Glycosaminoglycans & Glycoproteins Overview

Role of GAGs in Ground Substance

• GAGs play a crucial role in maintaining the body's ground substance, providing structural support and facilitating cell-cell interactions.
• They act as a hydrated gel-like matrix, allowing for the diffusion of nutrients, waste, and signaling molecules.

Proteoglycans vs. Glycoproteins

• The main difference between proteoglycans and glycoproteins is the presence of a long, unbranched polysaccharide chain (GAG) in proteoglycans.
• Glycoproteins, on the other hand, have shorter, branched oligosaccharide chains.

Characteristics of GAGs

• GAGs are characterized by the presence of carboxyl and sulfate groups, which impart a high negative charge density.
• This high negative charge density is responsible for the retention of water and the creation of a hydrated gel-like matrix.

Significance of Carboxyl and Sulfate Groups

• The presence of carboxyl and sulfate groups in GAGs is significant, as they:
  • Attract and retain water, creating a hydrated matrix.
  • Provide a negative charge, influencing the behavior of surrounding molecules.

Amino Sugars in GAGs

• Glucosamine and galactosamine are the two amino sugars commonly found in the structure of GAGs.

Function of GAGs

• The large number of negative charges in GAGs allows them to:
  • Attract and retain water, creating a hydrated matrix.
  • Interact with positively charged molecules, influencing cell behavior.

Consistency of Mucous Secretions and Synovial Fluid

• The slippery consistency of mucous secretions and synovial fluid is due to the presence of GAGs, particularly hyaluronic acid.

Classification of GAGs

• GAGs are classified into several classes based on:
  • Monomeric composition.
  • Type of glycosidic linkages.
  • Degree and location of sulfate units.

Proteoglycan Aggregates

• Proteoglycan monomers associate with hyaluronic acid to form proteoglycan aggregates.
• These aggregates are stabilized by the interaction between proteoglycan monomers and hyaluronic acid.

Synthesis of GAGs

• The polysaccharide chains are elongated during GAG synthesis through the addition of monosaccharide units.
• This process occurs in the Golgi apparatus and endoplasmic reticulum.

Synthesis of Amino Sugars

• Glucosamine-6-phosphate (GlcN-6-P) is converted into N-Acetylglucosamine (GlcNAc) by replacing a hydroxyl group with an acetyl group.
• Similarly, galactosamine-6-phosphate (GalN-6-P) is converted into N-Acetylgalactosamine (GalNAc).

Proteoglycan Monomer Structure

• The carbohydrate chain is attached to the protein in the proteoglycan monomer through a glycosidic bond.