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{{PsyPerspective}}
 
{{PsyPerspective}}
   
{{Fats}}
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[[Image:Isomers of oleic acid.png|thumb|300px|right|Comparison of the ''trans'' isomer (top) [[Elaidic acid]] and the ''cis''-isomer [[oleic acid]].]]
   
In [[chemistry]], especially [[biochemistry]], a '''fatty acid''' is a [[carboxylic acid]] often with a long unbranched [[aliphatic]] tail ([[Chain (sequence)|chain]]), which is either [[saturation (chemistry)|saturated]] or unsaturated. Carboxylic acids as short as [[butyric acid]] (4 [[carbon]] [[atom]]s) are considered to be fatty acids, while fatty acids derived from natural [[fats]] and [[oils]] may be assumed to have at least 8 carbon atoms, e.g. [[caprylic acid]] (octanoic acid). Most of the natural fatty acids have an even number of carbon atoms, because their [[biosynthesis]] involves [[acetyl-CoA]], a [[coenzyme]] carrying a two-carbon-atom group.
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In [[chemistry]], and especially in [[biochemistry]], a '''fatty acid''' is a [[carboxylic acid]] with a long [[aliphatic]] tail ([[chain]]), which is either [[saturation (chemistry)|saturated]] or [[Unsaturated compound|unsaturated]]. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28.<ref name=iupac>{{cite book| url=http://goldbook.iupac.org/F02330.html |title= IUPAC Compendium of Chemical Terminology|edition= 2nd |year=1997|publisher = International Union of Pure and Applied Chemistry|
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accessdate=2007-10-31| isbn=0-521-51150-X}}</ref> Fatty acids are usually derived from [[triglyceride]]s or [[phospholipid]]s. When they are not attached to other molecules, they are known as "free" fatty acids. Fatty acids are important sources of fuel because, when metabolized, they yield large quantities of [[Adenosine triphosphate|ATP]]. Many cell types can use either [[glucose]] or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids. Despite long-standing assertions to the contrary, the brain can use fatty acids as a source of fuel<ref name="pmid12843297">{{cite journal|last=Ebert|first=D|coauthors=Haller, RG; Walton, ME|title=Energy contribution of octanoate to intact rat brain metabolism measured by 13C nuclear magnetic resonance spectroscopy.|journal=The Journal of neuroscience : the official journal of the Society for Neuroscience|date=2003 Jul 2|volume=23|issue=13|pages=5928–35|url=http://www.jneurosci.org/content/23/13/5928.full|pmid=12843297}}</ref><ref name="pmid23072752">{{cite journal|last=Marin-Valencia|first=Isaac|coauthors=Good, Levi B; Ma, Qian; Malloy, Craig R; Pascual, Juan M|title=Heptanoate as a neural fuel: energetic and neurotransmitter precursors in normal and glucose transporter I-deficient (G1D) brain|journal=Journal of Cerebral Blood Flow & Metabolism|date=17 October 2012|volume=33|issue=2|pages=175–182|doi=10.1038/jcbfm.2012.151|pmid=23072752}}</ref> in addition to glucose and [[ketone bodies]].
Industrially, fatty acids are produced by the [[hydrolysis]] of the [[ester]] linkages in a [[fat]] or biological oil (both of which are [[triglyceride]]s), with the removal of [[glycerol]]. See [[oleochemical]]s.
 
   
 
==Types of fatty acids==
 
==Types of fatty acids==
[[Image:rasyslami.jpg|frame|Several fatty acid molecules]]
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[[Image:rasyslami.jpg|thumb|right|300px|Three-dimensional representations of several fatty acids]]
===Saturated fatty acids===
 
'''Saturated fatty acids''' do not contain any [[double bond]]s or other [[functional group]]s along the chain. The term "saturated" refers to [[hydrogen]], in that all carbons (apart from the carboxylic acid [-COOH] group) contain as many hydrogens as possible. In other words, the omega (ω) end contains 3 hydrogens (CH<sub>3</sub>-) and each carbon within the chain contains 2 hydrogen
 
 
Saturated fatty acids form straight chains and, as a result, can be packed together very tightly, allowing living organisms to store chemical energy very densely. The fatty tissues of animals contain large amounts of long-chain saturated fatty acids. In [[IUPAC nomenclature]], fatty acids have an [-''oic'' acid] suffix. In [[common nomenclature]], the suffix is usually -''ic''.
 
   
The shortest descriptions of fatty acids include only the number of carbon atoms and double bonds in them (e.g. C18:0 or 18:0). [[Stearic acid|C18:0]] means that the carbon chain of the fatty acid consists of 18 carbon atoms and there are no (zero) [[Covalent bond|double bonds]] in it, whereas [[Oleic acid|C18:1]] describes an 18-carbon chain with one [[Covalent bond|double bond]] in it. Each double bond can be either in a [[Geometric isomerism|cis-]] or [[Geometric isomerism|trans-]] conformation and in a different position with respect to the ends of the fatty acid, therefore, not all C18:1s, for example, are identical. If there is one or more double bonds in the fatty acid, it is no longer considered saturated, rather it makes it mono- or polyunsaturated.
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Fatty acids that have [[carbon–carbon double bond]]s are known as unsaturated. Fatty acids without double bonds are known as saturated. They differ in length as well.
   
Most commonly occurring saturated fatty acids are:
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===Length of free fatty acid chains===
[[Image:Dodecanioc_Acid.JPG|thumb|200px|This is a computer generated image of Dodecanoic Acid, a fatty acid.]]
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Fatty acid chains differ by length, often categorized as short to very long.
* [[Butyric acid|Butyric]] (butanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>2</sub>COOH or [[Butyric acid|C4:0]]
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*[[Short-chain fatty acid]]s (SCFA) are fatty acids with [[aliphatic]] tails of fewer than six [[carbon]]s (i.e. [[butyric acid]]).
* [[Caproic acid|Caproic]] (hexanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>COOH or [[Caproic acid|C6:0]]
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*Medium-chain fatty acids (MCFA) are fatty acids with [[aliphatic]] tails of 6–12<ref name=e-medicine>[http://emedicine.medscape.com/article/946755-overview Medscape: Free CME, Medical News, Full-text Journal Articles & More]</ref> [[carbon]]s, which can form [[medium-chain triglyceride]]s.
* [[Caprylic acid|Caprylic]] (octanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>COOH or [[Caprylic acid|C8:0]]
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*Long-chain fatty acids (LCFA) are fatty acids with [[aliphatic]] tails 13 to 21 [[carbon]]s.<ref name=lipidworld>Christopher Beermann1, J Jelinek1, T Reinecker2, A Hauenschild2, G Boehm1, and H-U Klör2, "[http://lipidworld.com/content/2/1/10 Short term effects of dietary medium-chain fatty acids and n-3 long-chain polyunsaturated fatty acids on the fat metabolism of healthy volunteers]"</ref>
* [[Capric acid|Capric]] (decanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>8</sub>COOH or [[Capric acid|C10:0]]
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*[[Very long chain fatty acid]]s (VLCFA) are fatty acids with [[aliphatic]] tails longer than 22 [[carbon]]s
* [[Lauric acid|Lauric]] (dodecanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>10</sub>COOH or [[Lauric acid|C12:0]]
 
* [[Myristic acid|Myristic]] (tetradecanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>12</sub>COOH or [[Myristic acid|C14:0]]
 
