Fatty acid

From The School of Biomedical Sciences Wiki
Jump to: navigation, search

Fatty acids are carboxylic acids with carbon chain length ranging from 10 to 30 atoms.

Fatty acids are an essential part of the human body, they make up part of all cell membranes and are a vital energy source. A fatty acid is made up o two functional chemical regions, one being the hydrophilic carboxylic acid head that covalently links to other fatty acids. The second is a long chain of hydrocarbons which are hydrophobic and chemically unreactive. The chain is either saturated and contains no double carbon-carbon bonds and the maximum number of hydrogen atoms (palmitic acid) or unaturated and contain double bonds (oleic acid.) Fatty acids in the form of triacylglycerol are stored in the cytoplasm of some cells, this consists of three fatty acid chains linked to a molecule of glycerol. When used for energy in the body the fatty acid chains are released and form two carbon units and enter the same metabolism as glucose. Fatty acids are a common type of lipid, insoluble in water but soluble in fat. The fatty acid chains form phospholipids in cell membranes, with two fatty acids attached to glycerol and the third attached to a phosphate group. Phospholipids consist of a hydrohobic tail (fatty acid chains) and a hydrophilic head (phosphate) making them amphiphilic. This structural propertis enable the lipids to form a lipid bilayer, the basis of a cell membrane .

Basic Chemistry

In fatty acids hydrophobic long carbon chain dominates in chemical properties the hydrophilic carboxyl group and gives the whole molecule hydrophobic character [1].

Naturally occurring fatty acids usually contain an even number of carbon atoms. The most common are 16 and 18 atoms long. The carbon skeleton is unbranched with a few exceptions. Longer carbon chain promotes stronger intermolecular interactions. This means that fatty acids with longer carbon chain have higher melting points (see Table 1). Some fatty acids contain double bonds in their alkyl chain. These are predominately in cis configuration, which results in "kinks" in the chain shape, in contrast with straight saturated acids. Effectively, straight acid fatty acids can "pack" closer together and therefore have higher melting points due to stronger molecular interactions (see Table 1) [2].  

Table 1 [3][4]

Trivial Name  Trivial carboxylate name Formal Name Designation Melting Point (°C)
Lauric Acid lauroyl dodecanoyl 12:0 +44
Myristic Acid myristoyl tetradecanoyl 14:0 +54
Palmitic Acid palmitoyl hexadecanoyl 16:0 +63
Stearic Acid stearoyl octadecanoyl 18:0 +70
Oleic Acid oleoyl cis-9-octadecenoyl 18:1c Δ9 +13
Linoleic Acid linoleoyl di-cis-9,12-octadecadienoyl 18:2cc Δ9,12 -5
Linolenic Acid linolenoyl all-cis-9, 12,15-octadecatrienoyl 18:3ccc Δ9,12,15 -11
Arachidonic Acid arachidonoyl all-cis-5,8,11,14-eicosatetraenoyl 20:4cccc Δ5,8,11,14 -50

Nomenclature

Systematic names for fatty acids are derived from their parent hydrocarbon names by adding the suffix -oic. Thereby, the fatty acid with 16 carbon atoms is called hexadecanoic acid. A monounsaturated fatty acid with 16 carbon atoms is called hexadecenoic acid. Fatty acids with 2 and 3 double bonds are called hexadecadienoic and hexadecatrienoic respectively. Trivial names are also commonly used (see Table 1). Greek letter Δ followed by a superscript number denotes the position of a double bond. Also, because at physiological pH fatty acids form ions, it is appropriate to reffer to them accordingly (see Table 1) [5].

References    

  1. Charles E. Ophardt, 2003. Virtual Chembook. [online] Available at http://www.elmhurst.edu/~chm/vchembook/551fattyacids.html [Accessed 11 January 2011]
  2. Jeremy M. Berg, John L. Tymoczko, Lubert Stryer, 2002. Biochemistry. 5th ed. New York: W. H. Freeman and Company
  3. Charles E. Ophardt, 2003. Virtual Chembook. [online] Available at http://www.elmhurst.edu/~chm/vchembook/551fattyacids.html [Accessed 11 January 2011]
  4. Jeremy M. Berg, John L. Tymoczko, Lubert Stryer, 2002. Biochemistry. 5th ed. New York: W. H. Freeman and Company
  5. Jeremy M. Berg, John L. Tymoczko, Lubert Stryer, 2002. Biochemistry. 5th ed. New York: W. H. Freeman and Company
Personal tools
Namespaces
Variants
Actions
Navigation
Toolbox