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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 the lipids space their hydrophobic properties. This properties are mainly due to a specific component the lipids: fat acids, or merely fats. Fatty acids likewise play important roles in signal-transduction pathways (Sections 15.2 and also 22.6.2).


12.2.1. The naming of fat Acids

Fatty acids space hydrocarbon chains of miscellaneous lengths and also degrees the unsaturation the terminate through carboxylic mountain groups. The methodical name for a fatty mountain is derived from the surname of its parent hydrocarbon through the substitution of oic for the final e. For example, the C18 saturation fatty acid is called octadecanoic acid since the parent hydrocarbon is octadecane. A C18 fatty acid through one dual bond is referred to as octadecenoic acid; v two dual bonds, octadecadienoic acid; and with three double bonds, octadecatrienoic acid. The notation 18:0 denotes a C18 fatty acid with no double bonds, conversely, 18:2 signifies that there space two twin bonds. The frameworks of the ionized creates of two usual fatty acids—palmitic mountain (C16, saturated) and also oleic mountain (C18, monounsaturated)—are displayed in number 12.2.

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Figure 12.2

Structures of 2 Fatty Acids. Palmitate is a 16-carbon, saturated fat acid, and oleate is one 18-carbon fatty acid v a solitary cis twin bond.


Fatty acid carbon atoms space numbered beginning at the carboxyl terminus, as displayed in the margin. Carbon atom 2 and also 3 are often referred to together α and β, respectively. The methyl carbon atom at the distal finish of the chain is referred to as the ω-carbon atom. The place of a dual bond is stood for by the symbol Δ followed by a superscript number. Because that example, cis-Δ9 means that over there is a cis dual bond in between carbon atoms 9 and also 10; trans-Δ2 way that there is a trans double bond in between carbon atom 2 and also 3. Alternatively, the position of a twin bond can be denoted by counting from the distal end, through the ω-carbon atom (the methyl carbon) as number 1. One ω-3 fatty acid, for example, has the structure presented in the margin. Fatty acids room ionized at physiological pH, and also so the is suitable to describe them according to your carboxylate form: because that example, palmitate or hexadecanoate.


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12.2.2. Fatty Acids vary in Chain Length and also Degree the Unsaturation

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


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The properties of fatty acids and also of lipids derived from them room markedly dependent on chain length and also degree the saturation. Unsaturated fatty acids have lower melt points than saturated fatty acids that the exact same length. For example, the melting point of stearic mountain is 69.6°C, whereas the of oleic acid (which consists of one cis dual bond) is 13.4°C. The melt points the polyunsaturated fat acids of the C18 collection are even lower. Chain length additionally affects the melting point, as portrayed by the truth that the melt temperature that palmitic mountain (C16) is 6.5 degrees lower than that the stearic acid (C18). Thus, brief chain length and unsaturation enhance the fluidity of fat acids and of their derivatives.

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