Fatty acid: Difference between revisions

{{Fats}}

[[Image:rasyslami.jpg|thumb|right|300px|Three-dimensional representations of several fatty acids. [[Saturated and unsaturated compounds|Saturated]] fatty acids have perfectly straight chain structure. [[Unsaturated compound|Unsaturated]] ones are typically bent, unless they have a [[#Unsaturated fatty acids|trans]] configuration.]]

 

==History==

 

==Types of fatty acids==

Fatty acids are classified in many ways: by length, by saturation vs unsaturation, by even vs odd carbon content, and by linear vs branched.

 

|+ Examples of saturated fatty acids

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| [[Caprylic acid]] || CH{{sub|3}}(CH{{sub|2}}){{sub|6}}COOH || 8:0

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.

 

; ''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.

 

 

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).

|+ Examples of Unsaturated Fatty Acids

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===Even- vs odd-chained fatty acids===

 

===Branching===

===Carbon atom numbering===

{{See also|Essential fatty acid#Nomenclature and terminology}}

 

Most naturally occurring fatty acids have an [[branched chain fatty acids|unbranched chain]] of carbon atoms, with a [[carboxyl group]] (–COOH) at one end, and a [[methyl group]] (–CH3) at the other end.

Another convention uses letters of the [[Greek alphabet]] in sequence, starting with the first carbon ''after'' the carboxyl group. Thus carbon α ([[alpha]]) is C-2, carbon β ([[beta]]) is C-3, and so forth.

 

 

 

The notation Δ^{''x'',''y'',...} is traditionally used to specify a fatty acid with double bonds at positions ''x'',''y'',.... (The capital Greek letter "Δ" ([[Delta (letter)|delta]]) corresponds to [[Latin alphabet|Roman]] "D", for '''D'''ouble bond). Thus, for example, the 20-carbon [[arachidonic acid]] is Δ^5,8,11,14, meaning that it has double bonds between carbons 5 and 6, 8 and 9, 11 and 12, and 14 and 15.

 

 

Fatty acids with an [[odd number]] of carbon atoms are called [[odd-chain fatty acid]]s, whereas the rest are even-chain fatty acids. The difference is [[gluconeogenesis#Precursors|relevant to gluconeogenesis]].

!''n''−''x'' <br />(or ω−''x'')

|[[Omega-3 fatty acid|''n''−3]]<br />(or [[Omega-3 fatty acid|ω−3]])

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!Lipid numbers

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===Industrial===

 

===By animals===

{{main|Fatty acid synthesis}}

 

 

 

The "uncombined fatty acids" or "free fatty acids" found in the circulation of animals come from the breakdown (or [[lipolysis]]) of stored triglycerides.<ref name=stryer /><ref>{{cite journal | last1 = Zechner | first1 = R. | last2 = Strauss | first2 = J. G. | last3 = Haemmerle | first3 = G. | last4 = Lass | first4 = A. | last5 = Zimmermann | first5 = R. | year = 2005 | title = Lipolysis: pathway under construction | journal = Curr. Opin. Lipidol. | volume = 16 | issue = 3| pages = 333–340 | doi = 10.1097/01.mol.0000169354.20395.1c | pmid = 15891395 | s2cid = 35349649 }}</ref> Because they are insoluble in water, these fatty acids are transported bound to plasma [[albumin]]. The levels of "free fatty acids" in the blood are limited by the availability of albumin binding sites. They can be taken up from the blood by all cells that have mitochondria (with the exception of the cells of the [[central nervous system]]). Fatty acids can only be broken down in mitochondria, by means of [[beta-oxidation]] followed by further combustion in the [[citric acid cycle]] to CO{{sub|2}} and water. Cells in the central nervous system, although they possess mitochondria, cannot take free fatty acids up from the blood, as the [[blood–brain barrier]] is impervious to most free fatty acids,{{citation needed|date=June 2016}} excluding [[short-chain fatty acid]]s and [[medium-chain fatty acid]]s.<ref name="SCFA MCT-mediated BBB passage - 2005 review">{{cite journal | vauthors = Tsuji A | title = Small molecular drug transfer across the blood–brain barrier via carrier-mediated transport systems | journal = NeuroRx | volume = 2 | issue = 1 | pages = 54–62 | year = 2005 | pmid = 15717057 | pmc = 539320 | doi = 10.1602/neurorx.2.1.54 | quote = Uptake of valproic acid was reduced in the presence of medium-chain fatty acids such as hexanoate, octanoate, and decanoate, but not propionate or butyrate, indicating that valproic acid is taken up into the brain via a transport system for medium-chain fatty acids, not short-chain fatty acids.&nbsp;... Based on these reports, valproic acid is thought to be transported bidirectionally between blood and brain across the BBB via two distinct mechanisms, monocarboxylic acid-sensitive and medium-chain fatty acid-sensitive transporters, for efflux and uptake, respectively.}}</ref><ref name="SCFA MCT-mediated BBB passage - 2014 review">{{cite journal | vauthors = Vijay N, Morris ME | title = Role of monocarboxylate transporters in drug delivery to the brain | journal = Curr. Pharm. Des. | volume = 20 | issue = 10 | pages = 1487–98 | year = 2014 | pmid = 23789956 | pmc = 4084603 | doi = 10.2174/13816128113199990462| quote = Monocarboxylate transporters (MCTs) are known to mediate the transport of short chain monocarboxylates such as lactate, pyruvate and butyrate.&nbsp;... MCT1 and MCT4 have also been associated with the transport of short chain fatty acids such as acetate and formate which are then metabolized in the astrocytes [78].}}</ref> These cells have to manufacture their own fatty acids from carbohydrates, as described above, in order to produce and maintain the phospholipids of their cell membranes, and those of their organelles.<ref name=stryer />

