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An enzyme is any protein that acts as a catalyst in living organisms. A catalyst is a chemical that mediates or speeds up a specific chemical reaction without being destroyed or altered upon completion of the reaction. Enzymes are also referred to as organic catalysts. Proteins, which consist of large complex molecules made up of one or more chains of amino acids, are the major structural component of all tissue of living organisms and are necessary for cell repair and muscular growth. They are a functional component of enzymes, hormones, structural elements, and antibodies, and they are used for energy only when carbohydrates and fats are not available. Enzymes differ from most other catalysts in that they are much more specific in terms of the chemical reactions that they promote. There are also some biochemical catalysts that are not proteins, namely RNA molecules. There are currently about 4,000 biochemical reactions that are promoted by enzymes. One of the numerous functions of enzymes is in the digestion of food, that is, breaking down larger food molecules into smaller ones so that they can be absorbed by the intestines. Different enzymes digest different food substances, such as starches, sugars and cellulose (in cows and other ruminants). There are differences in the digestive enzymes that are produced in different types of animals according to their diet, such as whether they are carnivorous or herbivorous. Scientists have been aware of enzymes for well in excess of a century. For example, in 1860 Louis Pasteur recognized that they were essential to fermentation, although he mistakenly assumed that their catalytic action resulted from the structure and life of yeast cells. In 1897 the German chemist Edward Buchner demonstrated that enzymes could function independently of cells. The first enzyme molecule to be isolated in pure crystalline form was urease, which was prepared from the jack bean in 1926 by the American biochemist J. B. Sumner. Urease breaks down urea, which is a waste product formed in the liver, into carbon dioxide and ammonia. The term enzyme derives from the Greek word zymosis, which means fermentation. Created October 23, 2006. |