Q.93 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.
Option D is NOT TRUE. Glycosaminoglycans (GAGs) are key polysaccharides in extracellular matrices, and understanding their properties is crucial for CSIR NET Life Sciences preparation. This MCQ tests core concepts in biochemistry and proteoglycans.
Option Analysis
Glycosaminoglycans feature repeating disaccharide units, often with sulfated amino sugars, and specific linkage chemistry in proteoglycans.
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(A) TRUE: Glycosaminoglycans consist of repeating disaccharide units, typically an amino sugar (like GlcNAc or GalNAc) alternating with a uronic acid (GlcA or IdoA).
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(B) TRUE: They contain amino sugars that are frequently sulfated at various positions, such as C4, C6, or nitrogen, contributing to their negative charge.
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(C) TRUE: Hyaluronic acid is a nonsulfated glycosaminoglycan made of repeating GlcNAc-GlcA disaccharides, found in connective tissues.
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(D) NOT TRUE: Glycosaminoglycan chains in proteoglycans attach to serine residues via a xylose-based tetrasaccharide linker (Xyl-Gal-Gal-GlcA) on Ser-Gly sites, not methionine.
Glycosaminoglycans (GAGs), often called mucopolysaccharides, are long, negatively charged polysaccharides vital for extracellular matrix structure, cell signaling, and tissue hydration. Glycosaminoglycans structure features repeating disaccharide units that make them essential in biology exams like CSIR NET Life Sciences. This guide analyzes the MCQ “Which one of the following statements is NOT TRUE of glycosaminoglycans?” with detailed explanations.
Glycosaminoglycans Key Properties
GAGs like chondroitin sulfate, heparan sulfate, keratan sulfate, and hyaluronic acid share core traits:
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Repeating disaccharide units (e.g., GlcNAc/GlcA or GalNAc/GlcA).
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Amino sugars frequently sulfated for charge and interactions.
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Roles in lubrication, anticoagulation, and growth factor binding.
Hyaluronic acid exemplifies a nonsulfated GAG, unique as it is not covalently linked to proteins.
Proteoglycans and GAG Conjugation
Proteoglycans form when GAG chains attach to core proteins via O-glycosidic linkage. The process starts with xylosyltransferase adding xylose to serine in a Ser-Gly motif, followed by Gal-Gal-GlcA linker. Methionine plays no role; serine is predominant. This specificity explains why option D fails.
| Feature | TRUE Statements (A-C) | FALSE Statement (D) |
|---|---|---|
| Disaccharide Units | Repeating (e.g., HA: GlcNAc-GlcA) | N/A |
| Amino Sugars | Sulfated (e.g., C6-GlcNAc) | N/A |
| Example | Hyaluronic acid | N/A |
| Conjugation Amino Acid | N/A | Methionine (actual: Serine) |
CSIR NET Exam Tips
Focus on GAG biosynthesis, sulfation patterns, and proteoglycan linkers for scoring. Practice similar MCQs on glycosaminoglycans proteoglycans conjugation to master biochemistry units.
