Q.10 Hyaluronic acid is composed of:

1. D-Galactose and N-acetyl D-glucosamine

2. L-Iduronie acid and N-acetyl-D-galactosamine

3. D-Glucuronic acid and N-acetyl-D-galactosamine

4. D-Glucuronic acid and N-acetyl-D-glucosamine

Hyaluronic Acid Composition: D-Glucuronic Acid & N-Acetyl-D-Glucosamine

Hyaluronic acid (HA), a key glycosaminoglycan in connective tissues, consists of repeating disaccharide units. The correct answer is 4. D-Glucuronic acid and N-acetyl-D-glucosamine.

Correct Answer

Hyaluronic acid forms a linear polymer of alternating D-glucuronic acid (GlcUA) and N-acetyl-D-glucosamine (GlcNAc) units, linked by β-1,4 and β-1,3 glycosidic bonds. This non-sulfated structure provides hydration, viscosity, and space-filling roles in extracellular matrices like synovial fluid and skin.

Option Explanations

1. D-Galactose and N-acetyl D-glucosamine (Incorrect)

D-Galactose and N-acetyl-D-glucosamine form chondroitin sulfate or keratan sulfate, not hyaluronic acid. These sugars appear in other glycosaminoglycans but lack HA’s specific uronic acid component.

2. L-Iduronie acid and N-acetyl-D-galactosamine (Incorrect)

L-Iduronic acid with N-acetyl-D-galactosamine defines dermatan sulfate (formerly chondroitin sulfate B). This combination supports flexible tissues but differs from HA’s glucuronic acid and glucosamine backbone.

3. D-Glucuronic acid and N-acetyl-D-galactosamine (Incorrect)

D-Glucuronic acid paired with N-acetyl-D-galactosamine constitutes chondroitin sulfate, vital for cartilage resilience. HA uniquely uses N-acetyl-D-glucosamine instead of galactosamine.

4. D-Glucuronic acid and N-acetyl-D-glucosamine (Correct)

This disaccharide repeat (GlcUA-β1,3-GlcNAc-β1,4) polymerizes via hyaluronan synthases, yielding HA chains up to millions of daltons long. Synthesized at plasma membranes, it binds water extensively for lubrication and structural support.