Editing Fatty acid (section)

===Unsaturated fatty acids===
{{main|Unsaturated fat}}
{{Main list|List of unsaturated fatty acids}}
Unsaturated fatty acids have one or more C=C [[double bond]]s. The C=C double bonds can give either [[Cis-trans isomerism|''cis'' or ''trans'']] isomers.

; ''cis'' :A ''cis'' configuration means that the two hydrogen atoms adjacent to the double bond stick out on the same side of the chain. The rigidity of the double bond freezes its conformation and, in the case of the ''cis'' isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the ''cis'' configuration, the less flexibility it has. When a chain has many ''cis'' bonds, it becomes quite curved in its most accessible conformations. For example, [[oleic acid]], with one double bond, has a "kink" in it, whereas [[linoleic acid]], with two double bonds, has a more pronounced bend. [[α-Linolenic acid]], with three double bonds, favors a hooked shape. The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be closely packed, and therefore can affect the melting temperature of the membrane or of the fat. Cis unsaturated fatty acids, however, increase cellular membrane fluidity, whereas trans unsaturated fatty acids do not.
; ''trans'' : A ''trans'' configuration, by contrast, means that the adjacent two hydrogen atoms lie on ''opposite'' sides of the chain. As a result, they do not cause the chain to bend much, and their shape is similar to straight saturated fatty acids.

In most naturally occurring unsaturated fatty acids, each double bond has three ([[omega-3 fatty acid|n−3]]), six ([[omega-6 fatty acid|n−6]]), or nine ([[omega-9 fatty acid|n−9]]) carbon atoms after it, and all double bonds have a cis configuration. Most fatty acids in the ''trans'' configuration ([[trans fat]]s) are not found in nature and are the result of human processing (e.g., [[hydrogenation]]). Some trans fatty acids also occur naturally in the milk and meat of [[ruminant]]s (such as cattle and sheep). They are produced, by fermentation, in the rumen of these animals. They are also found in [[dairy product]]s from milk of ruminants, and may be also found in [[breast milk]] of women who obtained them from their diet.

The geometric differences between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes, and in the construction of biological structures (such as cell membranes).

{| class="wikitable"
|+ Examples of Unsaturated Fatty Acids
|-
! Common name || Chemical structure || Δ{{sup|''x''}}{{efn|Each double bond in the fatty acid is indicated by Δx, where the double bond is located on the xth carbon–carbon bond, counting from the carboxylic acid end.}} || ''C'':''D''{{efn|name=c:d|1="C:D" is the numerical symbol: total amount of (C)arbon atoms of the fatty acid, and the number of (D)ouble (''unsaturated'') bonds in it; if D > 1 it is assumed that the double bonds are separated by one or more [[methylene bridge]](s).}} || IUPAC<ref name="IUPAClipid"/> || ''n''−''x''{{efn|name=omega-x|1=In ''n minus x'' (also ω−x or omega-x) nomenclature a double bond of the fatty acid is located on the xth carbon–carbon bond, counting from the terminal methyl carbon (designated as n or ω) toward the carbonyl carbon.}}
|-
| colspan="6" |'''Omega−3:'''
|-
|[[Eicosapentaenoic acid]]
|CH{{sub|3}}CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|3}}COOH
|''cis'',''cis'',''cis'',''cis'',''cis''-Δ{{sup|5}},Δ{{sup|8}},Δ{{sup|11}},Δ{{sup|14}},Δ{{sup|17}}
|20:5
|20:5(5,8,11,14,17)
|[[omega-3 fatty acid|''n''−3]]
|-
|[[α-Linolenic acid]]
|CH{{sub|3}}CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH
|''cis'',''cis'',''cis''-Δ{{sup|9}},Δ{{sup|12}},Δ{{sup|15}}
|18:3
|18:3(9,12,15)
|[[omega-3 fatty acid|''n''−3]]
|-
|[[Docosahexaenoic acid]]
|CH{{sub|3}}CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|2}}COOH
|''cis'',''cis'',''cis'',''cis'',''cis'',''cis''-Δ{{sup|4}},Δ{{sup|7}},Δ{{sup|10}},Δ{{sup|13}},Δ{{sup|16}},Δ{{sup|19}}
|22:6
|22:6(4,7,10,13,16,19)
|[[omega-3 fatty acid|''n''−3]]
|-
| colspan="6" |'''Omega−6:'''
|-
|[[Arachidonic acid]]
|CH{{sub|3}}(CH{{sub|2}}){{sub|4}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|3}}COOH<sup>[http://webbook.nist.gov/cgi/cbook.cgi?Name=Arachidonic+Acid&Units=SI NIST]</sup>
|''cis'',''cis'',''cis'',''cis''-Δ{{sup|5}}Δ{{sup|8}},Δ{{sup|11}},Δ{{sup|14}}
|20:4
|20:4(5,8,11,14)
|[[omega-6 fatty acid|''n''−6]]
|-
|[[Linoleic acid]]
|CH{{sub|3}}(CH{{sub|2}}){{sub|4}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH
|''cis'',''cis''-Δ{{sup|9}},Δ{{sup|12}}
|18:2
|18:2(9,12)
|[[omega-6 fatty acid|''n''−6]]
|-
|[[Linoelaidic acid]]
|CH{{sub|3}}(CH{{sub|2}}){{sub|4}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH
|''trans'',''trans''-Δ{{sup|9}},Δ{{sup|12}}
|18:2
|18:2(9t,12t)
|[[omega-6 fatty acid|''n''−6]]
|-
| colspan="6" |'''Omega−9:'''
|-
|[[Oleic acid]]|| CH{{sub|3}}(CH{{sub|2}}){{sub|7}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH || ''cis''-Δ{{sup|9}}|| 18:1 || 18:1(9) || [[omega-9 fatty acid|''n''−9]]
|-
|[[Elaidic acid]]|| CH{{sub|3}}(CH{{sub|2}}){{sub|7}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH || ''trans''-Δ{{sup|9}}|| 18:1 || 18:1(9t) || [[omega-9 fatty acid|''n''−9]]
|-
|[[Erucic acid]] || CH{{sub|3}}(CH{{sub|2}}){{sub|7}}'''CH=CH'''(CH{{sub|2}}){{sub|11}}COOH || ''cis''-Δ{{sup|13}}|| 22:1 || 22:1(13) || [[omega-9 fatty acid|''n''−9]]
|-
| colspan="6" |'''Omega−5, 7, and 10:'''
|-
|[[Myristoleic acid]] || CH{{sub|3}}(CH{{sub|2}}){{sub|3}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH || ''cis''-Δ{{sup|9}} || 14:1 || 14:1(9) || ''n''−5
|-
|[[Palmitoleic acid]] || CH{{sub|3}}(CH{{sub|2}}){{sub|5}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH || ''cis''-Δ{{sup|9}} || 16:1 || 16:1(9) || ''n''−7
|-
|[[Vaccenic acid]]
|CH{{sub|3}}(CH{{sub|2}}){{sub|5}}'''CH=CH'''(CH{{sub|2}}){{sub|9}}COOH
|''trans''-Δ{{sup|11}}
|18:1
|18:1(11t)
|''n''−7
|-
|[[Sapienic acid]] || CH{{sub|3}}(CH{{sub|2}}){{sub|8}}'''CH=CH'''(CH{{sub|2}}){{sub|4}}COOH || ''cis''-Δ{{sup|6}} || 16:1 || 16:1(6) || ''n''−10
|}