🦴 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

Type	Location	Function	Clinical Notes
Type I 🦴	Bone, skin, tendon, dentin, fascia, cornea, late wound repair	90% of body collagen. Strong tensile support.	Defective in osteogenesis imperfecta.
Type II 🎧	Cartilage, vitreous body, nucleus pulposus	Structural support for cartilage + eye.	Mnemonic: “Type II = Cartwolage”
Type III ❤️	Skin, blood vessels, uterus, fetal tissue, early wound healing	Support in soft tissues + early repair.	Deficient in vascular Ehlers-Danlos (threE D).
Type IV 🏠	Basement membranes (glomeruli, cochlea, lens)	Filtration + structural base.	Defective in Alport syndrome; target in Goodpasture. Mnemonic: “Type IV = under the floor”.

🧠 Mnemonic: SCAB

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

⚙️ Steps of Collagen Synthesis

📜 Translation → Preprocollagen (Gly–X–Y motif; X=proline, Y=hydroxyproline/lysine).
🍊 Hydroxylation of proline & lysine (Vit C dependent) → deficiency = scurvy.
🍬 Glycosylation of hydroxylysine → forms procollagen triple helix.
📦 Exocytosis of procollagen.
✂️ Proteolytic cleavage → tropocollagen.
📏 Assembly → fibril formation.
🔒 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. 💪

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Collagen

✨ About Collagen

📊 Types of Collagen

🧠 Mnemonic: SCAB

⚙️ Steps of Collagen Synthesis

📌 Quick Summary

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