The extracellular matrix (ECM) is a complex structure primarily made of macromolecules such as proteins and carbohydrates that provide support to tissues. Collagen is the most abundant structural protein within the ECM, with various types serving different functions, including the formation of basal laminae and linking cells to underlying connective tissues. Additionally, glycosaminoglycans and proteoglycans contribute to the ECM's mechanical properties, while adhesion proteins like fibronectin and laminin facilitate connections between the ECM components and cells.

1. EXTRA CELLULAR MATRIX
Adarsh P P

2. TISSUES
• Not solely made of cells
• Most of their volume is
• Matrix is composed of
macromolecules (Proteins and
Carbohydrates)
• They are secreted locally by cells and
organized into a meshwork in close
associations with the cells.
Main Class Of Macromolecules:

3. MATRIX STRUCTUAL PROTEINS
• Extracellular matrix is composed of tough fibrous proteins
embedded in a gel like polysaccharide substance.
• It also contain adhesion proteins, that helps in linkage.
• Major structural protein is COLLAGEN. They are large family
of 27 different members.

4. • The triple helix domains of the collagen consist of repeats of
the amino acid sequence Gly-X-Y
• X - Proline
Y - Hydroxyproline
Ring structure stabilizes the triple helix
• Most abundant type – Type I Collagen, fibril forming
collagen.
• Type I Collagen has around 1000 amino acid residues or
about 330 Gly-X-Y repeats.

5. • In addition to fibrin forming collagen, there are also fibril
associated collagens, which bind to the fibrils and link them to
one another and to matrix.
• Type IV Collagen (network forming) form the basal laminae
(a layer of extracellular matrix secreted by the epithelial cells,
on which the epithelium sits)
In this, the Gly-X-Y repeats are frequently interrupted by short
non-helical sequences.
• Yet another collagen forms anchoring fibrils, which link basal
laminae to underlying connective tissues.
• Other types of collagen are transmembrane proteins that
participate in cell matrix interactions.

7. MATRIX POLYSACCHARIDES
• The fibrous proteins are embedded in gels formed from
polysaccharides called Glycosaminoglycans (GAGs)
• They contain repeating units of disaccharides.
• One sugar is either N-acetylglucosamine or N-
acetylgalactosamine and the second sugar is acidic, either
glucuronic acid or iduronic acid.
• These sugars are modified by sulfate groups, except
hyaluronan.
• Because of the negative charge, GAGs bind to positively
charged ions and trap water molecules, giving mechanical
support.

10. • Hyaluronan is the only GAG, that occur as a single long
polysaccharide chain. It is synthesized at the plasma
membrane by a transmembrane synthase.
• All other GAGs are linked to proteins to form proteoglycans,
which consist up to 95% polysaccharides by weight.
• Proteoglycans interact with hyaluronan to form large complexes
example aggregan.

11. MATRIX ADHESION PROTEINS
• Responsible for linking the components of the matrix to one
another and to the surface of the cells. Interact with collagen
and proteoglycans.
• The prototype of these molecules is Fibronectin
• It has binding sites for
both collagen and
GAGs, thus help in
crosslinking.
• They have distinct site
recognized by cell
surface receptors and
thus help in
attachment of matrix
to cells.

12. • Basal laminae has another adhesion protein called Laminin.
• Laminins are heterotrimers of alpha, beta and gama subunits.
• Synthesized in early embryos that do not contain collagen.
• They also has binding sites for cell surface receptors

13. • They are also tightly associated with another protein called
entactin, which also bind to type IV collagen.
• This multiple interactions will form cross linked networks in the
basal laminae.