Cell Junctions
Junctional Complex
3 part structure consisting of tight junction (zonula occludens), adherens junction (zonula adherens), and a desmosome (macula adherens). Formed between epithelial cells near the apical surface of most simple epithelia.
Three major types of cell junctions:
Occluding junctions, attachment junctions, and communication junctions.
Hemidesmosome
They look like only have of a desmosome. Anchor the intermediate filaments of the cell's cytoskeleton to laminin in the underlying basal lamina or basement membrane. Common in epithelia that are subject to high mechanical shearing forces such as trachea, esophagus, etc.
Attachment Junctions Function and Mechanism
To bind adjacent epithelial cells together. They are found on both the lateral and the basal surfaces of epithelial cells
Tight Junctions (Occluding Junctions) Function and Mechanism:
To prevent molecules and particles on one side of an epithelial sheet from seeping between cells to reach the other side of the epithelium. Occludin in one cell spans the plasma membrane and links to occludin from the adjacent cell. Occludin arises form a transmembrane protein. They also aid as permeability barriers and maintain epithelial cell polarity.
Communicating Junctions
to permit passage of electrical signals, chemical signals, and metabolites between adjacent cells
Two types of attachment junctions:
-Those associated with actin filaments -Those associated with intermediate filaments (desmosomes and hemi-desmosomes)
Adherens Junction
Band-like adhering junction. Zonula adherens extends around the cell adjacent to the tight junction to which it gives structural support. Linker protein is E-cadherin- attach via a series of small proteins to actin filaments in the cytoskeleton.
Gap Junction
Communication Junction- tube like structure called a connexon. Composed of proteins called connexins. Permits the direct passage of ions and molecules between the cytoplasm of one cell and that of its neighbor.
Desmosome
Spot attachment-cytoskeletal filaments are intermediate filaments composed of keratin
