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).
Globular Proteins Are Precise and Versatile
Definition
Globular protein
Globular proteins are compact, spherical proteins that are typically soluble in water. Their structure results from the folding of the polypeptide chain into a tightly packed three-dimensional shape.
- Globular proteins have a rounded shape, formed by the folding of polypeptides into intricate structures.
- These shapes are stabilized by bonds between R-groups.
Insulin
- Conformation: Insulin’s specific three-dimensional shape allows it to bind precisely to insulin receptors on cells.
- Function: This precise binding triggers intracellular signals for glucose absorption, essential for maintaining blood sugar levels.
Functionality
The precise arrangement of atoms, known as conformation, is critical for the function of globular proteins. Examples include:
- Enzymes: Their active sites rely on the precise folding of R-groups to catalyze reactions.
- Receptors: Ligand-binding sites depend on specific protein conformations to transmit signals.
Comparing Fibrous and Globular Proteins
| Feature | Fibrous proteins | Globular proteins |
|---|---|---|
| Structure | Elongated, rope-like | Compact, spherical |
| Stability | Hydrogen bonds between chains | R-group interactions stabilize folding |
| Examples | Collagen | Insulin, enzymes |
| Function | Provides structural support | Catalysis, regulation, signaling |
- How does the structure of collagen enable it to withstand mechanical stress?
- Why is the conformation of globular proteins like insulin critical for their function?
