Témbongkeun sumber pikeun Asam lemak

{{Lemak}}
Dina [[kimia]], utamana [[biokimia]], '''asam lemak''' nyaéta [[asam karboksilat]] anu ilaharna diwangun ku buntut/ranté [[alifatik]], boh nu [[kejenuhan (kimia)|jenuh]] atawa [[sanyawa teu jenuh|henteu]]. Asam lemak dijieun tina [[hidrolisis]] beungkeut [[éster]] dina lemak atawa minyak biologis (nyaéta [[trigliserida]]), ku cara ngaleupaskeun [[gliserol]] (baca [[oléokimia]]).

Asam lemak téh asam monokarboksilat alifatik nu diturunkeun tina atawa dikandung dina bentuk éster lemak, minyak, atawa lilin sato (gajih) jeung tutuwuhan. Asam lemak alami biasana ngandung ranté 4-28 karbon (teu nyagak sarta jumlahna genap), boh jenuh atawa henteu. Istilah ieu ogé kadang ngawengku sakabéh asam karboksilat alifatik asiklik<ref name=iupac>
{{cite book| url=http://goldbook.iupac.org/F02330.html |title= The Gold Book |series =IUPAC Compendium of Chemical Terminology|edition= 2nd |year=1997|
publisher = International Union of Pure and Applied Chemistry|
accessdate=2007-10-31| isbn=052151150X| author=Prayer Book,}}</ref>. Ku kituna, [[asam asetat]] gé jadi kaasup asam lemak, padahal bisa leyur dina cai alatan pondok pisan ranté karbonna.
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==Types== 
[[Image:rasyslami.jpg|thumb|right|300px|Three dimensional representations of several fatty acids]]
Fatty acids can be saturated and unsaturated, depending on [[double bond]]s. They differ in length as well.

===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 atoms.

Saturated fatty acids form straight chains and, as a result, can be packed together very tightly, allowing living organissms 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 [[Naming convention|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 in either a [[Geometric isomerism|cis-]] or [[Geometric isomerism|trans-]] conformation, and stands 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, but rather, mono- or polyunsaturated.

Most commonly-occurring saturated fatty acids are of the following varieties:

{| class="wikitable"
|'''Common name''' || '''IUPAC name''' || '''Chemical structure''' || '''Abbr.''' || '''Melting point''' (°C)
|-
|[[Butyric acid|Butyric]] || Butanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>2</sub>COOH ||  C4:0||  -8
|-
|[[Caproic acid|Caproic]] || Hexanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>COOH ||  C6:0||  -3
|-
|[[Caprylic acid|Caprylic]] || Octanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>COOH ||  C8:0||  16-17
|-
|[[Capric acid|Capric]] || Decanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>8</sub>COOH ||  C10:0||  31
|-
|[[Lauric acid|Lauric]] || Dodecanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>10</sub>COOH ||  C12:0||  44-46
|-
|[[Myristic acid|Myristic]] || Tetradecanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>12</sub>COOH ||  C14:0||  58.8
|-
|[[Palmitic acid|Palmitic]] || Hexadecanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>14</sub>COOH ||  C16:0||  63-64
|-
|[[Stearic acid|Stearic]] || Octadecanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>16</sub>COOH ||  C18:0||  69.9
|-
|[[Arachidic acid|Arachidic]] || Eicosanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>18</sub>COOH ||  C20:0||  75.5
|-
|[[Behenic acid|Behenic]] || Docosanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>20</sub>COOH ||  C22:0||  74-78
|-
|[[Lignoceric acid|Lignoceric]] || Tetracosanoic acid || CH<sub>3</sub>(CH<sub>2</sub>)<sub>22</sub>COOH ||  C24:0||  
|}

===Unsaturated fatty acids===
[[Image:Isomers of oleic acid.png|thumb|300px|right|Comparison of the ''trans'' isomer (top) and the ''cis''-isomer of [[oleic acid]].]]
Unsaturated fatty acids are of similar form, except that one or more [[alkenyl]] functional groups exist along the chain, with each alkene substituting a single-[[chemical bond|bond]]ed " -CH<sub>2</sub>-CH<sub>2</sub>-" part of the chain with a [[Covalent bond|double-bonded]] "-CH=CH-" portion (that is, a carbon double-bonded to another carbon).

