Glycosaminoglycans and glyconjugates

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║ ASSIGNMENT: BIOCHEMISTRY ║

║ Glycosaminoglycans & Glycoconjugates – Structure & Functions ║

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🔷 1. INTRODUCTION

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**Glycosaminoglycans (GAGs):**

Linear, unbranched polysaccharides made of repeating disaccharides:

→ Amino sugar (GlcN or GalN)

→ Uronic acid (GlcA or IdoA)

✔ Highly negatively charged (due to sulfate + COOH groups)

**Glycoconjugates:**

Carbohydrates covalently linked to proteins or lipids:

→ Glycoproteins

→ Proteoglycans

→ Glycolipids

**Importance:**

• ECM structure  

• Cell signaling  

• Immunity  

• Drug targets (e.g., heparin)

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🔷 2. CHEMICAL STRUCTURE OF GAGs

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**General Pattern:**

[Uronic acid/Hexose] – [Hexosamine]

**Key Components:**

• GlcNAc → C₈H₁₅NO₆  

• GalNAc → C₈H₁₅NO₆  

• GlcA → C₆H₁₀O₇  

• IdoA → C₆H₁₀O₇  

• Sulfate → SO₄²⁻  

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🔹 **Types of GAGs**

1. **Hyaluronic Acid**

→ [GlcA–GlcNAc]ₙ  

✔ No sulfate  

✔ Not attached to protein  

Formula: C₁₄H₂₁NO₁₁  

2. **Chondroitin Sulfate**

→ [GlcA–GalNAc]ₙ  

✔ Sulfation at C4/C6  

Formula: C₁₄H₂₁NO₁₄S  

3. **Dermatan Sulfate**

→ [IdoA–GalNAc]ₙ  

✔ Epimerized from GlcA  

Formula: C₁₄H₁₉NO₁₇S₂  

4. **Heparin / Heparan Sulfate**

→ Highly sulfated  

✔ Contains GlcNS  

Formula: C₁₂H₁₈NO₁₉S₃  

5. **Keratan Sulfate**

→ [Gal–GlcNAc]ₙ  

✔ No uronic acid  

Formula: C₁₄H₂₃NO₁₄S  

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🔷 3. PROPERTIES & FUNCTIONS

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**Properties:**

• Highly negative  

• Binds large amounts of water  

• Extended structure  

• Forms gel-like ECM

**Functions:**

• Joint lubrication → Hyaluronic acid  

• Cartilage strength → Chondroitin sulfate  

• Anticoagulation → Heparin  

• Corneal clarity → Keratan sulfate  

**Mechanism Example:**

Heparin binds antithrombin III → inhibits clotting factors

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🔷 4. GLYCOCONJUGATES

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🔹 **Glycoproteins**

• Protein + short sugar chains  

• N-linked (Asn) / O-linked (Ser/Thr)  

Example: Antibodies  

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🔹 **Glycolipids**

• Lipid + carbohydrate  

Example: GM1 ganglioside  

Contains sialic acid (C₁₁H₁₉NO₉)

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🔹 **Proteoglycans**

• Protein + GAG chains (>50% carbohydrate)  

Example: Aggrecan  

**Linkage Structure:**

Ser–Xyl–Gal–Gal–GlcA  

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🔷 5. BIOLOGICAL & MEDICAL IMPORTANCE

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**Medical Uses:**

• Heparin → blood thinner  

• Hyaluronic acid → joint therapy & cosmetics  

**Diseases:**

• Arthritis → cartilage breakdown  

• Cancer → metastasis via heparanase  

• Viral infection → GAG binding (e.g., viruses attach to cells)

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🔷 6. CASE STUDIES

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**Aggrecan in Cartilage:**

• Holds water → shock absorption  

• Loss → osteoarthritis  

**Selectin Interaction:**

• sLeˣ carbohydrate → immune cell rolling  

• Important in inflammation  

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🔷 7. COMMON MISTAKES

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❌ All GAGs have uronic acid → FALSE  

❌ Heparin = Heparan sulfate → FALSE  

❌ All GAGs attach to proteins → FALSE  

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🔷 8. ADVANCED INSIGHTS

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

• Glycomics → study of glycans  

• Biomarkers → cancer detection  

• Glycoengineering → better drugs  

• HA nanoparticles → drug delivery  

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🔷 9. KEY POINTS

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

✔ GAGs = repeating disaccharides  

✔ Highly negatively charged  

✔ Provide hydration & strength  

✔ Important in immunity & disease  

✔ Used in medicine & research  

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🔷 10. CONCLUSION

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Glycosaminoglycans and glycoconjugates are essential biomolecules

that regulate structural support, signaling, immunity, and disease.

Their chemical complexity makes them critical in modern medicine,

drug design, and biotechnology.

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