Biochemistry 2280A Lecture Notes - Lecture 5: Triple Helix, Protein Precursor, Alpha Helix
28 Oct 2016
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Extracellular, forms strong fibers or sheets made in cell but lives life outside of cell. Connects and strengthens tissues: bone matrix, tendons, connective tissue, skin. Family of proteins, number i to xiv. Characteristic structure triple helical: 3 polypeptides braided together. Molecules join end to end which is why fiber is much longer than a single molecule. Proline is present: cyclic: even though proline is a helix breaker of the alpha helix but triple helix is different and proline is essential. Each collagen molecule is a triple helix: 3 polypeptides coming together: more extended than the alpha helix. Presence of so much proline prevents alpha helix. Every 3 residue is proline and they repel each other, locking polypeptides. Molecules repel each other when they get too close. Each proline is slotted in just the right distance from its neighbours. Locked in particular arrangement and can(cid:495)t move because would encounter repulsion from neighbours: 3 residues per turn.