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.

; ''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 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 (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).

====Nomenclature====
There are several different systems of nomenclature in use for [[unsaturated compound|unsaturated]] fatty acids. The following table describes the most common systems.

{| 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 do not follow any pattern, but are concise and generally unambiguous.
|-
!Systematic nomenclature
|[[Oleic acid|(9Z)-octadec-9-enoic 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]] |date=1979 |isbn=0080223699 |oclc=5008199}}</ref> along with a recommendation published specifically for lipids in 1977.<ref name="nomenclature-1977">{{cite journal |date=1977 |title=The Nomenclature of Lipids. Recommendations, 1976 |work=European Journal of Biochemistry |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>]]
|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 .
|-
!''n''−''x'' nomenclature
|[[Omega-3 fatty acid|''n''−3]]
|'''''n''−''x''''' ('''''n'' minus ''x'''''; also '''ω−''x''''' or '''omega-''x''''') '''nomenclature''' does not provide names for individual compounds, but is a shorthand way to categorize fatty acids by their physiological properties. A double bond is located on the ''x''th 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 shares properties with other compounds of this type. The ω−''x'' or omega-''x'' notation is common in popular 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 types are [[omega-3 fatty acid|''n''−3]] and [[omega-6 fatty acid|''n''−6]], which have unique biological properties.
|-
!Lipid numbers
|18:3<br />[[Gamma-linolenic acid|18:3,&nbsp;''n''−6]]<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. This notation is ambiguous, as different fatty acids can have the same numbers. Consequently, this notation is usually paired with either a Δ<sup>''x''</sup> or ''n''−''x'' term.<ref name="nomenclature-1979" />
|}

Examples of unsaturated fatty acids: 
{| class="wikitable"
|-
! Common name || Chemical structure || Δ<sup>''x''</sup> || ''C'':''D'' || ''n''−''x''
|-
|[[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
|-
|[[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
|-
|[[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]]
|-
|[[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]]
|-
|[[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]]
|-
|[[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]]
|-
|[[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====
{{main|Essential fatty acid}}

The human body can produce all but two of the fatty acids it needs. These two, [[linoleic acid]] (LA acid) and [[alpha-linolenic acid]] (ALA), are widely distributed in plant oils. In addition, fish oils contain the longer-chain omega-3 fatty acids [[eicosapentaenoic acid]] (EPA) and [[docosahexaenoic acid]] (DHA). Other marine oils, such as from seal, also contain significant amounts of [[docosapentaenoic acid]] (DPA), which is also an omega-3 fatty acid. Although the body to some extent can convert LA and LNA into these longer-chain omega-3 fatty acids, the omega-3 fatty acids found in marine oils help fulfill the requirement of essential fatty acids (and have been shown to have wholesome properties of their own).

Since they cannot be made in the body from other substrates and must be supplied in food, they are called essential fatty acids.  Mammals lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10.  Hence linoleic acid and alpha-linolenic acid are essential fatty acids for humans.

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.

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 position or omega-6 position.

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 <ref>{{cite news |title= Study Links Brain Fatty Acid Levels To Depression |url= http://www.sciencedaily.com/releases/2005/05/050525161319.htm |work= ScienceDaily |publisher= American Society For Biochemistry And Molecular Biology |location=Bethesda, MD  |date= 2005-05-25|accessdate=2008-01-18 }}</ref> 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 diet richer in omega-3 fatty acids, or consumption of supplements to compensate for a dietary imbalance, has been associated with reduced violent behavior<ref name="prison">{{cite journal
 | 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 behavior 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
 | doi = 10.1192/bjp.181.1.22
 | pmid = 12091259
 }} </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{{Fact|date=February 2007}}<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
 | pmid = 15867048
 }} </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 | isbn = 0-14-101566-7 | oclc = 224019274 55482837 55588726 57432047 }}</ref><ref>{{cite web | title = Using Fatty Acids for Enhancing Classroom Achievement | url = http://www.durhamtrial.org/ | accessmonthday = January | accessyear = 2004 }}</ref>

