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Functions of Protein

Proteins are responsible for various functions in the body of living organisms. Enzymatic proteins Function: Selective acceleration of chemical reactions Example: Digestive enzymes catalyze the hydrolysis of bonds in food molecules. Storage proteins Function: Storage of amino acids Examples: Casein, the protein of milk, is the major source of amino acids for baby mammals. Plants have storage proteins in their seeds. Ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo. Hormonal proteins Function: Coordination of an organism‘s activities Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration. Contractile and motor proteins; Function: Movement Examples: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles. Defensive proteins; Function: Protection against disease Example: Antibodies inactivate and help destroy viruses and bacteria. Transport proteins; Function: Transport of substances Examples: Hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from the lungs to other parts of the body. Other proteins transport molecules across membranes. Receptor proteins; Function: Response of cell to chemical stimuli Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells. Structural proteins; Function: Support Examples: Keratin is the protein of hair, horns, feathers, and other skin appendages. Insects and spiders use silk fibers to make their cocoons and webs, respectively. Collagen and elastin proteins provide a fibrous framework in animal connective tissues.