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Berg JM, Tymoczko JL, Stryer L. Biochemisattempt. 5th edition. New York: W H Freeman; 2002.
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Amongst the many biologically considerable properties of lipids are their hydrophobic properties. These properties are largely due to a details component of lipids: fatty acids, or sindicate fats. Fatty acids additionally play important functions in signal-transduction pathmethods (Sections 15.2 and 22.6.2).
12.2.1. The Naming of Fatty Acids
Fatty acids are hydrocarbon chains of assorted lengths and levels of unsaturation that terminate via carboxylic acid teams. The systematic name for a fatty acid is derived from the name of its parent hydrocarbon by the substitution of oic for the last e. For instance, the C18 saturated fatty acid is dubbed octadecanoic acid because the parent hydrocarbon is octadecane. A C18 fatty acid with one double bond is dubbed octadecenoic acid; via two double bonds, octadecadienoic acid; and through three double bonds, octadecatrienoic acid. The notation 18:0 denotes a C18 fatty acid with no double bonds, whereas 18:2 signifies that there are 2 double bonds. The structures of the ionized develops of 2 prevalent fatty acids—palmitic acid (C16, saturated) and also oleic acid (C18, monounsaturated)—are shown in Figure 12.2.
Structures of Two Fatty Acids. Palmitate is a 16-carbon, saturated fatty acid, and oleate is an 18-carbon fatty acid with a single cis double bond.
Fatty acid carbon atoms are numbered founding at the carboxyl terminus, as presented in the margin. Carbon atoms 2 and 3 are often referred to as α and β, respectively. The methyl carbon atom at the distal end of the chain is dubbed the ω-carbon atom. The position of a double bond is represented by the symbol Δ followed by a supermanuscript number. For example, cis-Δ9 suggests that tright here is a cis double bond in between carbon atoms 9 and also 10; trans-Δ2 indicates that tright here is a trans double bond in between carbon atoms 2 and also 3. Additionally, the place of a dual bond deserve to be deprovided by counting from the distal end, through the ω-carbon atom (the methyl carbon) as number 1. An ω-3 fatty acid, for example, has actually the framework displayed in the margin. Fatty acids are ionized at physiological pH, and so it is appropriate to describe them according to their carboxylate form: for example, palmitate or hexadecanoate.
12.2.2. Fatty Acids Vary in Chain Length and Degree of Unsaturation
Fatty acids in organic units usually contain an even number of carbon atoms, typically between 14 and 24 (Table 12.1). The 16- and 18-carbon fatty acids are a lot of common. The hydrocarbon chain is almost invariably unbranched in animal fatty acids. The alkyl chain may be saturated or it may contain one or even more double bonds. The configuration of the double bonds in the majority of unsaturated fatty acids is cis. The double bonds in polyunsaturated fatty acids are separated by at leastern one methylene team.
The properties of fatty acids and of lipids obtained from them are markedly dependent on chain size and level of saturation. Unsaturated fatty acids have actually reduced melting points than saturated fatty acids of the very same size. For example, the melting suggest of stearic acid is 69.6°C, whereas that of oleic acid (which has one cis double bond) is 13.4°C. The melting points of polyunsaturated fatty acids of the C18 series are even lower. Chain length additionally affects the melting allude, as portrayed by the reality that the melting temperature of palmitic acid (C16) is 6.5 degrees lower than that of stearic acid (C18). Therefore, brief chain length and also unsaturation improve the fluidity of fatty acids and also of their derivatives.
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