Answer
Proteins are important substances - some think the most important chemical substances - of the body, which are macromolecules made up of smaller units. The basic units of protein structure are amino acids ( made up of atoms of carbon, hydrogen, oxygen and nitrogen). All proteins are made up of primary chains of amino acids called peptides. In this primary peptide chain the amino acids are linked by peptide bonds. This is the lowest level of protein structure, and there are few differences between fibrous and globular proteins at this level of organization. However,at the secondary, tertiary and quaternary levels proteins differ in structure, and on bases of those differences proteins are classified broadly into fibrous proteins and globular proteins.
At the secondary level of structure both fibrous and potential globular proteins are a still single polypeptide chain which coils and bends and turns to form strands and pleats. But while fibrous proteins form long threads and pleats , globular proteins tend to form shorter pleats and coils stabilized by hydrogen bonds. It is at the tertiary level that fibrous proteins become easily distinguishable in structure from globular proteins. This is the level of organization at which the three dimensional (3D) conformation of the molecules are formed. The alpha helices and long threads of fibrous proteins tend to become long rigid rods, while the tertiary structures of the globular proteins ( sort helices and sheets) fold in various ways to develop globular or spheroidal conformations.. At the quaternary level of organization, globular clusters of polypeptide molecules aggregate form subunits of large protein molecules as in hemoglobin. Fibrous proteins do not form quaternary structures.
Fibrous protein, also called scleroproteins, develop through primary secondary and tertiary levels of organization to assume have threadlike or pleated structures. They have no tertiary level of organization. Globular proteins ( sphaeroproteins) on the other hand have primary, secondary, tertiary and quarternary levels of organization. Fibrous proteins have regular repeating sequences of amino acids in their polypeptide chains while the amino acid sequences in the globular protein peptide do not repeat regularly. Fibrous proteins have strong intermolecular bonds, but the intermolecular bonding in fibrous proteins is weak. Regarding solubility, fibrous proteins are insoluble in water, weak acids and bases, but water, strong acids and strong basic solutions can dissolve globular proteins. Susceptibility to enzyme action and UV radiation damage are greater for globular proteins and they are more sensitive to temperature and pH changes in their environment.
Work Step by Step
Examples of fibrous proteins are elastin, fibrin, collagen, myosin and actin. There are more types of fibrous proteins than globular proteins. The former have greater tensile and mechanical strength and are important in structure muscles, tendons, and ligaments, for support, movement, and protection. Some common globular proteins are insulin. casein, hemoglobin, and albumins, While fibrous proteins constitute a greater percentage of the body than globular proteins, there are more kinds of globular proteins than fibrous proteins. Some important functions of globular proteins are work as enzymes(catalysts), chemical messengers(hormones), antibodies, membrane transport carriers and receptors.
