Let us learn about Fatty Acids. After reading this article you will learn about: 1. Subject-Matter of Fatty Acids 2. Function or Uses of Lipids.
Subject-Matter of Fatty Acids:
Fatty acids are compounds consisting of a long hydrocarbon chain with a carboxylate group at one end. The general formula is CH3 (CH2)n COOH.
They are obtained from the lipids of most plants and animals and have the following characteristics:
(i) They are usually monocarboxylic acids, R-CO2H.
(ii) They possess an even number of carbon atoms.
(iii) The R group is usually an un-branched chain.
(iv) The R group may be saturated, or it may have 1, 2, or 3 double bonds.
Fatty acids are divided into 2 classes depending upon whether or not the carbon chain carries the maximum possible number of attached hydrogen’s.
If all carbon atoms are fully saturated h with hydrogen, the fatty acid is called saturated and has the structure like:
The most abundant saturated fatty acids are palmitic acid, CH3(CH2)14 COOH, and stearic acid, CH3(CH2)16 COOH. These and some other acids along with glycerol form the bulk of the body fat in most organisms.
When all the carbon atoms are not fully saturated with hydrogen, they are joined by double bonds and the fatty acid is called unsaturated:
Typical unsaturated fatty acids are oleic acid, CH3(CH2)7 CH = CH (CH2)7 COOH or C17H33COOH and linoleic acid CH3(CH2)4CH = CHCH2CH = CH(CH2)7COOH. Linoleic acid has more than one carbon-carbon double bond and is thus polyunsaturated.
Their chemical structure is as follows:
The melting point of a fatty acid depends on its nature or kind, the greater the degree of unsaturation, the lower the melting point. For example, the melting point of the stearic acid (saturated) is 70° C and that of oleic acid (one double bond) and linoleic acid (2 double bonds) is 4°C and -5°C respectively. For this reason, most animal fats are solids and most vegetable oils are liquids at room temperature.
The oils are more unsaturated than the fats because they are composed of the glycerides of unsaturated fatty acids. The hydrogenation of the double bonds of the fatty acid present in oils (converting them into saturated acids) raises the melting point of the glycerides.
The “hardening” of vegetable oil such as the cotton seed or groundnut oil is an important commercial process by which the cooking fats like “Dalda”, etc., are produced.
Function or Uses of Lipids:
Fats and fatty acids are important food storage compounds in most organisms. The fat is stored in the adipose tissue. Like carbohydrates and proteins, fats also play significant role as structural component of cells. For example, certain phospholipids form an important component of the cell membranes and of enzyme systems in the mitochondria.
Phosphatides have also been considered essential for the formation of one of the blood clotting factors. Phospholipid cephalin helps in the formation of prothrombinase which converts prothrombin into thrombin during blood coagulation. Some complex lipids are also found in the brain and nerve tissue and in the heart and skeletal muscles. Besides, the oxidation of fats provides a large amount of energy to body cells.
The animal fats are the most important source of some of the vitamins, i.e., A and D. The steroids are also of great physiological importance and the cholesterol is the main precursor of steroid hormones, (e.g., estrogen progesterone, corticosterone) which affect cellular activities by influencing gene expression. Some steroids are vitamins (e.g., vitamin D2) and influence the activities of certain cellular enzymes.
Other steroids are regular constituents of membranes, where they influence membrane structure, permeability and transport.