* [[Palmitic acid|Palmitic]] (hexadecanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>14</sub>COOH or [[Palmitic acid|C16:0]]
 
* [[Stearic acid|Stearic]] (octadecanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>16</sub>COOH or [[Stearic acid|C18:0]]
 
* [[Arachidic acid|Arachidic]] (eicosanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>18</sub>COOH or [[Arachidic acid|C20:0]]
 
* [[Behenic acid|Behenic]] (docosanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>20</sub>COOH or [[Behenic acid|C22:0]]
 
   
 
===Unsaturated fatty acids===
 
===Unsaturated fatty acids===
'''Unsaturated fatty acids''' are of similar form, except that one or more [[alkenyl]] functional groups exist along the chain, with each alkene substituting a singly-[[chemical bond|bond]]ed " -CH<sub>2</sub>-CH<sub>2</sub>-" part of the chain with a [[Covalent bond|doubly-bonded]] "-CH=CH-" portion (that is, a carbon double bonded to another carbon).
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Unsaturated fatty acids have one or more [[double bond]]s between carbon atoms. (Pairs of carbon atoms connected by double bonds can be saturated by adding hydrogen atoms to them, converting the double bonds to single bonds. Therefore, the double bonds are called unsaturated.)
   
The two next carbon atoms in the chain that are bound to either side of the double bond can occur in a ''[[cis]]'' or ''[[trans]]'' configuration.
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The two carbon atoms in the chain that are bound next to either side of the double bond can occur in a [[Cis-trans isomerism|''cis'' or ''trans'']] configuration.
   
; ''cis'' : A ''cis'' configuration means that the two carbons are on the same side of the double bond. 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, while [[linoleic acid]], with two double bonds, has a more pronounced bend. [[Alpha-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 could affect the melting temperature of the membrane or of the fat.
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; ''cis'' : A ''cis'' configuration means that adjacent hydrogen atoms are on the same side of the double bond. 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. [[Alpha-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 could affect the melting temperature of the membrane or of the fat.
  +
; ''trans'' : A ''trans'' configuration, by contrast, means that the next two hydrogen atoms are bound to ''opposite'' sides of the double bond. As a result, they do not cause the chain to bend much, and their shape is similar to straight saturated fatty acids.
   
; ''trans'' : A ''trans'' configuration, by contrast, means that the next two carbon atoms are bound to ''opposite'' sides of the double bond. As a result, they don't cause the chain to bend much, and their shape is similar to straight saturated fatty acids.
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In most naturally occurring unsaturated fatty acids, each double bond has three ''n'' carbon atoms after it, for some n, and all are cis bonds. 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]]).
   
In most naturally occurring unsaturated fatty acids, each double bond has 3''n'' carbon atoms after it, for some n, and all are cis bonds. Most fatty acids in the ''trans'' configuration (trans fats) are not found in nature and are the result of human processing (eg, [[hydrogenation]]).
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The differences in geometry 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).
   
The differences in geometry between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role is biological processes, and in the construction of biological structures (such as cell membranes).
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{| class="wikitable"
+
|+ Examples of Unsaturated Fatty Acids
====Nomenclature====
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|-
There are two different ways to make clear where the double bonds are located in molecules. For example:
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! Common name || Chemical structure || Δ<sup>''x''</sup> || ''C'':''D'' || ''n''−''x''
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|-
* ''cis''/''trans''-Delta-''x'' or ''cis''/''trans''-Δ<sup>''x''</sup>: The double bond is located on the ''x''th carbon-carbon bond, counting from the carboxyl terminus. The ''cis'' or ''trans'' notation indicates whether the molecule is arranged in a cis or trans conformation. In the case of a molecule having more than one double bond, the notation is, for example, ''cis'',''cis''-Δ<sup>9</sup>,Δ<sup>12</sup>.
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|[[Myristoleic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>3</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH || ''cis''-Δ<sup>9</sup> || 14:1 || ''n''−5
* Omega-''x'' or ω-''x'' : A double bond is located on the ''x''th carbon-carbon bond, counting from the ω, (methyl carbon) end of the chain. Sometimes, the symbol ω is substituted with a lowercase letter ''n'', making it ''n''-6 or ''n''-3.
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|-
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|[[Palmitoleic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>5</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH || ''cis''-Δ<sup>9</sup> || 16:1 || ''n''−7
Examples of unsaturated fatty acids:
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|-
* [[Oleic acid]]: CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH or ''cis''-Δ<sup>9</sup> [[Oleic acid|C18:1]]
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|[[Sapienic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>8</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>4</sub>COOH || ''cis''-Δ<sup>6</sup> || 16:1 || ''n''−10
* [[Linoleic acid]]: CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH or [[Linoleic acid|C18:2]]
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|-
* [[Alpha-linolenic acid]]: CH<sub>3</sub>CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH or [[Alpha-linolenic acid|C18:3]]
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|[[Oleic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH || ''cis''-Δ<sup>9</sup> || 18:1 || [[omega-9 fatty acid|''n''−9]]
* [[Arachidonic acid]] CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>3</sub>COOH<sup>[http://webbook.nist.gov/cgi/cbook.cgi?Name=Arachidonic+Acid&Units=SI NIST]</sup> or [[Arachidonic acid|C20:4]]
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|-
* [[Eicosapentaenoic acid]] or [[Eicosapentaenoic acid|C20:5]]
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|[[Elaidic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH || ''trans''-Δ<sup>9</sup> || 18:1 || [[omega-9 fatty acid|''n''−9]]
* [[Docosahexaenoic acid]] or [[Docosahexaenoic acid|C22:6]]
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|-
* [[Erucic acid]]: CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>11</sub>COOH or [[Erucic acid|C22:1]]
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|[[Vaccenic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>5</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>9</sub>COOH || ''trans''-Δ<sup>11</sup> || 18:1 || ''n''−7
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|-
Alpha-linolenic, docosahexaenoic, and eicosapentaenoic acids are examples of [[omega-3 fatty acid]]s. Linoleic acid and arachidonic acid are [[omega-6 fatty acid]]s. Oleic and erucic acid are [[omega-9 fatty acid]]s. Stearic and oleic acid are both 18 [[Carbon|C]] fatty acids. They differ only in that stearic acid is saturated with hydrogen, while oleic acid is an unsaturated fatty acid with two fewer hydrogens.
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|[[Linoleic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH || ''cis'',''cis''-Δ<sup>9</sup>,Δ<sup>12</sup> || 18:2 || [[omega-6 fatty acid|''n''−6]]
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|-
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|[[Linoelaidic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH || ''trans'',''trans''-Δ<sup>9</sup>,Δ<sup>12</sup> || 18:2 || [[omega-6 fatty acid|''n''−6]]
  +
|-
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|[[Alpha-linolenic acid|α-Linolenic acid]] || CH<sub>3</sub>CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH || ''cis'',''cis'',''cis''-Δ<sup>9</sup>,Δ<sup>12</sup>,Δ<sup>15</sup> || 18:3 || [[omega-3 fatty acid|''n''−3]]
  +
|-
  +
|[[Arachidonic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>3</sub>COOH<sup>[http://webbook.nist.gov/cgi/cbook.cgi?Name=Arachidonic+Acid&Units=SI NIST]</sup> || ''cis'',''cis'',''cis'',''cis''-Δ<sup>5</sup>Δ<sup>8</sup>,Δ<sup>11</sup>,Δ<sup>14</sup> || 20:4 || [[omega-6 fatty acid|''n''−6]]
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|-
  +
|[[Eicosapentaenoic acid]] || CH<sub>3</sub>CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>3</sub>COOH || ''cis'',''cis'',''cis'',''cis'',''cis''-Δ<sup>5</sup>,Δ<sup>8</sup>,Δ<sup>11</sup>,Δ<sup>14</sup>,Δ<sup>17</sup> || 20:5 || [[omega-3 fatty acid|''n''−3]]
  +
|-
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|[[Erucic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>11</sub>COOH || ''cis''-Δ<sup>13</sup> || 22:1 || [[omega-9 fatty acid|''n''−9]]
  +
|-
  +
|[[Docosahexaenoic acid]] || CH<sub>3</sub>CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''CH<sub>2</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>2</sub>COOH || ''cis'',''cis'',''cis'',''cis'',''cis'',''cis''-Δ<sup>4</sup>,Δ<sup>7</sup>,Δ<sup>10</sup>,Δ<sup>13</sup>,Δ<sup>16</sup>,Δ<sup>19</sup> || 22:6 || [[omega-3 fatty acid|''n''−3]]
  +
|}
   
