Connective Tissues

The Connective tissue is formed by

Cells and Extracellular matrix

(Intercellular matrix)

Extracellular Matrix

Function

• Stabilization of tissue structure.
• Regulation cell behavior
  • Survival, development, migration, proliferation.
• Membrane filtration barrier (glomerules).
• Exchange of different metabolites, ions and water.
• Reparation function.
• Immune processes.
• Participation in inflammation.

Cells of Connective Tissue

• Fibroblasts
• Chondroblasts ( cartilage ).
• Osteoblasts ( bone ).
• Odontoblasts ( tooth ).

These cells synthesize extracellular matrix.

Parts of the extracellular matrix

FIBRILLAR PROTEINS ( collagen, elastin )

• Insoluble in water, no hydratation

GLYCOPROTEINS ( example : fibronectin, laminin ).

GLYCOSAMINOGLYCANS AND PROTEOGLYCANS

• Soluble in water, easily hydratated.

Extracellular matrix

Fibrillary Proteins :

• Structural Proteins
  • Collagen – Firmness
  • Elastin – elasticity

COLLAGENS

The most abundant proteins in mammals. They form approximately 25% of all body proteins.

Collagenum

Gr; kolla glue;

Gr; gennao constitute

By boiling collagen is denatured to a colloid solution (gelatine). From the non- purified collagen the glue arises.

• Main protein of the extracellular matrix.
• Component of tendons, cartilages, bones, and teeth ( dentin and cement), skin and vessels.

Properties

• Fibrillary proteins.
• Non soluble ( Glyco-) proteins.
• HIGH STRENGTH, BUT ALSO SUPPLENESS.

Structure of Collagen

Collagen has a Characteristic amino acid composition and their specific sequence.

Primary Structure

• Characteristic AA Composition
• Characteristic AA Sequence

Mature collagen contains no tryptophan and almost no cysteine- from the nutritional point of view not fully valuable protein.

Characteristic AA Composition

• Fundamental amino acids
  • Glycine 33 % (x Hb 4 %)
  • Proline 13 % (x Hb 5%)
    • High content
• Derived amino acids
  • 4- Hydroxyproline 9 % (x Hb 0%)
  • 5- Hydroxylysine 0.6 %(x Hb 0%)
    • Characteristic for collagen
    • Origin by post translational modification

Read this topic also Overview of Cell injury and it’s Mechanic

Characteristic AA Sequence

• Every third AA is GLYCINE.
• On the next position frequently PROLINE.
• On the third position frequently hydroxyproline, ev. Hydroxylysine.

Example of AA sequence of a part of the polypeptide chain

Secondary structure of collagen

Comparison of collagen helix to the alpha helix, which represents the most common secondary structure in proteins.

Collagen helix

• Levorotatory helix
• Steeper rising
• 3.3 AA / turn
• Intrachain hydrogen bonds not present
• Proline prevents formation of alpha-helix or beta- pleated sheet

Alpha- helix (the most common secondary structure in proteins)

• Dextrorotatory helix
• Gradual rising
• 3.6 AA / turn
• Stabilization by intrachain hydrogen bonds

Triple helix

This structure is responsible for the tensile strenght.

The origin is dependent on the oddness of the primary structure

• High presence of Glycine
  • Smallest amino-acid, no side chain (only -H)
  • Placed in the centre of triple helix, where no space is available
  • Close contact between the chains

Triple helix is stabilized by hydrogen bonds between each peptide bond -NH group of glycine and C=O group of the peptide bond of the adjacent polypeptide chain.