plus end of a microtubule track.

Axoneme

The structural core of eukaryotic cilia and flagella consists of a characteristic "9 + 2" arrangement of microtubule doublets.

Dynein

A motor protein with side arms that "walk" toward the minus end of adjacent microtubule doublets, causing the axoneme to bend and drive cell motility.