Kids Research Express

Antibody, any of perhaps a million kinds of normally occurring protein molecules that are produced in the body of cells called lymphocytes and that act primarily as a defense against invasion by foreign substances. An important component of the immune system , antibodies are found in the blood of all vertebrates, in the fraction of the blood called gamma globulin. The synthesis, or manufacture, of antibodies is initiated when a foreign substance, referred to as an antigen , enters the body. Lymphocyte cells respond to the foreign substance by making an antibody with a molecular arrangement that fits the shape of molecules on the surface of the substance so that the antibody combines with it. Common antigens are the protein components of bacteria and viruses. These antigens may enter the body during infection or may be deliberately introduced by vaccination (see Immunization ) in order to stimulate the production of antibodies. The binding of antibodies to the surfaces of bacteria, viru

Unlike fibrous proteins, globular proteins are spherical and highly soluble. They play a dynamic role in body metabolism. Examples are albumin, globulin, casein, hemoglobin, all of the enzymes, and protein hormones. The albumins and globulins are classes of soluble proteins abundant in animal cells, blood serum, milk, and eggs. Hemoglobin is a respiratory protein that carries oxygen throughout the body and is responsible for the bright red color of red blood cells. More than 100 different human hemoglobins have been discovered, among which is hemoglobin S, the cause of sickle-cell anemia , a hereditary disease suffered mainly by blacks. A Enzymes All of the enzymes are globular proteins that combine rapidly with other substances, called substrate, to catalyze the numerous chemical reactions in the body. Chiefly responsible for metabolism and its regulation, these molecules have catalytic sites on which substrate fits in a lock-and-key manner to trigger and control metabolism throughout