Step by Step
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Overview and locations
Collagen is the most abundant protein in the human body — a fibrous structural protein found in skin, tendons, bones, and cartilage.
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The triple helix
Collagen's defining structural feature is its triple helix — three separate polypeptide chains wound together into a single, rope-like structure.
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Why glycine is essential every third position
Glycine, the smallest amino acid, must appear at every third position along each chain, since it's the only amino acid small enough to fit into the tightly packed center of the triple helix.
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Proline, hydroxyproline, and vitamin C
Proline and hydroxyproline add structural rigidity to the collagen molecule. Vitamin C is specifically required for the hydroxylation of proline (converting it to hydroxyproline) — a deficiency in vitamin C therefore impairs collagen synthesis, causing scurvy.
Applied Walkthrough
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As the most abundant protein in the human body, collagen provides the structural foundation for skin, tendons, bones, and cartilage — all relying on its defining triple helix, three separate polypeptide chains wound tightly together.
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This tight winding is only possible because glycine — the smallest of all amino acids — occupies every third position along each chain, since no larger amino acid could fit into the crowded center of the triple helix.
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Proline and hydroxyproline, positioned elsewhere along the chains, add crucial structural rigidity to the overall molecule.
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Converting proline into hydroxyproline specifically requires vitamin C — which is exactly why a vitamin C deficiency directly impairs collagen synthesis, producing the connective tissue breakdown characteristic of scurvy.
Exam Application
Exams test whether you know collagen's triple helix structure and why glycine must appear at every third position, and whether you understand the specific biochemical link between vitamin C deficiency and scurvy via impaired proline hydroxylation.
⚠ Common Trap
The most common trap is not connecting WHY vitamin C deficiency causes scurvy at the molecular level — it's specifically because vitamin C is required for hydroxylating proline into hydroxyproline, a step essential for stable collagen formation; without it, collagen synthesis is directly impaired.
✓ Quick Self-Check
1. What is collagen, and where is it found in the body?
The most abundant protein in the body, a fibrous structural protein found in skin, tendons, bones, and cartilage.
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2. What is collagen's defining structural feature?
A triple helix — three polypeptide chains wound together.
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3. Why must glycine appear at every third position in collagen's chains?
Because it's the smallest amino acid, and it's the only one small enough to fit into the tightly packed center of the triple helix.
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4. What do proline and hydroxyproline contribute to collagen?
Structural rigidity.
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5. What vitamin is required for collagen synthesis, and what deficiency disease results from its absence?
Vitamin C, required for hydroxylating proline; deficiency causes scurvy.
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