Biochemistry of connective tissue.

FUNCTIONS of connective tissue

• Transport • Immunological defense • Mechanical support • Growth and repair • Haemopoiesis

Collagen is the major structural protein of vertebrate extracellular matrix.

Types of collagen Collagen type I

i)The fibers have diameter between 80 to 160nm. ii)Found in bone, dentin, skin, tendon, muscles and walls of blood vessels.

Collagen type IIi)have a diameter <80nmii)found in invertiberal discs and hyaline cartilage.

Collagen type III i)Found in spleen, muscle, and aorta.

Collagen type IVFound around different types of in the basement membranes and muscles.

Collagen type VIt is found in embryonic cell cultures and the basement membranes.

Collagen type VI It is found in muscle and skin.

SCANNING ELECTRON MICROGRAPH OF DENSE COLLAGEN FIBERS OF GINGIVA

Collagen acts as the support structure in tissues and facilitates the live and function of cells.

HEALTHY GINGIVA CONTAINS MANY FIBROBLASTS AND A FEW INFLAMMATORY CELLS SUCH AS MACROPHAGES ,NEUTROPHILS, PLASMA CELLS AND LYMPHOCYTES.

Collagen

• a. protein high in content of AA, glycine, proline, hydroxyproline and many AA missing

• b. Protein helix is linearly oriented-3 chains twisted around each other in a fibril. H bonding between the chains.

The hierarchical design of collagen.

The structural features of collagen ranges from the amino acid sequence, tropocollagen molecules, collagen fibrils to collagen fibers.

• The tropocollagen cables are lined up head-to-tail in rows that are staggered by 64 nm along their long axes and crosslinked at their ends to improve strength

The synthesis of collagen molecules

Collagen molecules are crosslinked into fibrils: oxidative deamination of hydroxylysine and lysine forms reactive aldehyde groups, which link molecules together (and also link α-chains together too).

Collagen and elastin. • Elastin polypeptide

chains are cross-linked together to form rubberlike, elastic fibers.

• Each elastin molecule uncoils into a more extended conformation when the fiber is tretched and recoils spontaneously as soon as the stretching force is relaxed.

Elastin is a protein in connective tissue that is elastic and allows many tissues in the

body to resume their shape after stretching

or contracting. • Elastin serves an

important function in arteries and is particularly abundant in large elastic blood vessels such as the aorta. Elastin is also very important in the lungs, elastic ligaments, the skin, the bladder, elastic cartilage

• Elastin is primarily composed of the amino acids glycine, valine, alanine, and proline. It is a specialized protein with a molecular weight of 64 to 66 kDa, and an irregular or random coil conformation made up of 830 amino acids.

• Elastin is made by linking many soluble tropoelastin protein molecules, in a reaction catalyzed by lysyl oxidase, to make a massive insoluble, durable cross-linked array. The amino acid responsible for these cross-links is lysine.

Desmosine and isodesmosine are both found in elastin.

Proteoglycans• Proteoglycans are proteins

modified by glycosaminoglycans (GAG, mucopolysaccharides).

• Glycosaminoglycans are long-chain compounds made up of hundreds repeating disaccharide units. One of the sugars in each disaccharide unit is a hexosamine (glycosamine).

• Many proteoglycans contain a core protein which links them to the cellular membrane.

The four main types consist mainly of sulfated heparan sulfate/heparin, chondroitin sulfate/dermatan, keratan sulfate, and

the non-sulfated glycosaminoglycan hyaluronic acid.

• Hyaluronic acid is an extremely long and rigid glycosaminoglycan

• contains several thousand sugars but no protein core

• Linker molecules join proteoglycans to hyaluronic acid.

Disorders of connective tissue

• Ehlers-Danlos syndrome - deficient type III collagen- a genetic disease causing progressive deterioration of collagens, with different EDS types affecting different sites in the body, such as joints, heart valves, organ walls, arterial walls, etc.

• Marfan syndrome - a genetic disease causing abnormal fibrillin.

• Scurvy - dietary deficiency in vitamin C, leading to abnormal collagen.

(hemorrhages, loose of teeth, gums swell and bleed easily)

• Osteogenesis Imperfecta results in a dramatic weakening in the structure of bone, which leads to frequent fractures occurring at an early age. The fractures, in turn, lead to permanent deformaties of the extremities.