Overview
This lecture covers the structure, properties, and roles of fibrous proteins—specifically collagen, keratin, and elastin—highlighting their biological significance.
Fibrous Proteins: General Structure & Properties
- Fibrous proteins are one category of proteins, distinct from globular proteins.
- Their structure is determined by primary, tertiary, and quaternary protein structures.
- Fibrous proteins have long polypeptide chains with repeating amino acid sequences.
- They often have non-polar (hydrophobic) R groups, making them insoluble in water.
- These proteins form fibers, giving them great strength when multiple chains are wound together.
- Fibrous proteins typically have structural roles in the body.
Collagen
- Collagen is one of the most abundant fibrous proteins in the body.
- It forms strong fibers that provide strength to various tissues.
- Collagen is found in artery walls, preventing them from bursting under high blood pressure.
- It composes tendons, connecting muscles to bones and enabling movement.
- Collagen adds toughness and rigidity to bones for structural support.
Keratin
- Keratin is a very hard and strong fibrous protein.
- Found in fingernails, horns, and hooves—areas exposed to mechanical stress.
- Contains a high amount of cysteine, an amino acid with sulfur in its R group.
- Disulfide bridges form between cysteine residues, making keratin tough and durable.
Elastin
- Elastin is a fibrous protein with elastic properties; it can stretch and recoil.
- Elastin molecules are coiled and cross-linked, allowing tissues to stretch without breaking.
- Present in lungs (enabling inflation/deflation), bladder (allowing expansion), and artery walls (helping maintain blood pressure by stretching and recoiling).
Key Terms & Definitions
- Fibrous protein — A long, strong, insoluble protein with a structural role in organisms.
- Collagen — A fibrous protein that provides strength to tissues like arteries, tendons, and bones.
- Keratin — A hard, strong fibrous protein found in nails, horns, and hooves; strengthened by disulfide bonds.
- Elastin — A stretchy fibrous protein that allows tissues to expand and return to shape.
- Cysteine — An amino acid with a sulfur-containing R group, allowing disulfide bond formation.
- Disulfide bridge — A strong, covalent bond between two cysteine residues in proteins.
Action Items / Next Steps
- Review examples and functions of collagen, keratin, and elastin.
- Study the structural differences between fibrous and globular proteins.