 
====Essential fatty acids====
 
====Essential fatty acids====
{{main|Essential fatty acid}}
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{{Main|Essential fatty acid}}
  +
Fatty acids that are required by the human body but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids. There are two series of essential fatty acids: one has a double bond [[Omega-3 fatty acid|three carbon atoms]] removed from the methyl end; the other has a double bond [[Omega-6 fatty acid|six carbon atoms]] removed from the methyl end. Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side.<ref>[http://books.google.com/books?id=3a6p9pA5gZ8C&pg=PA42 Cell Biology: A Short Course]</ref> Two essential fatty acids are [[linoleic acid]] (LA) and [[alpha-linolenic acid]] (ALA). They are widely distributed in plant oils. The human body has a limited ability to convert ALA into the longer-chain ''n''-3 fatty acids [[eicosapentaenoic acid]] (EPA) and [[docosahexaenoic acid]] (DHA), which can also be obtained from fish.
   
The human body can produce all but two of the fatty acids it needs. These two, linoleic acid and [[alpha-linolenic acid]], are widely distributed in plant and fish oils. Since they cannot be made in the body from other substrates and must be supplied in food, they are called essential fatty acids. In the body, essential fatty acids are primarily used to produce hormone-like substances that regulate a wide range of functions, including blood pressure, blood clotting, blood lipid levels, the immune response, and the inflammation response to injury infection.
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===Saturated fatty acids===
  +
{{Main|Saturated fat}}
  +
{{Main list|List of saturated fatty acids}}
   
Essential fatty acids are polyunsaturated fatty acids and are the parent compounds of the omega-6 and omega-3 fatty acid series, respectively. They are essential in the human diet because there is no synthetic mechanism for them. Humans can easily make saturated fatty acids or monounsaturated fatty acids with a double bond at the omega-9 position, but do not have the enzymes necessary to introduce a double bond at the omega-3 or omega-6 position.
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Saturated fatty acids are long-chain carboxylic acids that usually have between 12 and 24 carbon atoms and have no double bonds. Thus, saturated fatty acids are saturated with hydrogen (since double bonds reduce the number of hydrogens on each carbon). Because saturated fatty acids have only single bonds, each carbon atom within the chain has 2 hydrogen atoms (except for the omega carbon at the end that has 3 hydrogens).
   
The essential fatty acids are important in several human body systems, including the immune system and in blood pressure regulation, since they are used to make compounds such as [[prostaglandin]]s. The brain has increased amounts of linolenic and alpha-linoleic acid derivatives. Changes in the levels and balance of these fatty acids due to a typical Western diet rich in omega-6 and poor in omega-3 fatty acids is alleged to be associated with [[Depression (mood)|depression]] and behavioral change, including violence. The actual connection, if any, is still under investigation. Further, changing to a more natural diet, or consumption of supplements to compensate for a dietary imbalance, has been associated with reduced violent behavior<ref name="prison">{{cite journal
+
[[File:Arachidic formula representation.svg|thumb|300px|Arachidic acid, a saturated fatty acid.]]
| author = C. Bernard Gesch, CQSW Sean M. Hammond, PhD Sarah E. Hampson, PhD Anita Eves, PhD Martin J. Crowder, PhD
 
| year = 2002
 
| title = Influence of supplementary vitamins, minerals and essential fatty acids on the antisocial behaviour of young adult prisoners
 
| journal = The British Journal of Psychiatry
 
| volume = 181
 
| pages = 22-28
 
| url = http://bjp.rcpsych.org/cgi/content/full/181/1/22
 
| accessdate = 2006-06-27
 
}} </ref> and increased attention span, but the mechanisms for the effect are still unclear. So far, at least three human studies have shown results that support this: two school studies{{citeneeded}}<ref>{{cite journal
 
| author = Alexandra J. Richardson and Paul Montgomery
 
| year = 2005
 
| title = The Oxford-Durham study: a randomized controlled trial of dietary supplementation with fatty acids in children with developmental coordination disorder
 
| journal = Pediatrics
 
| volume = 115
 
| issue = 5
 
| pages = 1360 - 1366
 
| doi = 10.1542/peds.2004-2164
 
| accessdate = 2006-06-27
 
}} </ref> as well as a double blind study in a prison.<ref name="prison" /><ref>{{cite book | first = Felicity | last = Lawrence | year = 2004 | title = Not on the Label | editor = Kate Barker | pages = 213 | publisher = Penguin | id = ISBN 0-141-01566-7 }}</ref><ref>{{cite web | title = Using Fatty Acids for Enhancing Classroom Achievement | url = http://www.durhamtrial.org/ | accessmonthday = January | accessyear = 2004 }}</ref>
 
   
====Trans fatty acids====
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{| class="wikitable"
{{main|Trans fat}}
+
|+ Examples of Saturated Fatty Acids
  +
|-
  +
! Common name || Chemical structure || ''C'':''D''
  +
|-
  +
| [[Caprylic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>COOH || 8:0
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|-
  +
| [[Capric acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>8</sub>COOH || 10:0
  +
|-
  +
| [[Lauric acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>10</sub>COOH || 12:0
  +
|-
  +
| [[Myristic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>12</sub>COOH || 14:0
  +
|-
  +
| [[Palmitic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>14</sub>COOH || 16:0
  +
|-
  +
| [[Stearic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>16</sub>COOH || 18:0
  +
|-
  +
| [[Arachidic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>18</sub>COOH || 20:0
  +
|-
  +
| [[Behenic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>20</sub>COOH || 22:0
  +
|-
  +
| [[Lignoceric acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>22</sub>COOH || 24:0
  +
|-
  +
| [[Cerotic acid]] || CH<sub>3</sub>(CH<sub>2</sub>)<sub>24</sub>COOH || 26:0
  +
|}
   
A '''trans fatty acid''' (commonly shortened to '''trans fat''') is an unsaturated fatty acid molecule that contains a ''trans'' double bond between [[carbon]] atoms, which makes the molecule less 'kinked' in comparison to fatty acids with ''cis'' double bonds. These bonds are characteristically produced during industrial hydrogenation of plant oils. Research suggests that increasing amounts of trans fats are, for causal reasons not well understood, correlate with circulatory diseases such as [[atherosclerosis]] and [[coronary heart disease]], than the same amount of non-trans fats.
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==Nomenclature==
  +
[[File:Fatty acid numbering.png|thumb|upright=2|Numbering of carbon atoms]]
   
