Another name for a vitamin is a coenzyme. In biochemistry, a coenzyme is a molecule that an enzyme needs to perform its function, but that the body can't produce itself. So coenzymes, or vitamins, must be acquired from dietary sources. A well-known example of a vitamin needed for enzyme activity is vitamin C.
Enzymes Catalyze Biochemical Reactions
Enzymes are protein molecules that catalyze biochemical reactions. Often, cellular reactions occur a million times faster in the presence of an enzyme than without the enzyme, and virtually all cellular processes depend on particular enzymes to do their work. All chemical reactions in living cells have at least three players: a reactant, an enzyme and a product. For example, carbonic anyhydrase is an enzyme that takes carbonic acid -- the reactant -- and splits it into water and carbon dioxide -- the products.
Some Enzymes Require Coenzymes
The enzyme carbonic anhydrase can only function in the presence of zinc. Like all enzymes, carbonic anhydrase works because it has a particular site called the active site that its reactant can fit into. Once there, the reactant will quickly be changed in a chemical reaction. In the case of carbonic anhydrase, carbonic acid splits into carbon dioxide and water when it is near the zinc ion that is located in the enzyme's active site. Without zinc, the electrons in carbonic acid that need to move to make the chemical reaction happen will not move, and nothing will happen to carbonic acid. Not all enzymes need coenzymes to function. Some use their own atoms to catalyze chemical reactions the way that zinc facilitates the activity of carbonic anhydrase.
Examples of Coenzymes
Many coenzymes are vitamins or derivatives of vitamins. These are organic molecules, and examples include vitamin C and the B vitamins. But some coenzymes are metal ions or other non-organic molecules. Zinc, copper, and iron ions are all common metallic coenzymes. The major reason we need these metals and vitamins in our diet is to supply enzymes with the coenzymes they need to function.
Vitamin C and Scurvy
Vitamin deficiencies can cause a wide range of medical problems, and a well-known example of a condition resulting from a vitamin deficiency is scurvy. Enzymes called hydroxylases are required to produce the collagen fibrils required for healthy skin, tendons, and blood vessels. These enzymes require vitamin C as a coenzyme, so without vitamin C, normal collagen fibrils cannot be made, and a weakening of the skin, tendons and blood vessels known as scurvy can result.
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