 

====Variation between animal species====

 

==Fatty acids in dietary fats==

Solutions of fatty acids in [[ethanol]] can be [[titration|titrated]] with [[sodium hydroxide]] solution using [[phenolphthalein]] as an indicator. 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.

 

 

===Hydrogenation and hardening===

 

More forcing hydrogenation, i.e. using higher pressures of H{{sub|2}} and higher temperatures, converts fatty acids into [[fatty alcohol]]s. Fatty alcohols are, however, more easily produced from fatty acid [[ester]]s.

 

===Ozonolysis===

 

==Circulation==

====Essential fatty acids====

{{Main|Essential fatty acid}}

 

===Distribution===

The chemical analysis of fatty acids in lipids typically begins with an [[interesterification]] step that breaks down their original esters (triglycerides, waxes, phospholipids etc.) and converts them to [[methyl]] esters, which are then separated by gas chromatography<ref>{{cite journal | vauthors = Aizpurua-Olaizola O, Ormazabal M, Vallejo A, Olivares M, Navarro P, Etxebarria N, Usobiaga A | display-authors = 6 | title = Optimization of supercritical fluid consecutive extractions of fatty acids and polyphenols from Vitis vinifera grape wastes | journal = Journal of Food Science | volume = 80 | issue = 1 | pages = E101-7 | date = January 2015 | pmid = 25471637 | doi = 10.1111/1750-3841.12715 }}</ref> or analyzed by [[gas chromatography]] and mid-[[infrared spectroscopy]].

 

 

==Industrial uses==

 

Esters of fatty acids with simpler alcohols (such as methyl-, ethyl-, n-propyl-, isopropyl- and butyl esters) are used as emollients in cosmetics and other personal care products and as synthetic lubricants. Esters of fatty acids with more complex alcohols, such as [[sorbitol]], [[ethylene glycol]], [[diethylene glycol]], and [[polyethylene glycol]] are consumed in food, or used for personal care and water treatment, or used as synthetic lubricants or fluids for metal working.

[[File:Myristic-acid-3D-vdW.png|thumb|left|500px|A [[space-filling model]] of the saturated fatty acid [[myristic acid]]]] The two-dimensional illustration has implicit hydrogen atoms bonded to each of the carbon atoms in the polycarbon tail of the [[myristic acid]] molecule (there are 13 carbon atoms in the tail; 14 carbon atoms in the entire molecule).

 

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* [[List of carboxylic acids]]

* [[Vegetable oil]]

{{colend}}

 

==References==

<ref name=rayn1991>{{cite journal | vauthors = Raynard RS, Cossins AR | title = Homeoviscous adaptation and thermal compensation of sodium pump of trout erythrocytes | journal = The American Journal of Physiology | volume = 260 | issue = 5 Pt 2 | pages = R916–24 | date = May 1991 | pmid = 2035703 | doi = 10.1152/ajpregu.1991.260.5.R916 | s2cid = 24441498 }}</ref>

 

 

<ref name=hulb2003xa>{{cite journal | vauthors = Hulbert AJ | title = Life, death and membrane bilayers | journal = The Journal of Experimental Biology | volume = 206 | issue = Pt 14 | pages = 2303–11 | date = July 2003 | pmid = 12796449 | doi = 10.1242/jeb.00399 | doi-access = free }}</ref>

 

==External links==