==Free fatty acids==
+
Several different systems of nomenclature are used for fatty acids. The following table describes the most common systems.
Fatty acids can be bound or attached to other molecules, such as in triglycerides or [[phospholipid]]s. When they are not attached to other molecules, they are known as "free" fatty acids.
+
{{Clear}}
  +
{| class="wikitable"
  +
|-
  +
!System
  +
!Example
  +
!Explanation
  +
|-
  +
!Trivial nomenclature
  +
|[[Palmitoleic acid]]
  +
|'''[[Trivial name]]s''' (or '''common names''') are non-systematic historical names, which are the most frequent naming system used in literature. Most common fatty acids have trivial names in addition to their ''systematic names'' (see below). These names frequently do not follow any pattern, but they are concise and often unambiguous.
  +
|-
  +
!Systematic nomenclature
  +
|[[Oleic acid|(9Z)-octadecenoic acid]]
  +
|'''[[Systematic name]]s''' (or '''IUPAC names''') derive from the standard ''[[IUPAC nomenclature of organic chemistry|IUPAC Rules for the Nomenclature of Organic Chemistry]]'', published in 1979,<ref name="nomenclature-1979">{{cite book |title=Nomenclature of Organic Chemistry |author=Rigaudy, J. |coauthors=Klesney, S.P. |publisher=[[Pergamon]] |year=1979 |isbn=0-08-022369-9 |oclc=5008199}}</ref> along with a recommendation published specifically for lipids in 1977.<ref name="nomenclature-1977">{{cite journal |year=1977 |title=The Nomenclature of Lipids. Recommendations, 1976 |volume=79 |issue=1 |pages=11–21 |doi=10.1111/j.1432-1033.1977.tb11778.x |url=http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1432-1033.1977.tb11778.x |journal=[[European Journal of Biochemistry]]}}</ref> Counting begins from the [[carboxylic acid]] end. [[Double bond]]s are labelled with ''[[cis-trans isomerism|cis]]''-/''[[cis-trans isomerism|trans]]''- notation or ''[[E-Z notation|E]]''-/''[[E-Z notation|Z]]''- notation, where appropriate. This notation is generally more verbose than common nomenclature, but has the advantage of being more technically clear and descriptive.
  +
|-
  +
!Δ<sup>''x''</sup> nomenclature
  +
|[[Linoleic acid|''cis'',''cis''-Δ<sup>9</sup>,Δ<sup>12</sup> octadecadienoic acid]]
  +
|In '''Δ<sup>''x''</sup>''' (or '''delta-''x''''') '''nomenclature''', each double bond is indicated by Δ<sup>''x''</sup>, where the double bond is located on the ''x''th carbon–carbon bond, counting from the carboxylic acid end. Each double bond is preceded by a ''[[cis-trans isomerism|cis]]''- or ''[[cis-trans isomerism|trans]]''- prefix, indicating the conformation of the molecule around the bond. For example, [[linoleic acid]] is designated "cis-Δ<sup>9</sup>, cis-Δ<sup>12</sup> octadecadienoic acid". This nomenclature has the advantage of being less verbose than systematic nomenclature, but is no more technically clear or descriptive.
  +
|-
  +
!''n''−''x'' nomenclature
  +
|[[Omega-3 fatty acid|''n''−3]]
  +
|'''''n''−''x''''' ('''''n'' minus ''x'''''; also '''ω−''x''''' or '''omega-''x''''') '''nomenclature''' both provides names for individual compounds and classifies them by their likely biosynthetic properties in animals. A double bond is located on the ''x''<sup>th</sup> carbon–carbon bond, counting from the terminal [[methyl]] carbon (designated as ''n'' or ω) toward the [[carbonyl]] carbon. For example, [[alpha-linolenic acid|α-Linolenic acid]] is classified as a [[omega-3 fatty acid|''n''−3]] or [[omega-3]] fatty acid, and so it is likely to share a biosynthetic pathway with other compounds of this type. The ω−''x'', omega-''x'', or "omega" notation is common in popular nutritional literature, but [[IUPAC nomenclature|IUPAC]] has deprecated it in favor of ''n''−''x'' notation in technical documents.<ref name="nomenclature-1979" /> The most commonly researched fatty acid biosynthetic pathways are [[omega-3 fatty acid|''n''−3]] and [[omega-6 fatty acid|''n''−6]], which are hypothesized{{By whom|date=November 2010}} to decrease or increase, respectively,{{Citation needed|date=November 2010}} inflammation.
  +
|-
  +
!Lipid numbers
  +
|18:3<br />[[Gamma-linolenic acid|18:3ω6]]<br />[[Alpha-linolenic acid|18:3,&nbsp;cis,cis,cis-Δ<sup>9</sup>,Δ<sup>12</sup>,Δ<sup>15</sup>]]<br />
  +
|'''Lipid numbers''' take the form ''C'':''D'', where ''C'' is the number of carbon atoms in the fatty acid and ''D'' is the number of double bonds in the fatty acid (if more than one, the double bonds are assumed to be interrupted by [[methylene bridge|{{chem|CH|2}} units]], ''i.e.'', at intervals of 3 carbon atoms along the chain). This notation can be ambiguous, as some different fatty acids can have the same numbers. Consequently, when ambiguity exists this notation is usually paired with either a Δ<sup>''x''</sup> or ''n''−''x'' term.<ref name="nomenclature-1979" />
  +
|}
   
The '''uncombined fatty acids''' or '''free fatty acids''' may come from the breakdown of a triglyceride into its components (fatty acids and glycerol).
+
==Production==
  +
Fatty acids are usually produced industrially by the [[hydrolysis]] of [[triglyceride]]s, with the removal of [[glycerol]] (see [[oleochemical]]s). [[Phospholipid]]s represent another source. Some fatty acids are produced synthetically by [[carbonylation|hydrocarboxylation]] of alkenes.
   
Free fatty acids are an important source of fuel for many tissues since they can yield relatively large quantities of [[Adenosine triphosphate|ATP]]. Many cell types can use either [[glucose]] or fatty acids for this purpose. However, heart and skeletal muscle prefer fatty acids. On the other hand, the brain cannot use fatty acids as a source of fuel, relying instead on glucose, or on [[ketone bodies]] produced by the liver from [[fatty acid metabolism]] during starvation, or periods of low carbohydrate intake.
+
===Free fatty acids===
  +
{{main|fatty acid synthesis}}
  +
The [[biosynthesis]] of fatty acids involves the condensation of [[acetyl-CoA]]. Since this [[coenzyme]] carries a two-carbon-atom group, almost all natural fatty acids have even numbers of carbon atoms.
   
== Fatty acids in dietary fats ==
+
The "uncombined fatty acids" or "free fatty acids" found in organisms come from the breakdown of a triglyceride{{citation needed|reason=The previous sentence says it comes from condensation with acetyl-CoA"|date=January 2011}}. Because they are insoluble in water, these fatty acids are transported (solubilized, circulated) while bound to plasma [[protein albumin]]. The levels of "free fatty acid" in the blood are limited by the availability of albumin binding sites.
   
