Fatty Acid

Fatty Acid:

Fatty acids are so named because some of them occur in fats. A fatty acid molecule is an unbranched chain of carbon atoms with each carbon atom ( C) forming four bonds to other atoms.It has a carboxyl group__ COOHat one end and hydrogen atom ( H) bonded to all or most carbon atoms, forming a hydrocarbon chain.


The carbon_ hydrogen bonds are nonpolar. Therefore, the hydrocarbon chain does not dissolve in water. The carboxyl group gives the molecule its acidic properties as it can dissociate into hydrogen ion (H+) and a negatively charged __ COO __ group. Because the carboxyl group contains the polar C= O and OH groups, it tends to dissolve in water even through the rest of fatty acid molecule will not. Dissociation cannot occur when the fatty acid is a part of a fat molecule, hence the name "neutral  fat." Water insolubility of lipids is due to the repulsion present between the nonpolar lipid  molecule and the polar water molecule. 

   Most fatty acids have an even number of carbon atoms between 14 and 22, mostly 16 or 18.

Fatty acids of two types:

1): Saturated 

In Satured fatty acids, all carbon atoms are interlinked by single bonds and each carbon atom carries a hydrogen atom. They cannot take up any more hydrogen, hence satured. The saturated fatty acids are straight chains. They have higher melting points and are solid at normal temperature. They have a general formula of CnH2nO2.They include palmitic acid, C16H32O2, and stearic acid, C18H36O2.Their melting points are 63.1°C and 69.6°C respectively. 

2): Unsaturated 

In Unsaturated fatty acids, two adjacent carbon atoms at one or more places lack hydrogen atoms and are interlinked by double bonds( C=C). They can take up additional hydrogen, hence unsaturated. These include 18_ carbon oleic, linoleic and linolenic acids and 20 _ carbon arachidonic acid. They have 1,2,3 and 4 double bonds respectively. 
Their general formula is CnH2n_2xO2.
Formula of oleic acid is C18H34O2,of linoleic acid is C18H32O2, of linolenic acid is C18H30O2,and of arachidonic acid is C20H32O2.
The unsaturated fatty acids have lower melting points ( 13.4°C for oleic acid), and are liquid at normal temperature. They are more abundant in the living organisms. Unsaturated fatty acids have a bend or kink at each double bond. The kinks make the fatty acid chains more disordered and hence more fluid at ordinary temperatures.

   The fatty acids having more than one double bonds are called polyunsaturated fatty acids. The oils having such fatty acids are termed Polyunsaturates.The latte are recommended by physicians for persons who have high blood cholesterol or cardiovascular diseases.Their use lowers the blood cholesterol level. Hydrogenation changes unsaturated fatty acids to saturated form and oil to a solid fat, e.g., vanaspati ghee, peanut butter and margarine¹.

Differences between saturated fatty acids and unsaturated fatty acids 

saturated fatty acids:

1):All carbon atoms are linked up by single bonds and bear hydrogen atoms.

2): Cannot take up more hydrogen. 

3): Are straight chains. 

4): Have higher melting point than unsaturated fatty acids. 

5): Are solid at ordinary temperature. 

6): Are less abundant in living organisms. 

7): Occur in most animal fats.

8): Increase blood cholesterol and cause arteriosclerosis.

Unsaturated fatty acids 

1): At one or more places, carbon atoms are joined by double bonds and lack hydrogen atoms.

2): Can take up more hydrogen. 

3): Have a bend at the double bond.

4): Have lower melting point than saturated fatty acids. 

5): Are liquid at ordinary temperature. 

6): Are more abundant in living organisms. 

7): Occur in most plant fats.

8): Lower blood cholesterol and donot cause arteriosclerosis. 

Structure and functions:

Structure Fatty Acids:

 Fatty acids are   biomolecules that consist of a long hydrocarbon chain with a carboxylic acid group at one end. They can very in chain length, typically ranging from 4 to 24 carbon atoms, and can have different degrees of saturation ( containing either single bonds or double bonds between carbon atom).Fatty Acid are composed of carbon chains containing a methyl group at one end and  a carboxyl group at the other. The methyl group is termed the omega and the carbon atom situated next to the carboxyl group is termed the "œ" carbon, followed by the " ß" carbon, etc. Fatty acid molecules also have two chemically distinct regions:

1): A long hydrophobic hydrocarbon chain, which is not highly reactive, 

2) A carboxyl ( _ COOH) group, which is hydrophilic and highly reactive. In the cell membrane, virtually all fatty acids form covalent bonds with other molecules via the carboxylic acid groups.


