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Berg JM, Tymoczko JL, Stryer L. Biochemistry. Fifth edition. New York: W H Freeman; 2002.


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Among the many biologically far-ranging properties that lipids room their hydrophobic properties. These properties room mainly as result of a details component that lipids: fat acids, or simply fats. Fat acids likewise play necessary roles in signal-transduction pathways (Sections 15.2 and also 22.6.2).


12.2.1. The specify name of fatty Acids

Fatty acids room hydrocarbon chain of assorted lengths and also degrees that unsaturation the terminate v carboxylic mountain groups. The organized name for a fatty mountain is acquired from the surname of its parental hydrocarbon by the substitution the oic because that the last e. Because that example, the C18 saturated fatty mountain is dubbed octadecanoic acid since the parental hydrocarbon is octadecane. A C18 fat acid v one double bond is referred to as octadecenoic acid; through two double bonds, octadecadienoic acid; and also with three twin bonds, octadecatrienoic acid. The notation 18:0 denotes a C18 fat acid through no dual bonds, whereas 18:2 signifies that there are two double bonds. The structures of the ionized creates of two common fatty acids—palmitic acid (C16, saturated) and oleic acid (C18, monounsaturated)—are presented in figure 12.2.

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Figure 12.2

Structures of two Fatty Acids. Palmitate is a 16-carbon, saturated fatty acid, and oleate is an 18-carbon fat acid through a single cis twin bond.


Fatty mountain carbon atoms room numbered starting at the carboxyl terminus, as presented in the margin. Carbon atoms 2 and also 3 are often referred to together α and also β, respectively. The methyl carbon atom at the distal finish of the chain is called the ω-carbon atom. The position of a dual bond is stood for by the price Δ complied with by a superscript number. Because that example, cis-Δ9 means that over there is a cis double bond in between carbon atoms 9 and also 10; trans-Δ2 method that there is a trans double bond between carbon atoms 2 and 3. Alternatively, the place of a dual bond can be denoted by counting native the distal end, v the ω-carbon atom (the methyl carbon) as number 1. One ω-3 fat acid, because that example, has the structure presented in the margin. Fatty acids are ionized at physiological pH, and also so it is appropriate to describe them follow to their carboxylate form: because that example, palmitate or hexadecanoate.


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12.2.2. Fatty Acids differ in Chain Length and Degree that Unsaturation

Fatty acids in organic systems commonly contain an even variety of carbon atoms, typically between 14 and also 24 (Table 12.1). The 16- and also 18-carbon fat acids are most common. The hydrocarbon chain is virtually invariably unbranched in pet fatty acids. The alkyl chain may be saturation or it may contain one or more dual bonds. The configuration of the double bonds in many unsaturated fatty acids is cis. The double bonds in polyunsaturated fat acids are separated by at least one methylene group.


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The nature of fatty acids and also of lipids obtained from them are markedly dependent on chain length and degree of saturation. Unsaturated fatty acids have actually lower melting points than saturated fat acids the the very same length. Because that example, the melting allude of stearic mountain is 69.6°C, whereas the of oleic mountain (which has one cis double bond) is 13.4°C. The melting points the polyunsaturated fatty acids the the C18 series are also lower. Chain length also affects the melt point, as portrayed by the fact that the melting temperature of palmitic acid (C16) is 6.5 levels lower 보다 that that stearic acid (C18). Thus, brief chain length and also unsaturation improve the fluidity of fat acids and of your derivatives.

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