The following table gives the fatty acid and cholesterol composition of some common dietary fats.<ref>
+
== Fatty acids in dietary fats ==
  +
The following table gives the fatty acid, vitamin E and cholesterol composition of some common dietary fats.<ref>
 
{{cite book
 
{{cite book
| title=McCance & Widdowson's The Composition of Foods
+
| title=McCance & Widdowson's the Composition of Foods
 
| chapter=Fats and Oils
 
| chapter=Fats and Oils
 
| author=Food Standards Agency
 
| author=Food Standards Agency
Line 86: Line 86:
 
| author=Ted Altar
 
| author=Ted Altar
 
| accessdate=2006-08-31
 
| accessdate=2006-08-31
| publisher=Sundance Natural Foods Online
+
| publisher=[[Sundance Natural Foods]] Online
 
}}
 
}}
 
</ref>
 
</ref>
   
 
{| class="wikitable" |
 
{| class="wikitable" |
|+
+
|+
 
! !! Saturated !! Monounsaturated !! Polyunsaturated !! Cholesterol !! Vitamin E
 
! !! Saturated !! Monounsaturated !! Polyunsaturated !! Cholesterol !! Vitamin E
 
|-
 
|-
Line 99: Line 99:
 
|-
 
|-
 
| [[Lard]] || align="right" | 40.8 || align="right" | 43.8 || align="right" | 9.6 || align="right" | 93 || align="right" | 0.00
 
| [[Lard]] || align="right" | 40.8 || align="right" | 43.8 || align="right" | 9.6 || align="right" | 93 || align="right" | 0.00
  +
|-
  +
| [[Duck fat]]<ref>
  +
{{cite web
  +
| url=http://www.nal.usda.gov/fnic/foodcomp/search/
  +
| title=USDA National Nutrient Database for Standard Reference
  +
| author=U. S. Department of Agriculture.
  +
| accessdate=2010-02-17
  +
| publisher=U. S. Department of Agriculture.
  +
}}
  +
</ref> || align="right" | 33.2 || align="right" | 49.3 || align="right" | 12.9 || align="right" | 100 || align="right" | 2.70
 
|-
 
|-
 
| [[Butter]] || align="right" | 54.0 || align="right" | 19.8 || align="right" | 2.6 || align="right" | 230 || align="right" | 2.00
 
| [[Butter]] || align="right" | 54.0 || align="right" | 19.8 || align="right" | 2.6 || align="right" | 230 || align="right" | 2.00
Line 105: Line 115:
 
|-
 
|-
 
| [[Coconut oil]] || align="right" | 85.2 || align="right" | 6.6 || align="right" | 1.7 || align="right" | 0 || align="right" | .66
 
| [[Coconut oil]] || align="right" | 85.2 || align="right" | 6.6 || align="right" | 1.7 || align="right" | 0 || align="right" | .66
  +
|-
  +
| [[Palm kernel oil]] || align="right" | 81.5 || align="right" | 11.4 || align="right" | 1.6 || align="right" | 0 || align="right" | 3.80
 
|-
 
|-
 
| [[Palm oil]] || align="right" | 45.3 || align="right" | 41.6 || align="right" | 8.3 || align="right" | 0 || align="right" | 33.12
 
| [[Palm oil]] || align="right" | 45.3 || align="right" | 41.6 || align="right" | 8.3 || align="right" | 0 || align="right" | 33.12
Line 118: Line 130:
 
| [[Corn oil]] || align="right" | 12.7 || align="right" | 24.7 || align="right" | 57.8 || align="right" | 0 || align="right" | 17.24
 
| [[Corn oil]] || align="right" | 12.7 || align="right" | 24.7 || align="right" | 57.8 || align="right" | 0 || align="right" | 17.24
 
|-
 
|-
| [[Sunflower oil]] || align="right" | 11.9 || align="right" | 20.2 || align="right" | 63.0 || align="right" | 0 || align="right" | 49.0&nbsp;
+
| [[Sunflower oil]] || align="right" | 11.9 || align="right" | 20.2 || align="right" | 63.0 || align="right" | 0 || align="right" | 49.00
 
|-
 
|-
 
| [[Safflower oil]] || align="right" | 10.2 || align="right" | 12.6 || align="right" | 72.1 || align="right" | 0 || align="right" | 40.68
 
| [[Safflower oil]] || align="right" | 10.2 || align="right" | 12.6 || align="right" | 72.1 || align="right" | 0 || align="right" | 40.68
 
|-
 
|-
| [[Rapeseed oil]] || align="right" | 5.3 || align="right" | 64.3 || align="right" | 24.8 || align="right" | 0 || align="right" | 22.21
+
| [[Hemp oil]] || align="right" | 10 || align="right" | 15 || align="right" | 75 || align="right" | 0 || align="right" |
  +
|-
  +
| [[Canola|Canola/Rapeseed oil]] || align="right" | 5.3 || align="right" | 64.3 || align="right" | 24.8 || align="right" | 0 || align="right" | 22.21
 
|}
 
|}
   
==Acidity==
+
==Reactions of fatty acids==
Short chain carboxylic acids such as [[formic acid]] and [[acetic acid]] are miscible with water and dissociate to form reasonably strong acids ([[acid dissociation constant|pK<sub>a</sub>]] 3.77 and 4.76, respectively). Longer chain fatty acids do not show a great change in pK<sub>a</sub>. [[Nonanoic acid]], for example, has a pK<sub>a</sub> of 4.96. However, as the chain length increases the solubility of the fatty acids in water decreases very rapidly, so that the longer chain fatty acids have very little effect on the [[pH]] of a solution. The significance of their pK<sub>a</sub> values therefore only has relevance to the types of reactions in which they can take part.
+
Fatty acids exhibit reactions like other carboxylic acids, i.e. they undergo [[esterification]] and acid-base reactions.
   
Even those fatty acids that are insoluble in water will dissolve in warm [[ethanol]], and can be [[titration|titrated]] with [[sodium hydroxide]] solution using [[phenolphthalein]] as an indicator to a pale pink endpoint. This analysis is used to determine the free fatty acid content of fats, i.e. the proportion of the triglycerides that have been hydrolyzed.
+
===Acidity===
  +
Fatty acids do not show a great variation in their acidities, as indicated by their respective pK<sub>a</sub>. [[Nonanoic acid]], for example, has a pK<sub>a</sub> of 4.96, being only slightly weaker than acetic acid (4.76). As the chain length increases, the solubility of the fatty acids in water decreases very rapidly, so that the longer-chain fatty acids have minimal effect on the [[pH]] of an aqueous solution. Even those fatty acids that are insoluble in water will dissolve in warm [[ethanol]], and can be [[titration|titrated]] with [[sodium hydroxide]] solution using [[phenolphthalein]] as an indicator to a pale-pink endpoint. This analysis is used to determine the free fatty acid content of fats; i.e., the proportion of the triglycerides that have been [[hydrolysis|hydrolyze]]d.
   
