Understanding Fatty acids Classification


Answer to Biochemistry Question about Lipids (L-03)


Answer: (f)






Another notation: CH3-(CH2 )14 – COOH


Another notation: C16:0 (It means, 16 carbons, no double bonds)


Palmitic acid or hexadecanoic acid is a 16 carbon fatty acid,  It is the most common fatty saturated acid found in plants and animals (no the most abundant, though). It was purified from Palm oil, and it was named after it. Humans can synthetize it, so it is non essential.





Fatty acids are carboxylic acids derived or contained in lipids. They show the general formula


R-COOH  (R-COO- for free fatty acids at physiological pH)


Where R is usually a lineal (unbranched) carbon chain with an even number of carbons.(Funny mistake found in different textbooks…when you think about it, R has an odd number of carbons, so the fatty acid (R + COOH) has an even number of Carbons)

Natural fatty acids usually contain 4 to 28 carbons (Most of the fatty acids in complex lipids contain 14 to 22 carbons, though).


The function of fatty acids are:


            Biological fuel


            Components of more complex lipids


There are multiple classifications of fatty acids. The most used, from the biomedical point of view are:


CHEMICAL: According to the presence of double bonds in the carbon chain:


         Saturated (no double bonds)


            CH3-CH2– CH2– CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH


         Unsaturated (one or more double bonds)


            CH3– CH2– CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH


According to the numbers of double bonds


        monounsaturated (just one double bond)


                        CH3– CH2– CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH


        polyunsaturated. (more than one double bond)


                        CH3– CH2– CH=CH-CH2-CH=CH-CH2-CH2-CH2-CH2-COOH



According to the position of the double bond relative to the last carbon of the chain (sometimes called Metabolic classification)


          Omega 3 (the double bond nearest the last carbon of the chain (Cw)  is 3 carbons apart from the end of the chain)


                         CH3– CH2– CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH


           Omega 6 (the doble bond nearest to the last carbon of the chain is 6 carbon apart)


                        CH3– CH2– CH2-CH2-CH2– CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-COOH                


According to the geometric configuration


          Cis fatty acids (both part of the chain adjacent to the double bond are at the same side of the double bond)


          Trans fatty acids (the two parts or the chain adjacent to the double bond are in opposite side or the double bond)



                                            Trans and cis fatty acids



BIOLOGICAL (also called Nutritional classification)


         Essential: Non synthesized by animals. Should be obtained from the diet. Linoleic and Linolenic.


         Non essential: Synthesized by animals.  All the others.




There are different classifications based on the number of carbons


Short chain fatty acids: 2 to 6 carbons

Medium Chain: 8 to 14 carbons

Long Chain fatty acids: 16 carbons and up.



Another classification based on the number of carbons:


Short chain  2-4 carbons

Medium chain 6-12 carbons

Long chain 14-22 carbons

Very long chain 24 -26 carbons


Some texts differ in relation to exactly how many carbons a fatty acid should have for belonging to one of these groups. For example, some texts consider a Fatty acid with more than 20 C as a VLCFA,



Only when we know these classifications we are able to understand plently expressions like:


“Saturated fatty acids and trans fatty acids increase cholesterol concentration in blood, while unsaturated fatty acids decrease it.”


“Oils are rich in unsaturated fatty acids”


“Medium Chain Acyl Co A Dehydrogenase Deficiency, the most common inborn error of faty acid oxidation, has been related to Sudden Infant Death Syndrome”


“Defects in the oxidation of Very Long Chain Fatty Acids, is the main metabolic defect found in  Zellweger Syndrome and X-linked adrenoleukodistrophy.”


“When following a Fat free diet, it is important to supplement with Liposolubles vitamins and essential fatty acids”


“Vegetable oils are rich in Omega6 fatty acids, while fish oils are rich in Omega3”




Some examples of biological interest:


Omega 3

Alphalinolenic acid (from the biological point of view, it is also essential) alphalinoleic acid, essential




Linoleic acid  

Linoleic acid 


Omega 9

                 Oleic acid (non essential)


Oleic acid




Three-dimensional representation of Fatty acids of different groups:


tridimensional representation of fatty acids



More information about Fatty acids:


Very good review in Wikipedia


The Medical Biochemistry page/lipids/fatty acids


Fatty acids in Cyberlipid.org

14 thoughts on “Understanding Fatty acids Classification

  1. Pingback: Questions about Lipid structure and functions « The Biochemistry Questions Site

  2. Pingback: Understanding the classification of Lipids « The Biochemistry Questions Site

  3. l love all those people which love biochem. it is my life , my shelter my aim and my family . love and peace for all.

  4. please do mention of PUFA , and its biological requirement to prevent Cardiac problems like ARTERIOSCLEROSIS and HYPER LIPIDEMIA etc., Thankyou

  5. please do mention of PUFA , and its biological requirement to prevent Cardiac problems like ARTERIOSCLEROSIS and HYPER LIPIDEMIA etc., Thankyou and it is very useful to teach my students

  6. Pingback: Palm Oil

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