type I collagen
Summary
Type I collagen is the most abundant collagen in the body, providing tensile strength to bone, skin, tendons, and ligaments. It is composed of two α1 chains and one α2 chain forming a triple helix, requiring vitamin C-dependent hydroxylation of proline and lysine residues for stability. Defects in type I collagen synthesis cause osteogenesis imperfecta.
Detail
Type I collagen is synthesized by fibroblasts and osteoblasts and constitutes ~90% of bone organic matrix, as well as being a major component of skin, tendon, ligament, cornea, and dentin. Synthesis involves intracellular steps (translation of pre-pro-α chains, hydroxylation of proline/lysine residues by prolyl and lysyl hydroxylase requiring vitamin C as a cofactor, glycosylation, and triple helix formation into procollagen) followed by extracellular steps (cleavage of terminal propeptides by procollagen peptidase to form tropocollagen, and cross-linking via lysyl oxidase to form mature collagen fibrils). Mutations in COL1A1 or COL1A2 genes (encoding the α1 and α2 chains) cause osteogenesis imperfecta, characterized by multiple fractures with minimal trauma, blue sclerae (thinning of scleral collagen revealing underlying choroidal veins), hearing loss (due to abnormal ossicles), and dental imperfections (dentinogenesis imperfecta). Vitamin C deficiency (scurvy) impairs hydroxylation, leading to weak collagen and manifestations like bleeding gums, poor wound healing, corkscrew hairs, and perifollicular hemorrhages. Ehlers-Danlos syndrome (particularly the arthrochalasia and classical types) can also involve type I collagen defects, causing hyperextensible skin and joint hypermobility. Clinically, type I collagen degradation products (e.g., C-terminal telopeptide, CTX) are used as biomarkers for bone turnover in osteoporosis monitoring. Understanding the collagen synthesis pathway is essential for high-yield board questions differentiating collagen types (I: bone/skin/tendon, II: cartilage, III: reticular/blood vessels, IV: basement membrane).
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- Lippincott Illustrated Reviews: Biochemistry
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.