Fibrous/globular proteins
STRUCTURES.
Fibrous Proteins have little or no tertiary structure
(In other words no folding of the polypeptide chains.)
They consist of long parallel chains, with cross-links between the chains.
Long fibres and sheets are formed.
Globular Proteins have a complex tertiary structure.
The molecules take on a spherical (globular) shape, with polar groups directed outwards – increasing solubility in water.
Some also have a quarternary structure – defining how polypeptide molecules are arranged relative to one another.
Fibrous Proteins:
- Properties: Fibrous proteins are typically insoluble in water and play structural roles in the body, providing support, strength, and shape to cells and tissues.
- Examples: a. Collagen: Found abundantly in connective tissues such as tendons, ligaments, and skin, collagen provides tensile strength and structural support. b. Keratin: Present in hair, nails, and the outer layer of the skin (epidermis), keratin provides protection and mechanical strength. c. Fibroin: The main protein component of silk fibers produced by spiders and silkworms, fibroin is known for its strength and flexibility.
Globular Proteins:
- Properties: Globular proteins are generally soluble in water and exhibit a wide range of functions, including enzyme catalysis, transport, signaling, and immune response.
- Examples:
(a) Enzymes: Proteins such as amylase, catalase, and lipase are
enzymes that catalyse biochemical reactions in the body,
facilitating processes such as digestion, metabolism, and cellular
respiration.
(b) Hemoglobin: Found in red blood cells, hemoglobin binds and
transports oxygen from the lungs to tissues throughout the body,
as well as carbon dioxide from tissues to the lungs for exhalation. (c) Immunoglobulins (Antibodies): These proteins play a critical role
in the immune system by recognizing and binding to specific
antigens (foreign substances), marking them for destruction by
immune cells.
