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Chapter 16 : The Roles of Vitamins

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The Roles of Vitamins, Page 1 of 2

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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.

Citation: Gest H. 2003. The Roles of Vitamins, p 105-109. In Microbes. ASM Press, Washington, DC. doi: 10.1128/9781555817855.ch16
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Figures

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Figure 25

The pathway for combining a vitamin-containing coenzyme with its enzyme protein. The chain of amino acids forming the enzyme protein is represented here as a tubular structure that is folded in a specific way. The relative size of the vitamin-containing coenzyme is deliberately exaggerated; usually a coenzyme is only one-fiftieth to one-hundredth the size of the associated protein.

Citation: Gest H. 2003. The Roles of Vitamins, p 105-109. In Microbes. ASM Press, Washington, DC. doi: 10.1128/9781555817855.ch16
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Image of Figure 26
Figure 26

Complete chemical structure of the coenzyme nicotinamide adenine dinucleotide (NAD). The vitamin nicotinamide (niacinamide) (upper left) is part of the coenzyme molecule. This coenzyme is an essential “enzyme partner” in bioenergetic mechanisms.

Citation: Gest H. 2003. The Roles of Vitamins, p 105-109. In Microbes. ASM Press, Washington, DC. doi: 10.1128/9781555817855.ch16
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References

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Tables

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Table 8

Quantities of the vitamin niacin in some common foods

Citation: Gest H. 2003. The Roles of Vitamins, p 105-109. In Microbes. ASM Press, Washington, DC. doi: 10.1128/9781555817855.ch16

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