==Reaction of fatty acids==
+
===Hydrogenation and hardening===
  +
[[Hydrogenation]] of unsaturated fatty acids is widely practiced to give saturated fatty acids, which are less prone toward [[rancidification]]. Since the saturated fatty acids are higher melting than the unsaturated relatives, the process is called hardening. This technology is used to convert vegetable oils into [[margarine]]. During partial hydrogenation, unsaturated fatty acids can be isomerized from ''cis'' to ''trans'' configuration.<ref name=Ullmann>David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. {{DOI|10.1002/14356007.a10_245.pub2}}</ref>
   
Fatty acids react just like any other carboxylic acid, which means they can undergo [[esterification]] and acid-base reactions. [[Reduction (chemistry)|Reduction]] of fatty acids yields [[fatty alcohol]]s. Unsaturated fatty acids can additionally undergo addition reactions, most commonly [[hydrogenation]], which is used to convert vegetable oils into margarine. With partial hydrogenation, unsaturated fatty acids can be isomerized from ''cis'' to ''trans'' configuration.
+
More forcing hydrogenation, i.e. using higher pressures of H<sub>2</sub> and higher temperatures, converts fatty acids into [[fatty alcohol]]s. Fatty alcohols are, however, more easily produced from fatty acid [[ester]]s.
  +
  +
In the [[Varrentrapp reaction]] certain unsaturated fatty acids are cleaved in molten alkali, a reaction at one time of relevance to structure elucidation.
   
 
===Auto-oxidation and rancidity===
 
===Auto-oxidation and rancidity===
{{main|Rancidification}}
+
{{Main|Rancidification}}
  +
Unsaturated fatty acids undergo a chemical change known as [[auto-oxidation]]. The process requires oxygen (air) and is accelerated by the presence of trace metals. Vegetable oils resist this process because they contain antioxidants, such as [[tocopherol]]. Fats and oils often are treated with [[chelation|chelating agents]] such as [[citric acid]] to remove the metal catalysts.
   
Fatty acids at room temperature undergo a chemical change known as [[auto-oxidation]]. The fatty acid breaks down into [[hydrocarbon]]s, [[ketone]]s, [[aldehyde]]s, and smaller amounts of [[epoxide]]s and [[alcohol]]s. Heavy metals present at low levels in fats and oils promote auto-oxidation. Fats and oils often are treated with [[chelation|chelating agents]] such as [[citric acid]].
+
===Ozonolysis===
  +
Unsaturated fatty acids are susceptible to degradation by ozone. This reaction is practiced in the production of [[azelaic acid]] ((CH<sub>2</sub>)<sub>7</sub>(CO<sub>2</sub>H)<sub>2</sub>) from [[oleic acid]].<ref name=Ullmann/>
   
==Sources==
+
===Analysis===
<references />
+
In chemical analysis, fatty acids are separated by gas chromatography of methyl esters; additionally, a separation of unsaturated isomers is possible by argentation thin-layer chromatography.<ref> B. Breuer, T. Stuhlfauth et H. P. Fock, Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography, J. of Chromatogr. Science 25 (1987), S. 302-306 [http://chromsci.oxfordjournals.org/content/25/7/302.abstract]</ref>
  +
  +
==Circulation==
  +
===Digestion and intake===
  +
{{Main|Digestion#Fat digestion}}
  +
[[Short-chain fatty acid|Short-]] and medium-chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the [[portal vein]] just as other absorbed nutrients do. However, [[long-chain fatty acids]] are not directly released into the intestinal capillaries. Instead they are absorbed into the fatty walls of the intestine [[Intestinal villus|villi]] and reassembled again into [[triglycerides]]. The triglycerides are coated with [[cholesterol]] and protein (protein coat) into a compound called a [[chylomicron]].
  +
  +
Within the villi, the chylomicron enters a [[lymphatic]] capillary called a [[lacteal]], which merges into larger lymphatic vessels. It is transported via the lymphatic system and the [[thoracic duct]] up to a location near the heart (where the arteries and veins are larger). The thoracic duct empties the chylomicrons into the bloodstream via the left [[subclavian vein]]. At this point the chylomicrons can transport the triglycerides to tissues where they are stored or metabolized for energy.
  +
  +
===Metabolism===
  +
{{Main|Fatty acid metabolism}}
  +
Fatty acids (provided either by ingestion or by drawing on triglycerides stored in fatty tissues) are distributed to cells to serve as a fuel for muscular contraction and general metabolism. They are consumed by [[mitochondria]] to produce [[Adenosine triphosphate|ATP]] through [[beta oxidation]].
  +
  +
===Distribution===
  +
{{Main|Blood fatty acids}}
  +
Blood fatty acids are in different forms in different stages in the blood circulation. They are taken in through the intestine in [[chylomicrons]], but also exist in [[very low density lipoprotein]]s (VLDL) and [[low density lipoprotein]]s (LDL) after processing in the liver. In addition, when released from [[adipocytes]], fatty acids exist in the blood as [[free fatty acids]].
  +
  +
It is proposed that the blend of fatty acids exuded by mammalian skin, together with [[lactic acid]] and [[pyruvic acid]], is distinctive and enables animals with a keen sense of smell to differentiate individuals.<ref>{{cite news
  +
| url=http://www.sciencedaily.com/releases/2009/07/090721091839.htm
  +
| title=Electronic Nose Created To Detect Skin Vapors
  +
| date=July 21, 2009
  +
| publisher=Science Daily
  +
| accessdate=2010-05-18
  +
}}</ref>
   
 
==See also==
 
==See also==
 
{{Commons|Fatty acids}}
 
{{Commons|Fatty acids}}
* [[Capsaicin]]
+
*[[Essential fatty acid]]
* [[Essential fatty acid]]
+
*[[Fatty acid metabolism]]
* [[Phosphatides]]
+
*[[Fatty acid synthase]]
* [[Prostoglandins]]
+
*[[Fatty acid synthesis]]
* [[Triglyceride]]
+
*[[Fatty aldehyde]]
* [[Saturated fat]]
+
*[[List of saturated fatty acids]]
* [[Unsaturated fat]]
+
*[[Saturated fat]]
* [[Fatty acid metabolism]]
+
*[[Unsaturated fat]]
  +
  +
  +
==References==
  +
{{Reflist|2}}
   
 
==External links==
 
==External links==
* [http://www.scientificpsychic.com/fitness/fattyacids.html Chemical Structure of Fats and Fatty Acids]
+
*[http://www.lipidlibrary.co.uk/ Lipid Library]
* [http://www.cyberlipid.org/glycer/glyc0005.htm Plant Oils and Fats], from the [http://www.cyberlipid.org/ Cyberlipid Center Web site]
+
*[http://intl.elsevierhealth.com/journals/plef/ ''Prostaglandins, Leukotrienes & Essential Fatty Acids'' Journal]
* {{cite web
+
*[http://www.dmfpolska.eu/Diagnostics.html Fatty Blood Acids ]
| url=http://www.curezone.com/foods/fatspercent.asp
+
| title=Fat content and fatty acid composition of seed oils
+
{{Fatty acids}}
| accessdate=2006-10-07
 
}} From Udo Erasmus' book, [http://www.curezone.com/books/best/book.asp?ID=103 Fats that Heal Fats that Kill]
 
   
[[Category:Acids]]
+
{{DEFAULTSORT:Fatty Acid}}
 
[[Category:Fatty acids|*]]
 
[[Category:Fatty acids|*]]
[[Category:Lipids]]
 
 
[[Category:Nutrition]]
 
[[Category:Nutrition]]
   
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File:Isomers of oleic acid.png

In chemistry, and especially in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic tail (chain), which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28.[1] Fatty acids are usually derived from triglycerides or phospholipids. When they are not attached to other molecules, they are known as "free" fatty acids. Fatty acids are important sources of fuel because, when metabolized, they yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids. Despite long-standing assertions to the contrary, the brain can use fatty acids as a source of fuel[2][3] in addition to glucose and ketone bodies.

