Overview
This lecture explains the structure, properties, and functions of fibrous proteins, focusing on collagen, keratin, and elastin.
Fibrous Proteins vs. Globular Proteins
- Fibrous proteins are long, rope-like, and provide structural support, unlike the spherical, water-soluble globular proteins.
- Fibrous proteins have a high proportion of hydrophobic amino acids, making them insoluble in water.
Collagen
- Collagen is found in tendons, ligaments, and skin and is a very strong protein.
- It consists of three polypeptide chains wrapped tightly into a triple helix.
- Every third amino acid in collagen is glycine, allowing tight wrapping due to glycine’s small side chain.
- Hydrogen bonds and strong crosslinks between chains stabilize collagen’s structure.
- Multiple triple helices combine to form larger fibers (microfibers and fibrils), arranged in a staggered pattern to prevent weak spots.
- Extra strength is added by cross-linking between different triple helical molecules.
Keratin
- Keratin is present in hair, fingernails, and the outer skin layer.
- It is extremely strong, insoluble in water, and made of long-stranded molecules.
- Keratin contains many cysteine amino acids, which form strong disulfide (covalent) bonds, contributing to its toughness.
Elastin
- Elastin is abundant in the skin and artery walls, providing elasticity and suppleness.
- Its long strands have hydrophobic regions and are cross-linked.
- Hydrophobic regions from different strands associate, clustering elastin molecules together.
- When stretched, strands move apart but remain attached at crosslinks, allowing elastin to stretch and recoil.
Key Terms & Definitions
- Fibrous Protein — A structural protein with a long, rope-like shape, insoluble in water.
- Globular Protein — A spherical, water-soluble protein with diverse functions.
- Collagen — A triple-helical, strong fibrous protein in skin, tendons, and ligaments.
- Glycine — The smallest amino acid, allowing tight packing in collagen.
- Keratin — A fibrous protein in hair, nails, and skin, strengthened by disulfide bonds.
- Cysteine — An amino acid that forms strong covalent disulfide bonds in keratin.
- Elastin — An elastic fibrous protein in skin and arteries, capable of stretching and recoiling.
Action Items / Next Steps
- Review the structures and functions of collagen, keratin, and elastin.
- Be able to compare fibrous and globular proteins for upcoming assessments.