# DBT JRF 2020 — Question 88

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Easy

## Question

The mucopolysaccharide hyaluronic acid is composed of

## Options

- **A.** neither N-acetyl D-glucosamine nor D-glucuronic acid
- **B.** D-glucuronic acid only
- **C.** N-acetyl D-glucosamine only
- **D.** both N-acetyl D-glucosamine and D-glucuronic acid

## Answer

Option D

## Explanation

Hyaluronic acid (hyaluronan, HA) is a high-molecular-weight glycosaminoglycan (GAG) and a major component of the extracellular matrix (ECM), synovial fluid, and vitreous humour. Repeat disaccharide unit: $[\beta$ -D-glucuronic acid- $\beta$ (1→3)- $N$ -acetyl- $\beta$ -D-glucosamine $-\beta$ (1→4)]_n $. The two sugars alternate: GlcUA linked$ \beta $-1,3 to GlcNAc; GlcNAc linked$ \beta $-1,4 to the next GlcUA. HA is not sulphated (unlike heparan sulphate, chondroitin sulphate). HA is synthesised by HAS (hyaluronan synthase) at the plasma membrane, directly extruded into the ECM. MW can reach$ 10^6 $–$ 10^7$ Da. Functions: joint lubrication, space-filling, cell signalling via CD44 and RHAMM receptors, wound healing.

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