Extracellular Matrix of the Animal Cell

What is the extracellular matrix (ECM)?

• Something that is made by virtually all multi-cellular organisms.

• Elaborate covering outside animal cell membranes, occupying the space between cells. It is composed of:– Collagen, proteoglycans, and fibronectin, which the

cell secretes.– Different from the plant extracellular matrix, which is

composed of cellulose.• Many ECM components are involved in cell-to-cell

interactions.

Components of the ECM

• Collagen– Most abundant glycoprotein (about half of the total protein in the

body). – Forms strong fibers outside of the cell.

• Fibers are embedded in a network made of proteoglycans.

• Proteoglycans– Collagen fibers are embedded in a network made from

proteoglycans.– Are another class of glycoproteins that consists of a small core

protein with many carbohydrate chains covalently attached. – Large complexes can form when hundreds of proteoglycans

become non-covalently attached to a single long polysaccharide molecule.

Components (cont.)

• Fibronectin– Glycoprotein that attaches the ECM to the cell itself.– Binds to cell surface receptors called integrins, which

are built into the plasma membrane of the cell.• Integrins

– Cell surface receptor that connects to fibronectin, which attaches to the ECM

– Span the membrane and bind on their cytoplasmic side to associated proteins attached to microfilaments of the cytoskeleton.

– Transmit’s changes between the ECM and the cytoskeleton – it integrates changes occurring outside and inside the cell.

Fig. 6-30

EXTRACELLULAR FLUIDCollagen

Fibronectin

Plasmamembrane

Micro-filaments

CYTOPLASM

Integrins

Proteoglycancomplex

Polysaccharidemolecule

Carbo-hydrates

Coreprotein

Proteoglycanmolecule

Proteoglycan complex

ECM Effect on Behavior

• By communicating with a cell through integrins, the ECM can regulate a cell’s behavior.

• ECM can influence the activity of genes in the nucleus. – Speculated that information probably reaches the nucleus by a

combination of chemical and mechanical signaling pathways. • Mechanical includes fibronectin, integrins, and microfilaments of the

cytoskeleton.• The cytoskeleton may then trigger chemical signaling pathways

inside the cell, leading to changes in the proteins being made by the cell and therefore in its function.

• The ECM may help coordinate the behavior of all the cells within that tissue.– Direct connections (intercellular junctions) between cells also

function in this coordination.