Cell Junctions, Cell Adhesion, and the Extracellular Matrix

Lignin

A complex network of phenolic complounds that is an abundant polymer in secondary cell walls.

Cadherin

A member of a family of proteins that mediate Ca2+ dependant cell-cell adhesion in animal tissues

Adherens Junction

Anchoring Junction that connects actin filaments in the one cell to those in the next cell.

Adhesion belt

Belt like anchoring junction that encircles the apical end of an epithelial cell and attaches it to the adjoining cell.

Cellulose microbibril

Bundle of about 40, long linear chains of covalently linked glucose residues all witht he same polarity, organized in an overlapping parallel array.

Fibroblast

Common cell type in connective tissue that secretes an extracellular matrix rich in collagen and other extracellular matrix macromolecules.

Plasmodesmata

Communicating cell-cell junctions in plants in which a channel of cytoplasm lined by plasma membrane connects two adjacent cells through a small pore in their cell walls

Extracellular Matrix

Complex network of polysaccharides and proteins secreted by cells that serves as a structural element in tissues and also influences tissue development and physiology.

Focal Adhesion Kinase

Cytoplasmic tyrosine kinase present at cell-matrix junctions in association with the cytoplasmic tails of integrins.

Anchorage Dependence

Dependence of cell growth on attachment to a substratum.

Polarized

Describes a structural property of epithelial sheets and their individual cells, which have on surface attached to the basal lamina below and the opposite surface exposed to the medium above.

Apical

Describes the tip of a cell. For an epithelial cell, it is the exposed free surface opposite to the surface attached to the basal lamina.

Laminin-1

Extracellular matrix protein found in basal laminae, where it forms a sheet like network.

Fibronectin

Extracellular matrix protein that binds to cell-surface integrins to promote adhesion of cells to the matrix and to provide guidance to migrating cells during embryogenisis.

Collagen

Fibrous protein rich in glycine and proline that, in its many forms, is a major component of the extracellular matrix and connective tissues.

Glycosaminoglycan (GAG)

General name for long, linear, highly charged polysaccharides composed of a repeating pair of sugars, on of which is always an amino sugar, that is found covalently linked to a protein core in the extracellular matrix

Elastin

Hydrophobic protein that forms extracellular extensible fibers that give tissues their stretchability and resilience

Homophilic

Like-to-like protein interactions in which a molecule on one cell binds to an identical, or closely related, molecule on an adjacent cell

Septate Junction

Main type of occluding junction in invertebrates; it seals the adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other.

Tight Junction

Main type of occluding junction in vertabrates; it seals adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other.

Selectin

Member of a family of cell-surface carbohydrate-binding proteins that mediate transient, Ca2+-dependent cell-cell adhesion in the bloodstream, for example, between white blood cells and the endothelium of the blood vessel wall.

Integrin

Member of a large family of transmembrane proteins involved in the adhesion of cells to the extracellular matrix and to each other.

Integrin

Principle receptor on animal cells for binding most extracellular matrix proteins, including collagens, fibronectin, and laminins.

Secondary Cell Wall

Rigid cell covering laid down in layers inside the initial covering once cell growth has stopped.

Turgor Pressure

The large internal hydrostatic pressure that develops in plant cells due to the osmotic imbalance between the cell interior and the fluid in the plant cell wall.

Primary Cell Wall

Thin and extensible cell covering on new plant cells that can accommodate their growth

Basal Lamina (basement membrane)

Thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from connective tissue.

Desmosome Junction

Type of anchoring junction, usually formed between two epithelial cells, characterized by dense plaques of protein into which the intermediate filaments in the two adjoining cell insert.

Fibrillar collagen

Type of collagen molecule that assembles into ropelike structures and larger cablelike bundles.

Connexon

Water-filled pore in the plasma membrane formed by a ring of six protein subunits, which link to an identical assembly in an adjoining cell to form a continuous channel between the two cells.