polyunsaturated fatty acid
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polyunsaturated fatA saturated fatty acid (i.e., an alkyl-chain fatty acid) with two or more ethylenic carbon–carbon double bonds; because of the double bond, not every carbon is saturated with hydrogen atoms—i.e., there are fewer hydrogens—which reduces the strength of the compound's intermolecular forces, resulting in a significant lowering of the compound’s melting point.
Polyunsaturated fats in humans
• Linoleic PFAs—two double bonds between 9/10 (Δ9) and 12/13 (Δ12); e.g., CnH2n-COOH.
• Linolenic PFAs—three double bonds, Δ9, Δ12, Δ15; e.g., CnH2n-5-COOH.
• 4-doubled bond PFAs—four double bonds, Δ5, Δ8, Δ11, Δ14; e.g., arachidonic acid.