Eukaryotic Cell Cytoskeleton and Intercellular Junctions

Vocabulary flashcards covering major cytoskeletal components, cilia/flagella, ECM, plant cell walls, and intercellular junctions described in the notes.

Microtubules

Hollow tubes (\sim 25 \text{ nm} diameter) made of α- and β-tubulin protofilaments, crucial for cell shape, organelle movement, chromosome segregation, and the structure of cilia/flagella.

Protofilaments

Linear chains of tubulin dimers that assemble to form a microtubule.

Centrosome

The microtubule-organizing center near the nucleus; in animal cells it contains a pair of centrioles and is a major site of microtubule nucleation.

Centriole

One of a pair of cylindrical structures in the centrosome, each with nine triplets of microtubules arranged in a ring.

Spindle apparatus

Microtubule-based structure formed during cell division that organizes and segregates chromosomes

MTOC (microtubule-organizing center)

Sites in the cell where microtubules nucleate and are organized; examples include the centrosome and other cellular locations.

Cilia

Membrane-bound, slender projections extending from a cell; can be non-motile (sensory) or motile; core structure driven by microtubules with a typical 9+2 arrangement in motile cilia.

Flagella

Longer cellular projections used for locomotion; have a similar microtubule-based core to cilia and typically beat with a different motion; commonly found on sperm.

Basal body

A structure that anchors a cilium or flagellum to the cell; derived from a centriole.

9+2 arrangement

Ultrastructure of motile cilia/flagella: nine outer doublets of microtubules surrounding a central pair.

9+0 arrangement

Ultrastructure of a primary (non-motile) cilium: lacks the central pair of microtubules.

Dynein

Motor protein that drives bending movements of cilia and flagella by causing sliding between microtubule doublets.

Kinesin

Motor protein that moves along microtubules (usually toward the plus end) and mediates intracellular transport.

Actin

Globular actin (G-actin) monomers polymerize into filamentous actin (F-actin), forming two intertwined strands; diameter ~7 nm.

Microfilaments

Actin filaments (F-actin) built as a twisted double chain of actin subunits; ~7 nm in diameter; support cell shape, enable movement, participate in muscle contraction and cytokinesis, and drive cytoplasmic streaming.

G-actin

Globular actin monomer that polymerizes to form F-actin.

F-actin

Filamentous actin; polymerized form of actin making up microfilaments, ~7 nm in diameter.

Myosin

Motor protein that interacts with actin to cause muscle contraction and other cellular movements.

Cytoplasmic streaming

Circular flow of cytoplasm within cells, propelled by actin–myosin interactions, aiding distribution of materials.

Muscle contraction

Contraction results from the interaction between actin and myosin filaments sliding past one another.

Intermediate filaments

Fibrous keratin-family proteins 8–12 nm in diameter that provide mechanical strength, anchor the nucleus, and form the nuclear lamina.

Keratin

Protein subunits of intermediate filaments, diverse by cell type.

Nuclear lamina

A meshwork of intermediate filaments lining the inner surface of the nuclear envelope, providing structural support.

Extracellular matrix (ECM)

Glycoproteins and other macromolecules outside animal cells that provide support, adhesion, movement, and regulation; major components include collagen, fibronectin, and integrins that link to the cytoskeleton.

Collagen

Primary structural protein of the ECM, forming fibrous networks that provide tensile strength.

Fibronectin

ECM glycoprotein that binds to integrins and other ECM components to promote adhesion.

Integrin

Transmembrane receptors that connect the ECM to the cytoskeleton and mediate adhesion and signaling.

Cell wall

Extracellular structure in plants that protects the cell, maintains shape, and limits water uptake; composed mainly of cellulose; may have primary, middle lamella, and secondary layers.

Primary cell wall

Thin, flexible outer wall formed during cell growth.

Middle lamella

Thin layer rich in pectin between primary walls of adjacent plant cells, helping glue cells together.

Secondary cell wall

Additional rigid layer laid between the plasma membrane and the primary cell wall in some cells for extra strength.

Plasmodesmata

Membrane-lined channels that connect plant cells, enabling transport of ions, hormones, and metabolites; establish the symplast (shared cytoplasm).

Symplast

Continued cytoplasm of connected plant cells via plasmodesmata, allowing intercellular transport.

Tight junctions

Junctions that seal neighboring cells at the apical region to prevent leakage of extracellular fluid; involve transmembrane proteins like claudins and JAMs, connected to the actin cytoskeleton by ZO proteins.

Desmosomes

Anchoring junctions that fasten cells together into strong sheets; composed of desmoglein and desmocollin cadherins linked to intermediate filaments via plakins and catenins.

Gap junctions

Intercellular channels formed by connexins that allow passage of small molecules and ions between adjacent cells.

Intercellular junctions

Connections between cells that include tight junctions, desmosomes, and gap junctions, linking membranes to the cytoskeleton.