  Fatty acids can contain double bonds ( unsaturated fatty acids) or no double bonds ( saturated fatty acids) in the hydrocarbon chains. The presence of double bonds results in the formation of bonds or kinks in the molecules, and impacts the capacity of the fatty acid chains to stack together other differences between fatty acids include the length of the hydrocarbon chains, as well as the number and position of the double bonds.fatty acids having more than one double bonds are called polyunsaturated fatty acids. The oils having such fatty acids are termed Polyunsaturates.The latte are recommended by physicians for persons who have high blood cholesterol or cardiovascular diseases.Their use lowers the blood cholesterol level. Hydrogenation changes unsaturated fatty acids to saturated form and oil to a solid fat, e.g., vanaspati ghee, peanut butter and margarine¹ 

The three hydroxyl groups of a glycerol molecule join with the carboxyl groups of three fatty acids molecules to form a fat or glyceride molecules to form a fat or glyceride molecule. The chemical linkage between the glycerol and fatty acids is called the ester bond. It results from the elimination of three molecules of water ( condensation or dehydration). The fatty acids present as components of most of the animal fat are 16_ carbon palmitic acid and 18_ carbon stearic acid. The neutral fats formed with these fatty acids are named tripalmitin and tristearin respectively. Both are  pure fats. A fat having two molecules of palmitic acid and one molecule of stearic acid is termed dipalmito _ stearin ,and a fat having a molecule each of palmitic, oleic and stearic acid is called palmitio _ oleio_ stearin. These are mixed fats. 

The presence of the double_ bond will also influence the melting point as unsaturated fatty acids. The melting point is also influenced by weather there is an even or odd number of carbon atoms; an odd number of carbons is associated with a higher melting point.Futhermore, saturated fatty acids are highly stable, while unstructured fatty acids are more susceptible to oxidation. 

Function of Fatty Acids :

Fatty acids have important roles in 

1): Membrane structure: Fatty acids are a crucial component of cell membranes. They form a lipid bilayer alongside other lipids, such as phospholipids and cholesterol, providing structure and fluidity to the cell membrane. 

 2): Energy storage: Fatty acids are a highly efficient and concentrated source of energy. They can be metabolized in the body, providing a much higher yield of energy compared to carbohydrates or proteins.

3): Insulation and protection: Fatty Acids can be found in adipose tissue, where they function as insulation and protection for organs and tissues against mechanical shock.

4): Precursor for signaling molecules: Certain fatty acids, particularly those containing double bonds, can serve as precursors for the synthesis of signaling molecules called elcosanoids. These include prostaglandins, thromboxanes, and leukotrienes, which play essential roles in inflammation, blood clotting, and immune responses. 

5): Vitamin absorption: certain types of fatty acids, such as long _ chain fatty acids, help with the absorption and transport of fat _ soluble vitamins,  including vitamins A, D,  E, and K.

6): Brain Development  and Function:
Fatty acids, particularly omega,_ 3 and omega_ 6 fatty acids, play a vital role in brain development and function. These are essential for the growth and maintenance of neural structures and can influence cognitive abilities and mood.

7): Thermal regulation: Fatty acids in brown adipose tissue can be broken down to produce heat, which helps regulate body temperature in newborns and animals that hibernate .

8) Carbohydrate : Carbon skeleton of monosaccharides is used in the formation of fatty acids, chitin , cellulose etc.

Overall fatty acids are essential compounds that perform diverse functions in the body, including energy  storage, membrane structure, signaling, insulation, thermal regulation, vitamin absorption, and brain development. 

Example of Fatty acids:
Saturated fatty acids and unsaturated fatty acids. Unsaturated fatty acids are found in fish oil and vegetable oil. Only coconut oil and palm oil are the example of saturated oil.

9.3 kilo energy is liberated from 1 gram fat.

Normally an adult person should get 20_ 30% of energy from fat. Fat store maximum energy per gram.


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