Fatty acids play an important role in the life and death of cardiac cells because they are essential fuels for mechanical and electrical activities of the heart. <ref>{{cite journal 
 | title=External blockade of the major cardiac delayed-rectifier K+ channel (Kv1.5) by polyunsaturated fatty acids 
 | url=http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=43279&pageindex=1#page | format= 
 |author= E Honoré, J Barhanin, B Attali, F Lesage, and M Lazdunski
 | journal= Proc Natl Acad Sci USA|year= 1994 March 1|volume= 91(5)|pages=1937–1941
 | accessdate=2007-01-18 
 | pmid=8127910}} - see page 1 of this link</ref> 
<ref name="pmid16919517">{{cite journal |author=Reiffel JA, McDonald A |title=Antiarrhythmic effects of omega-3 fatty acids |journal=Am. J. Cardiol. |volume=98 |issue=4A |pages=50i–60i |year=2006 |pmid=16919517 |doi=10.1016/j.amjcard.2005.12.027}}</ref>
<ref name="pmid17086218">{{cite journal |author=Landmark K, Alm CS |title=Alpha-linolenic acid, cardiovascular disease and sudden death |language=Norwegian |journal=Tidsskr. Nor. Laegeforen. |volume=126 |issue=21 |pages=2792–4 |year=2006 |pmid=17086218 |doi= }}</ref>
<ref name="pmid17091903">{{cite journal |author=Herbaut C |title=Omega-3 and health |language=French |journal=Rev Med Brux |volume=27 |issue=4 |pages=S355–60 |year=2006 |pmid=17091903 |doi= }}</ref>

====Trans fatty acids====
{{main|Trans fat}}

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 amounts of trans fats correlate with circulatory diseases such as [[atherosclerosis]] and [[coronary heart disease]] more than the same amount of non-trans fats, for reasons that are not fully understood. It is known, however, that trans fats raise the LDL (bad) cholesterol and lowers the HDL (good) cholestrol. They have also been shown to have other harmful effects such as increasing triglycerides and Lp(a) lipoproteins. It is also thought to cause more inflammation, which is thought to occur through damage to the cells lining of blood vessels.

===Long and short===
In addition to saturation, fatty acids are short, medium or long.

*[[Short chain fatty acid]]s (SCFA) are [[fatty acids]] with [[aliphatic]] tails of less than eight [[carbons]].
*Medium chain fatty acids (MCFA) are [[fatty acids]] with [[aliphatic]] tails of 8–14 <ref name=lipidworld> [http://www.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] Christopher Beermann1, J Jelinek1, T Reinecker2, A Hauenschild2, G Boehm1  and H-U Klör2 </ref> [[carbons]], which can form [[medium chain triglycerides]].
*Long chain fatty acids (LCFA) are [[fatty acids]] with [[aliphatic]] tails of 16 [[carbons]] or more<ref name=lipidworld/>.

When discussing [[essential fatty acid]]s, (EFA) a slightly different terminology applies.  
Short-chain EFA are 18 carbons long; long-chain EFA have 20 or more carbons.<ref name="Fats of Life">{{cite web |url=http://www.fatsoflife.com/fatsoflife/fat-basics.asp |title=Health Facts About Good Fats : The Basics : Omega-3s, Mono & Polyunsaturated Fatty Acids |accessdate=2007-12-12 |format= |work=Fats of Life Newsletter}}</ref>

==Free fatty acids==
Fatty acids can be bound or attached to other molecules, such as in [[triglyceride]]s or [[phospholipid]]s.  When they are not attached to other molecules, they are known as "free" fatty acids.

The '''uncombined fatty acids''' or '''free fatty acids''' may come from the breakdown of a triglyceride into its components (fatty acids and glycerol). However as fats are insoluble in water they must be bound to appropriate regions in the plasma protein albumin for transport around the body. The levels of "free fatty acid" in the blood are limited by the number of albumin binding sites available.

