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[[fr:Acide gras]]

In [[chemistry]], especially [[biochemistry]], a '''fatty acid''' is an [[organic acid]] (or [[carboxylic acid]]), often with a long [[aliphatic]] tail (long chains), either [[saturated]] or [[unsaturated]]. Most of the natural fatty acid  have a even number of carbon atoms, because they are made up of [[acetate]] which has two carbon atoms. 

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.


==Saturated==

'''[[Saturated]]''' fatty acids are of the form

   O
 R-COH  , that is, R-[[Carboxyl|COOH]]

where 

 R = CH<sub>3</sub>-(CH<sub>2</sub>)<sub>n</sub>

Saturated are:
*[[Butyric acid|Butyric]]: CH<sub>3</sub>(CH<sub>2</sub>)<sub>2</sub>COOH 
*[[Palmitic acid|Palmitic]] (hexadecanoic acid): CH<sub>3</sub>(CH<sub>2</sub>)<sub>14</sub>COOH 
*[[Stearic acid|Stearic]]: CH<sub>3</sub>(CH<sub>2</sub>)<sub>16</sub>COOH 
 
==Unsaturated==

Unsaturated fatty acids are of similar form, except that one or more [[alkene]] [[functional group]]s exist along the chain, substituting singly-[[chemical bond|bond]]ed

 -CH<sub>2</sub>-CH<sub>2</sub>-

part of the chain with '''[[double bond|doubly-bonded]]'''

  -CH=CH-  

portions (this is, with carbons attached with a double bond to another carbon). In most of these, each double bond has 3''n'' carbon atoms after it, for some n, and are all [[cis]] bonds.

There are two different ways to make clear were this [[double bond]]s are located in the molecule. For example:

Delta-9,12 or &#916;<sup>9,12</sup> : The [[double bond]] are the nineth and twelfth carbon-carbon bond counting from the end of the chain with the [[carboxyl group]].

Omega-3 or &#937;<sup>-3</sup> : The first [[double bond]] is the third carbon-carbon bond counting from the end of the chain most distant from the [[carboxyl group]]. The  next 

*Linolenic 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 , is an [[omega-3 fatty acid]].
*Arachidonic and linoleic  are  [[omega-6 fatty acid]]s.
*Oleic CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>'''CH=CH'''(CH<sub>2</sub>)<sub>7</sub>COOH and erucic and oleic 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 H, while oleic acid is an unsaturated fatty acid (with two less H than the anterior). 

[[image:rasyslami.jpg]] <br>

<center>'''Image'''.Several fatty acid molecules </center>

'''[[Essential fatty acid]]s or polyunsaturated fatty acids''' are fatty acids that are required in the human diet. This means they cannot be synthesized by the body and must be obtained from food. We can easily make saturated fatty acids and unsaturated fatty acids that have one double bond (monounsaturated fatty acids), but we do not have the proper enzymes to synthesis unsaturated fatty acids that have more than one double bond (polyunsaturated fatty acids).

These essential fatty acids are very important to our immune system and to help us regulate our blood pressure, for they are used to make essential compounds, such as [[prostaglandin]]s.

== Free Fatty Acids==

Fatty acids not bound or attached to other molecules, like [[triglyceride]]s or [[phospholipid]]s.

The '''uncombined fatty acids''' or Free Fatty Acids may come from the breakdown of a triglyceride into its components (fatty acids and glycerol). 

Free fatty acids are an important source of fuel for many tissues since they can yield relatively large quantities of [[ATP]].  Typically 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, brain cannot use fatty acids as a source of fuel, relying instead on glucose.

==pH==

Long chain fatty acids do not have a [[pH]]. pH is a measure of acidity (or alkalinity) of an aqueous solution. Since long chain fatty acids are insoluble in water, it is difficult to measure their pH.



See also : [[triglyceride]]s.

[[de:Fetts�ure]] [[es:�cido graso]] [[ja:&#33026;&#32938;&#37240;]]

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====References====
* Adapted from the [[Wikipedia]] article, "Fatty_acid" [http://en.wikipedia.org/wiki/Fatty_acid http://en.wikipedia.org/wiki/Fatty_acid], used under the [[GNU Free Documentation License]]