BIO 201 Chapter 4: Cell Junctions

Cell junctions

contact points between plasma membranes of adjacent tissue cells

Tight junctions

• Consists of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells

• Prevents contents of organs from leaking into blood or surrounding tissue

• Ex. lining of intestines, stomach, bladder

Adhering junctions

• Contain plaque which attaches to membrane proteins and microfilaments of the cytoskeleton

• Help prevent epithelial surfaces from separating during contractile activities, involved in dynamic cell interactions

• Ex. food moving through intestines

Cadherin

transmembrane glycoproteins that insert into plaque from opposite the plasma membrane, connecting to cadherins of the adjacent cell; along with microfilaments (actin filaments), forms adhesion belt

Desmosomes

• Contain plaque and cadherins; however, they instead connect to intermediate filaments

• Spot weld-like junctions

• Prevent epithelial cells from separating under tension and cardiac cells separating during contraction

Hemidesmosomes

• Integrins attach to intermediate filaments made of keratin

• Anchor cells not to each other but to basement membrane

Gap junctions

• Connexin proteins form tunnels (connexons) that connect neighboring cells

• Allow diffusion of ions (nutrients) from cytosol of one cell to another

• Ex. developing embryo, nerve communication with contractile muscles