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.  In particular, heart and skeletal muscle prefer fatty acids.  The brain cannot use fatty acids as a source of fuel; it relies on glucose, or on [[ketone bodies]]. Ketone bodies are produced in the liver by [[fatty acid metabolism]] during starvation, or during periods of low carbohydrate intake.

== 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
 | title=McCance & Widdowson's the Composition of Foods
 | chapter=Fats and Oils
 | author=Food Standards Agency
 | publisher=Royal Society of Chemistry
 | year=1991
}}</ref>
<ref>
{{cite web
 | url=http://www.efn.org/~sundance/fats_and_oils.html
 | title=More Than You Wanted To Know About Fats/Oils
 | author=Ted Altar
 | accessdate=2006-08-31
 | publisher=Sundance Natural Foods Online
}}
</ref>

{| class="wikitable" |
|+ 
! !! Saturated !! Monounsaturated !! Polyunsaturated !! Cholesterol !! Vitamin E
|-
| || align="center" | g/100g || align="center" | g/100g || align="center" | g/100g || align="center" | mg/100g || align="center" | mg/100g
|-
| colspan="6" | '''''Animal fats'''''
|-
| [[Lard]] || align="right" |  40.8 || align="right" |  43.8 || align="right" |  9.6 || align="right" |  93 || align="right" |  0.00
|-
| [[Butter]] || align="right" |  54.0 || align="right" |  19.8 || align="right" |  2.6 || align="right" |  230 || align="right" |  2.00
|-
| colspan="6" | '''''Vegetable fats'''''
|-
| [[Coconut oil]] || align="right" |  85.2 || align="right" |  6.6 || align="right" |  1.7 || align="right" |  0 || align="right" |  .66
|-
| [[Palm oil]] || align="right" |  45.3 || align="right" |  41.6 || align="right" |  8.3 || align="right" |  0 || align="right" |  33.12
|-
| [[Cottonseed oil]] || align="right" |  25.5 || align="right" |  21.3 || align="right" |  48.1 || align="right" |  0 || align="right" |  42.77
|-
| [[Wheat germ oil]] || align="right" |  18.8 || align="right" |  15.9 || align="right" |  60.7 || align="right" |  0 || align="right" |  136.65
|-
| [[Soya oil]] || align="right" |  14.5 || align="right" |  23.2 || align="right" |  56.5 || align="right" |  0 || align="right" |  16.29
|-
| [[Olive oil]] || align="right" |  14.0 || align="right" |  69.7 || align="right" |  11.2 || align="right" |  0 || align="right" |  5.10
|-
| [[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;
|-
| [[Safflower oil]] || align="right" |  10.2 || align="right" |  12.6 || align="right" |  72.1 || align="right" |  0 || align="right" |  40.68
|-
| [[Canola|Rapeseed/Canola oil]] || align="right" |  5.3 || align="right" |  64.3 || align="right" |  24.8 || align="right" |  0 || align="right" |  22.21
|}

==Acidity==
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 has relevance only to the types of reactions in which they can take part.

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.

==Reaction of fatty acids==

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 also 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. 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===
{{main|Rancidification}}

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]].

==Circulation==
===Digestion and intake===
{{Main|Digestion#Fat digestion}}
[[Short chain fatty acids|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 too large to be directly released into the tiny intestine 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 where they are needed.

===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]].
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== Rujukan ==
* ''[[:en:Fatty acid|Fatty acid]]''. Wikipédia basa Inggris. Disalin 7 Oktober 2008.
{{reflist}}

== Baca ogé ==
{{Commons|Fatty acids}}
* [[Asam lemak ésénsial]]
* [[Lemak jenuh]]
* [[Lemak teu jenuh]]
* [[Sintésis asam lemak]]
* [[Métabolismeu asam lemak]]
* [[Minyak nabati]]

== Tumbu kaluar ==
* [http://www.lipidlibrary.co.uk/ Lipid Library]
* [http://intl.elsevierhealth.com/journals/plef/ ''Prostaglandins, Leukotrienes & Essential Fatty Acids'' Journal] {{Webarchive|url=https://web.archive.org/web/20071012173913/http://intl.elsevierhealth.com/journals/plef/ |date=2007-10-12 }}

{{Asam lemak}}

{{pondok}}

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