Relationship of Form and Function in Globular and Fibrous Proteins
- The function of a protein is inherently tied to its structure.
- This relationship can be illustrated by comparing fibrous proteins and globular proteins, which are structurally distinct and suited to their specific roles in the body.
Fibrous Proteins Offer Strength and Support
- Fibrous proteins consist of elongated polypeptide chains that lack typical tertiary structures.
- Instead, their quaternary structure involves linking polypeptides into long fibres or filaments, stabilized by hydrogen bonds.
Collagen
- Quaternary Structure: Composed of three polypeptides twisted into a triple helix.
- Primary Structure: Features a repeating sequence of three amino acids, proline, glycine, and X (variable).
- Glycine, with its small R-group (a single hydrogen atom), faces inward, allowing the tight triple helix structure.
- Proline or hydroxyproline prevents the formation of alpha-helices, facilitating the triple helix.
Functionality
- Tensile Strength: Collagen’s rope-like triple helix provides structural integrity to tissues such as skin, tendons, ligaments, and cartilage.
- Variability: The R-group of the third amino acid is flexible, enabling different types of collagen for various functions (e.g., forming the basement membranes of epithelia and the outer layer of the eye).
