Fatty Acids
Fatty acids are building block of most lipids, made of long chain organic acids having one polar
carboxyl group (head) and a non-polar hydrocarbon chain (tail). The latter makes them water
insoluble. They are not found free in nature but found as esterified forms. Most naturally occurring
fatty acids have got even number of carbons. They may be saturated or unsaturated, with one or
more double bonds. Mostly the double bond occurs at the 9th carbon as we count from the
carboxyl group end.
There are two systems of numbering the carbon atoms in a fatty acid
- Numbering starts from carboxyl carbon. The last carbon is the "n" carbon
- The second carbon is the "α"and the third the "β" Carbon. The last carbon atom is omega.
Eg:- CH3 (CH2)7 CH=CH (CH2)7 COOH oleic acid (Unsaturated fatty acid)
Fatty acids can be represented as shown below where the delta indicates the position of the
double bond and the next number shows the number of carbon atoms and the last number
indicates the number of double bonds. In a different way the position of the double bond(s) can
be indicated as shown in the second expression without the delta.
C18:1, ∆9
or 18:1(9)
C18 indicates 18 carbons, 1 indicates the number of double bonds, delta 9(∆9
) indicates the
position of double bond between 9th and 10th carbon atoms.
- Double bonds in naturally occuring fatty acids are in the cis- configuration and saturated fatty
acids of C12 to C24 are solids at body temperature but the unsaturated once are liquids.
PUFA (Polyunsaturated fatty acids): They have two or more double bonds .they are called as
essential fatty acids because they are required in the body and cannot be synthesized. So they
need to be include in the diet.
18 Linoleic acid 18: 2; 9 (12)
18 Linolenic acid 18: 2; 9 (12, 15)
These two are called essential fatty acids.
20 Arachidonic acid 20: 4; (5, 8, 11, 14)
Arachidonic acid is semi essential fatty acid because it can be synthesized from the above two
essential fatty acids.
Functions:
- The fluidity of membrane depends on length and degree of unsaturated fatty acids. Membrane PL contains essential fatty acids. In case of deficiency of EFA, other fatty acids replace them in the membrane; as a result membrane gets modified structurally and functionally.
- They are required for the synthesis of PL, cholesterol ester and lipoproteins
- Poly unsaturated fatty acids are released from membranes, diverted for the synthesis of prostaglandins, leukotriens and thromboxanes.
- They act as fat mobilizing agents in liver and protect liver from accumulating fats (fatty liver)