Types of fatty acidsEdit

Rasyslami

Three-dimensional representations of several fatty acids

Fatty acids that have carbon–carbon double bonds are known as unsaturated. Fatty acids without double bonds are known as saturated. They differ in length as well.

Length of free fatty acid chainsEdit

Fatty acid chains differ by length, often categorized as short to very long.

Unsaturated fatty acidsEdit

Unsaturated fatty acids have one or more double bonds between carbon atoms. (Pairs of carbon atoms connected by double bonds can be saturated by adding hydrogen atoms to them, converting the double bonds to single bonds. Therefore, the double bonds are called unsaturated.)

The two carbon atoms in the chain that are bound next to either side of the double bond can occur in a cis or trans configuration.

cis 
A cis configuration means that adjacent hydrogen atoms are on the same side of the double bond. 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. Alpha-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 could affect the melting temperature of the membrane or of the fat.
trans 
A trans configuration, by contrast, means that the next two hydrogen atoms are bound to opposite sides of the double bond. 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 n carbon atoms after it, for some n, and all are cis bonds. Most fatty acids in the trans configuration (trans fats) are not found in nature and are the result of human processing (e.g., hydrogenation).

The differences in geometry 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).

Examples of Unsaturated Fatty Acids
Common name Chemical structure Δx C:D nx
Myristoleic acid CH3(CH2)3CH=CH(CH2)7COOH cis9 14:1 n−5
Palmitoleic acid CH3(CH2)5CH=CH(CH2)7COOH cis9 16:1 n−7
Sapienic acid CH3(CH2)8CH=CH(CH2)4COOH cis6 16:1 n−10
Oleic acid CH3(CH2)7CH=CH(CH2)7COOH cis9 18:1 n−9
Elaidic acid CH3(CH2)7CH=CH(CH2)7COOH trans9 18:1 n−9
Vaccenic acid CH3(CH2)5CH=CH(CH2)9COOH trans11 18:1 n−7
Linoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH cis,cis912 18:2 n−6
Linoelaidic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH trans,trans912 18:2 n−6
α-Linolenic acid CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH cis,cis,cis91215 18:3 n−3
Arachidonic acid CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOHNIST cis,cis,cis,cis5Δ81114 20:4 n−6
Eicosapentaenoic acid CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH cis,cis,cis,cis,cis58111417 20:5 n−3
Erucic acid CH3(CH2)7CH=CH(CH2)11COOH cis13 22:1 n−9
Docosahexaenoic acid CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)2COOH cis,cis,cis,cis,cis,cis4710131619 22:6 n−3

Essential fatty acidsEdit

Main article: Essential fatty acid

Fatty acids that are required by the human body but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids. There are two series of essential fatty acids: one has a double bond three carbon atoms removed from the methyl end; the other has a double bond six carbon atoms removed from the methyl end. Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side.[6] Two essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA). They are widely distributed in plant oils. The human body has a limited ability to convert ALA into the longer-chain n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which can also be obtained from fish.

Saturated fatty acidsEdit

Main article: Saturated fat

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Saturated fatty acids are long-chain carboxylic acids that usually have between 12 and 24 carbon atoms and have no double bonds. Thus, saturated fatty acids are saturated with hydrogen (since double bonds reduce the number of hydrogens on each carbon). Because saturated fatty acids have only single bonds, each carbon atom within the chain has 2 hydrogen atoms (except for the omega carbon at the end that has 3 hydrogens).

File:Arachidic formula representation.svg
Examples of Saturated Fatty Acids
Common name Chemical structure C:D
Caprylic acid CH3(CH2)6COOH 8:0
Capric acid CH3(CH2)8COOH 10:0
Lauric acid CH3(CH2)10COOH 12:0
Myristic acid CH3(CH2)12COOH 14:0
Palmitic acid CH3(CH2)14COOH 16:0
Stearic acid CH3(CH2)16COOH 18:0
Arachidic acid CH3(CH2)18COOH 20:0
Behenic acid CH3(CH2)20COOH 22:0
Lignoceric acid CH3(CH2)22COOH 24:0
Cerotic acid CH3(CH2)24COOH 26:0

NomenclatureEdit

File:Fatty acid numbering.png

Several different systems of nomenclature are used for fatty acids. The following table describes the most common systems.

System Example Explanation
Trivial nomenclature Palmitoleic acid Trivial names (or common names) are non-systematic historical names, which are the most frequent naming system used in literature. Most common fatty acids have trivial names in addition to their systematic names (see below). These names frequently do not follow any pattern, but they are concise and often unambiguous.
Systematic nomenclature (9Z)-octadecenoic acid Systematic names (or IUPAC names) derive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry, published in 1979,[7] along with a recommendation published specifically for lipids in 1977.[8] Counting begins from the carboxylic acid end. Double bonds are labelled with cis-/trans- notation or E-/Z- notation, where appropriate. This notation is generally more verbose than common nomenclature, but has the advantage of being more technically clear and descriptive.
Δx nomenclature cis,cis912 octadecadienoic acid In Δx (or delta-x) nomenclature, each double bond is indicated by Δx, where the double bond is located on the xth carbon–carbon bond, counting from the carboxylic acid end. Each double bond is preceded by a cis- or trans- prefix, indicating the conformation of the molecule around the bond. For example, linoleic acid is designated "cis-Δ9, cis-Δ12 octadecadienoic acid". This nomenclature has the advantage of being less verbose than systematic nomenclature, but is no more technically clear or descriptive.
nx nomenclature n−3 nx (n minus x; also ω−x or omega-x) nomenclature both provides names for individual compounds and classifies them by their likely biosynthetic properties in animals. A double bond is located on the xth carbon–carbon bond, counting from the terminal methyl carbon (designated as n or ω) toward the carbonyl carbon. For example, α-Linolenic acid is classified as a n−3 or omega-3 fatty acid, and so it is likely to share a biosynthetic pathway with other compounds of this type. The ω−x, omega-x, or "omega" notation is common in popular nutritional literature, but IUPAC has deprecated it in favor of nx notation in technical documents.[7] The most commonly researched fatty acid biosynthetic pathways are n−3 and n−6, which are hypothesized[by whom?] to decrease or increase, respectively,[citation needed] inflammation.
Lipid numbers 18:3
18:3ω6
18:3, cis,cis,cis-Δ91215
Lipid numbers take the form C:D, where C is the number of carbon atoms in the fatty acid and D is the number of double bonds in the fatty acid (if more than one, the double bonds are assumed to be interrupted by CH2 units, i.e., at intervals of 3 carbon atoms along the chain). This notation can be ambiguous, as some different fatty acids can have the same numbers. Consequently, when ambiguity exists this notation is usually paired with either a Δx or nx term.[7]

ProductionEdit

Fatty acids are usually produced industrially by the hydrolysis of triglycerides, with the removal of glycerol (see oleochemicals). Phospholipids represent another source. Some fatty acids are produced synthetically by hydrocarboxylation of alkenes.

Free fatty acidsEdit

Main article: fatty acid synthesis

The biosynthesis of fatty acids involves the condensation of acetyl-CoA. Since this coenzyme carries a two-carbon-atom group, almost all natural fatty acids have even numbers of carbon atoms.

The "uncombined fatty acids" or "free fatty acids" found in organisms come from the breakdown of a triglyceride[citation needed]. Because they are insoluble in water, these fatty acids are transported (solubilized, circulated) while bound to plasma protein albumin. The levels of "free fatty acid" in the blood are limited by the availability of albumin binding sites.

