Makindo Medical Notes

✨ About Collagen

• 🦴 Most abundant protein in the body – found in skin, bone, cartilage, vessels, and connective tissue.
• 🔗 Composed of 3 α-chains forming a triple helix (not 4) → gives tensile strength.
• 🍖 Rich in glycine, hydroxyproline, and hydroxylysine → essential for stability.
• 🍊 Vitamin C needed for proline hydroxylation → deficiency = scurvy (poor wound healing, bleeding gums).
• 🧬 MMPs break down collagen during remodeling.
• 👁️ Type IV = basement membranes (kidney glomerulus, eye lens).
• 💥 Type I defect → osteogenesis imperfecta (brittle bones).
• ❤️ Type III defect → vascular Ehlers-Danlos (arterial rupture risk).
• ⚙️ Defects in enzymes (e.g. lysyl hydroxylase) → abnormal cross-linking.

📊 Types of Collagen

🧠 Mnemonic: SCAB

• S – Skeleton (Type I)
• C – Cartilage (Type II)
• A – Arteries (Type III)
• B – Basement membrane (Type IV)

⚙️ Steps of Collagen Synthesis

1. 📜 Translation → Preprocollagen (Gly–X–Y motif; X=proline, Y=hydroxyproline/lysine).
2. 🍊 Hydroxylation of proline & lysine (Vit C dependent) → deficiency = scurvy.
3. 🍬 Glycosylation of hydroxylysine → forms procollagen triple helix.
4. 📦 Exocytosis of procollagen.
5. ✂️ Proteolytic cleavage → tropocollagen.
6. 📏 Assembly → fibril formation.
7. 🔒 Cross-linking (lysyl oxidase, copper-dependent) → strong fibers. Defect = Menkes disease (weak collagen).

📌 Quick Summary

🦴 Collagen = body’s main structural protein. 🔢 Four main types (I–IV) remembered by SCAB. 🍊 Vitamin C deficiency = scurvy. 💥 Genetic defects → osteogenesis imperfecta, Ehlers-Danlos, Alport syndrome. ⚙️ Synthesis = translation → hydroxylation → glycosylation → triple helix → secretion → cleavage → cross-linking. Collagen gives tissues strength, flexibility, and repair capacity. 💪