Chapter 16 : The Roles of Vitamins

Abstract:

Vitamins deserve special attention for several reasons. They are chemical substances required for normal functions in all cells and organisms, from microbes to humans. The remarkable aspect of vitamin function is that only very small quantities are needed for normal growth and maintenance of living cells. The word vitamin was coined in 1912 to describe substances that were thought to belong to a category of organic compounds called amines that were vital for survival of certain microbes and health in humans and various animals. This resulted in the term vit-amines or simply "vitamins. It turned out that as more and more vitamins were discovered and characterized, some of them were actually not amines, but the name stuck. Vitamins are organic compounds of relatively small size (as compared with macromolecules such as proteins). As far as is known, all vitamins perform their vital functions in association with particular enzymes that are essential for normal metabolism. Vitamins form parts of various coenzymes and since these coenzymes are, in turn, parts of (catalytic) enzymes, it follows that vitamins must also act in "catalytic quantities". This explains why vitamins are required in only trace amounts. The principle of vitamin action is illustrated in this chapter. The function of vitamins can perhaps be made clearer by a concrete example. The B-vitamin niacin is an excellent case in point. The human body is unable to synthesize niacin or niacinamide, and therefore we must obtain this B-vitamin from animal, plant, or microbial foods that we consume.