Fatty acids in dietary fats Edit

The following table gives the fatty acid, vitamin E and cholesterol composition of some common dietary fats.[9] [10]

Saturated Monounsaturated Polyunsaturated Cholesterol Vitamin E
g/100g g/100g g/100g mg/100g mg/100g
Animal fats
Lard 40.8 43.8 9.6 93 0.00
Duck fat[11] 33.2 49.3 12.9 100 2.70
Butter 54.0 19.8 2.6 230 2.00
Vegetable fats
Coconut oil 85.2 6.6 1.7 0 .66
Palm kernel oil 81.5 11.4 1.6 0 3.80
Palm oil 45.3 41.6 8.3 0 33.12
Cottonseed oil 25.5 21.3 48.1 0 42.77
Wheat germ oil 18.8 15.9 60.7 0 136.65
Soya oil 14.5 23.2 56.5 0 16.29
Olive oil 14.0 69.7 11.2 0 5.10
Corn oil 12.7 24.7 57.8 0 17.24
Sunflower oil 11.9 20.2 63.0 0 49.00
Safflower oil 10.2 12.6 72.1 0 40.68
Hemp oil 10 15 75 0
Canola/Rapeseed oil 5.3 64.3 24.8 0 22.21

Reactions of fatty acidsEdit

Fatty acids exhibit reactions like other carboxylic acids, i.e. they undergo esterification and acid-base reactions.

AcidityEdit

Fatty acids do not show a great variation in their acidities, as indicated by their respective pKa. Nonanoic acid, for example, has a pKa of 4.96, being only slightly weaker than acetic acid (4.76). As the chain length increases, the solubility of the fatty acids in water decreases very rapidly, so that the longer-chain fatty acids have minimal effect on the pH of an aqueous solution. Even those fatty acids that are insoluble in water will dissolve in warm ethanol, and can be titrated with sodium hydroxide solution using phenolphthalein as an indicator to a pale-pink endpoint. This analysis is used to determine the free fatty acid content of fats; i.e., the proportion of the triglycerides that have been hydrolyzed.

Hydrogenation and hardeningEdit

Hydrogenation of unsaturated fatty acids is widely practiced to give saturated fatty acids, which are less prone toward rancidification. Since the saturated fatty acids are higher melting than the unsaturated relatives, the process is called hardening. This technology is used to convert vegetable oils into margarine. During partial hydrogenation, unsaturated fatty acids can be isomerized from cis to trans configuration.[12]

More forcing hydrogenation, i.e. using higher pressures of H2 and higher temperatures, converts fatty acids into fatty alcohols. Fatty alcohols are, however, more easily produced from fatty acid esters.

In the Varrentrapp reaction certain unsaturated fatty acids are cleaved in molten alkali, a reaction at one time of relevance to structure elucidation.

Auto-oxidation and rancidityEdit

Main article: Rancidification

Unsaturated fatty acids undergo a chemical change known as auto-oxidation. The process requires oxygen (air) and is accelerated by the presence of trace metals. Vegetable oils resist this process because they contain antioxidants, such as tocopherol. Fats and oils often are treated with chelating agents such as citric acid to remove the metal catalysts.

OzonolysisEdit

Unsaturated fatty acids are susceptible to degradation by ozone. This reaction is practiced in the production of azelaic acid ((CH2)7(CO2H)2) from oleic acid.[12]

AnalysisEdit

In chemical analysis, fatty acids are separated by gas chromatography of methyl esters; additionally, a separation of unsaturated isomers is possible by argentation thin-layer chromatography.[13]

CirculationEdit

Digestion and intakeEdit

Main article: Digestion#Fat digestion

Short- and medium-chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein just as other absorbed nutrients do. However, long-chain fatty acids are not directly released into the intestinal capillaries. Instead they are absorbed into the fatty walls of the intestine villi and reassembled again into triglycerides. The triglycerides are coated with cholesterol and protein (protein coat) into a compound called a chylomicron.

Within the villi, the chylomicron enters a lymphatic capillary called a lacteal, which merges into larger lymphatic vessels. It is transported via the lymphatic system and the thoracic duct up to a location near the heart (where the arteries and veins are larger). The thoracic duct empties the chylomicrons into the bloodstream via the left subclavian vein. At this point the chylomicrons can transport the triglycerides to tissues where they are stored or metabolized for energy.

MetabolismEdit

Main article: Fatty acid metabolism

Fatty acids (provided either by ingestion or by drawing on triglycerides stored in fatty tissues) are distributed to cells to serve as a fuel for muscular contraction and general metabolism. They are consumed by mitochondria to produce ATP through beta oxidation.

DistributionEdit

Main article: Blood fatty acids

Blood fatty acids are in different forms in different stages in the blood circulation. They are taken in through the intestine in chylomicrons, but also exist in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) after processing in the liver. In addition, when released from adipocytes, fatty acids exist in the blood as free fatty acids.

It is proposed that the blend of fatty acids exuded by mammalian skin, together with lactic acid and pyruvic acid, is distinctive and enables animals with a keen sense of smell to differentiate individuals.[14]

See alsoEdit

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ReferencesEdit

  1. (1997) IUPAC Compendium of Chemical Terminology, 2nd, International Union of Pure and Applied Chemistry. URL accessed 2007-10-31.
  2. Ebert, D, Haller, RG; Walton, ME (2003 Jul 2). Energy contribution of octanoate to intact rat brain metabolism measured by 13C nuclear magnetic resonance spectroscopy.. The Journal of neuroscience : the official journal of the Society for Neuroscience 23 (13): 5928–35.
  3. Marin-Valencia, Isaac, Good, Levi B; Ma, Qian; Malloy, Craig R; Pascual, Juan M (17 October 2012). Heptanoate as a neural fuel: energetic and neurotransmitter precursors in normal and glucose transporter I-deficient (G1D) brain. Journal of Cerebral Blood Flow & Metabolism 33 (2): 175–182.
  4. Medscape: Free CME, Medical News, Full-text Journal Articles & More
  5. Christopher Beermann1, J Jelinek1, T Reinecker2, A Hauenschild2, G Boehm1, and H-U Klör2, "Short term effects of dietary medium-chain fatty acids and n-3 long-chain polyunsaturated fatty acids on the fat metabolism of healthy volunteers"
  6. Cell Biology: A Short Course
  7. 7.0 7.1 7.2 Rigaudy, J.; Klesney, S.P. (1979). Nomenclature of Organic Chemistry, Pergamon.
  8. (1977). The Nomenclature of Lipids. Recommendations, 1976. European Journal of Biochemistry 79 (1): 11–21.
  9. Food Standards Agency (1991). "Fats and Oils" McCance & Widdowson's the Composition of Foods, Royal Society of Chemistry.
  10. Ted Altar. More Than You Wanted To Know About Fats/Oils. Sundance Natural Foods Online. URL accessed on 2006-08-31.
  11. U. S. Department of Agriculture.. USDA National Nutrient Database for Standard Reference. U. S. Department of Agriculture.. URL accessed on 2010-02-17.
  12. 12.0 12.1 David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim.
    1. REDIRECT Template:Doi
  13. B. Breuer, T. Stuhlfauth et H. P. Fock, Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography, J. of Chromatogr. Science 25 (1987), S. 302-306 [1]
  14. includeonly>"Electronic Nose Created To Detect Skin Vapors", Science Daily, July 21, 2009. Retrieved on 2010-05-18.

External linksEdit

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