A Mucopolysaccharide that do not contain uronic acid (UA)
**Core Concept**
Mucopolysaccharides, also known as glycosaminoglycans (GAGs), are **complex carbohydrates** consisting of a core protein with one or more covalently attached GAG chains. They are key components of the **extracellular matrix** and play critical roles in various biological processes.
**Why the Correct Answer is Right**
The correct answer is related to the specific structure of mucopolysaccharides. Most mucopolysaccharides contain **uronic acid (UA)**, such as glucuronic acid or iduronic acid, as part of their disaccharide repeating units. However, one notable exception is **keratan sulfate**, which does not contain uronic acid. Instead, keratan sulfate is composed of repeating disaccharide units of galactose and **N-acetylglucosamine**.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because most mucopolysaccharides, such as **chondroitin sulfate** and **heparin**, do contain uronic acid.
**Option B:** Similarly, this option is incorrect as **dermatan sulfate** also contains iduronic acid, a type of uronic acid.
**Option D:** This option is incorrect as well, since **hyaluronic acid** is composed of glucuronic acid and **N-acetylglucosamine**, making it a mucopolysaccharide that contains uronic acid.
**Clinical Pearl / High-Yield Fact**
It's crucial to remember that **keratan sulfate** is unique among mucopolysaccharides due to its lack of uronic acid, which distinguishes it from other GAGs like chondroitin sulfate and hyaluronic acid.
**Correct Answer:** D. Keratan sulfate