Tight Junctions

• Occluding junctions • Sealing strands are rows of

transmembrane proteins

Transcellular Transport

• Essential for segregating transport proteins

Anchoring Junctions

• Attach cytoskeleton to neighboring cell or to extracellular matrix

• Intracellular anchor proteins

• Transmembrane adhesion proteins

Adherens Junctions

• Connect actin filaments in neighboring cells

• Cadherin transmembrane adhesion proteins

• Catenin anchor proteins

Desmosomes

• Connect intermediate filaments in neighboring cells• Cadherin transmembrane adhesion proteins• Complex of anchoring proteins• Pemphigus autoimmune disease

Focal Adhesions

• Connect actin filaments to extracellular matrix

• Integrin transmembrane adhesion proteins

• Various anchor proteins

Hemidesmosomes

• Connect intermediate filaments to basal lamina

• Integrin transmembrane adhesion proteins

• Plectin anchor protein

Types Of Anchoring Junctions Junction Transmembrane Extracellular Cytoskeletal Intracellular

Adhesion Protein Attachment Attachment AnchorProtein

Cell-CellAdherens cadherins cadherin actin filaments cateninsJunction (E-cadherin) (- and -)

Desmosome cadherins cadherin intermediate catenins,(desmoglein, desmocollin) filaments desmoplakin

Cell-MatirxFocal integrins extracellular actin filaments talin, vinculin,adhesion matrix proteins others

Hemi- integrin 64 extracellular intermediate plectindesmosome matrix proteins filaments

Gap Junctions

• Communicating junctions• Channels composed of connexin

transmembrane proteins

Junctional Complex

• Same relative positions of three junctions in most epithelium

Glycosaminoglycans

• Unbranched polysaccharide chain with repeating disaccharide unit

• Large volume, high negative charge result in gel-like form

Hyaluronan

• Simple GAG• Not usually linked to protein

• Most GAGs covalently attached to protein• Synthesized in Golgi apparatus• Link tetrasaccharide added to serine; other

sugars added one at a time

Proteoglycans

Diversity Of Proteoglycans

• Extensive variation in types and number of GAG chains

Collagens

• Multiple chains associate in different combinations

oProline- ring, stabilizes helixoGlycine- small, tight chain packing

• Triple helix from three collagen chains• Rich in proline and glycine

• Synthesized as pro--chain precursors• Cleavage of pro-peptides following secretion• Self-assembly into fibrils and aggregation into fibers

Synthesis of Collagens

Hydroxylation In Collagen

• Certain lysine and proline residues• Form interchain hyrodrogen bonds• Requires vitamin C; deficiency results

in easy bruising, petechiae, scurvy

Cross-Linking Of Collagen

• Occurs between lysine residues of separate molecules to strengthen fibrils

Genetic Diseases Affecting Collagen

AffectedDisease Collagen Mutant Phenotype

Osteogenesis imperfecta I weak bones, fractures

Chondrodysplasias II cartilage deficiency

Ehlers-Danlos syndrome III fragile skin & blood vessels, loose joints

Elastin

• Elastin molecules are cross-linked• Molecules in network expand and contract

Fibronectin

• Multiple binding sites for extracellular matrix and cell surface molecules

Laminin

• Component of basal lamina• Composed of , , and chains that form distinct isoforms

Basal Lamina

• Sheet-like networks of laminin and type IV collagen