tailieunhanh - Encyclopedia Of Animal Science - O

Từ điển khoa học động vật vần O | Omega-3 and -6 Fatty Acids Brian K. Speake Peter F. Surai Scottish Agricultural College Ayr . INTRODUCTION Dietary fatty acids were originally thought to perform rather passive roles as a source of energy and cell membrane components. This view has now been transformed by the realization that omega-3 and omega-6 polyunsaturates are potent determinants of the body s physiological state regulating fuel partitioning inflammation and neurological function and are therefore crucial determinants of health disease and productivity. GENERAL ASPECTS Structures and Nomenclature A fatty acid molecule consists of a hydrocarbon chain with an acidic carboxyl group at one end and a terminal methyl group at the other. In the case of a saturated fatty acid all the carbon atoms in the chain are linked by single bonds whereas an unsaturated fatty acid is defined by the presence of one or more double bonds in the chain. Most polyunsaturated fatty acids of animal tissues belong to either the omega-6 o6 or omega-3 o3 series also referred to as n-6 and n-3 respectively . These terms indicate the positioning of the double bonds in the chain. Thus for an o6 fatty acid the double bond nearest to the methyl end is located between carbon atoms 6 and 7 counting from the methyl terminus. Similarly the double bond nearest to the methyl end of an o3 fatty acid forms the link between carbon atoms 3 and 4. Fatty acids are symbolized by a shorthand nomenclature. For example linoleic acid is abbreviated to 18 2o6 indicating a chain length of 18 carbon atoms with 2 double bonds the first double bond being located between carbons 6 and 7 from the methyl end. Other polyunsaturated fatty acids with important functions in animals are a-linolenic 18 3o3 arachidonic 20 4o6 eicosapentaenoic 20 5o3 and docosahexaenoic 22 6o3 acids. In the diets and tissues of animals fatty acids are mainly present in the esterified form as triacylglycerols phospholipids or cholesteryl esters with only traces occurring in .

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