Question

Which one of the following statements is NOT TRUE of glycosaminoglycans?

• A. ( Glycosaminoglycans are composed of repeating disaccharide units. )
• B. ( Glycosaminoglycans consist of amino sugars that are frequently sulfated. )
• C. ( Hyaluronic acid is an example of a glycosaminoglycan. )
• D. ( Methionine is the predominant amino acid to which glycosaminoglycan chains are conjugated to form proteoglycans.)

Hint:

In biochemistry, understanding the molecular structure and functional group involvement, such as sulfation and amino acid specificity in protein linkage, is crucial for grasping complex biochemical interactions and mechanisms.

Answer 1

The Correct Option is D

Glycosaminoglycans (GAGs) are a major component of the extracellular matrix and are involved in various biological processes. They are linked to core proteins to form proteoglycans, but the statement about methionine is incorrect. 
Analysis of Each Option: (A) Correct: Glycosaminoglycans are indeed composed of repeating disaccharide units, typically consisting of an amino sugar and a uronic sugar. 
(B) Correct: Many glycosaminoglycans contain amino sugars that are often sulfated, which is critical for their function in the body. 
(C) Correct: Hyaluronic acid is a well-known example of a glycosaminoglycan that does not contain sulfate groups and is not linked to a protein core. 
(D) Incorrect: Proteoglycans are formed when glycosaminoglycans are attached to a core protein, typically through a linkage involving the amino acid serine, not methionine. Conclusion:
Explanation: The correct linkage involves a specific region on the core protein where a xylose molecule binds to a serine residue, initiating the attachment of the glycosaminoglycan chain. Methionine is not involved in this process.