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تسجيل

Some polyunsaturated fatty acids cannot be synthesized by mammals and are nutritionally essential

المؤلف:  Peter J. Kennelly, Kathleen M. Botham, Owen P. McGuinness, Victor W. Rodwell, P. Anthony Weil

المصدر:  Harpers Illustrated Biochemistry

الجزء والصفحة:  32nd edition.p232

2025-07-16

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Certain long-chain unsaturated fatty acids of metabolic significance in mammals are shown in Figure 1. Other C₂₀ , C₂₂ , and C24 polyenoic fatty acids may be derived from oleic, linoleic, and α-linolenic acids by chain elongation. Palmitoleic and oleic acids are not essential in the diet because the tissues can introduce a double bond at the Δ⁹ position of a saturated fatty acid. Linoleic and α-linolenic acids are the only fatty acids known to be essential for the complete nutrition of many species of animals, including humans, and are termed the nutritionally essential fatty acids. In humans and most other mammals, arachidonic acid can be formed from linoleic acid.

Fig1. Structure of some unsaturated fatty acids. Although the carbon atoms in the molecules are conventionally numbered—that is, numbered from the carboxyl terminal—the ω numbers (eg, ω7 in palmitoleic acid) are calculated from the reverse end (the methyl terminal) of the molecules. The information in parentheses shows, for instance, that α-linolenic acid contains double bonds starting at the third carbon from the methyl terminal, has 18 carbons and 3 double bonds, and has these double bonds at the 9th, 12th, and 15th carbons from the carboxyl terminal. *Nutritionally essential fatty acids in humans.