Lipids

   The lipids are the heterogeneous group of compounds related to fatty acids. The Lipids are soluble in an organic solvent but insoluble in water, Show these are hydrophobic compounds and are composed of carbon, hydrogens, and oxygen as carbohydrates. However, these have relatively less oxygen in proportion as compared to carbohydrates. Due to the high proportion of carbon and hydrogen lipids store double the amount of energy as compared to carbohydrates. For example, triasterin has a molecular formula C57H110O6. it is simple lipid. Lipids provide insulation against atmospheric pressure and also act as waterproof material as insoluble in waterproof. lipids are an important part of the cell membrane of fell. Some lipids are also hormones. for example cutin an additional protective layer on the cuticle of the epidermis and waxes in the exoskeleton of insects. These have a specific gravity of  0.8. These cannot be crystallized except steroids. Examples of lipids are glycerine, phospholipids, steroid, and waxes.

Acylglyceroids:

      The most abundant lipids in living cells are acylglycerols. These are chemically composed of esters of glycerol and fatty acids. The most important acyl glyceride is triacylglyceride which is also called neutral lipid. Ester is produced as the result of a chemical reaction of alcohol with an acid and a water molecule realised such a reaction is called esterification.

• Glycerol is a trihydroxy alcohol that contains three carbon sach of which bear one OH group. 
• Fatty acids are the more important part of acyl glyceride. These contain an even number of carbon atoms from 2-30, in a straight chain associated with a COOH group. These may contain no double bond or up to 6 double bonds. If fatty acids have no double bond then these are called saturated fatty acids. And if these contain at least a single double bond, then these become unsaturated fatty acids.

In animals, the fatty acids are straight in the chain, while in plants, these are branched or ringed. About 30 fatty acids are found. These vary in length. Acetic acid and butyric fatty acids are the simplest fatty acids, while palmetric and steric acids are the most common fatty acids. Fats containing unsaturated fatty acids are usually liquid at room temperature and I said to be oil and these are important in plants while the fats which contain saturated fatty acids are solid at room temperature and important in animals. Fats are lighter than water and these have specific gravity. The solubility of fatty acids in organic solvents and their melting point are increased with the increasing number of carbon atoms in the fatty acid chain. for example, palmitic acid which contains 16 carbon is much more soluble in organic solvents than butyric acids (4C), and the melting point of palmitic acid is 63.1 centigrade as against - 8 centigrade for butyric Acid. While oleic acid is unsaturated as it contains one double bond at the 9th carbon while linoleic acid is also unsaturated as it also contains 18 carbons, like stearic acid( which is saturated) and oleic acid, but it has two double bonds. Triglycerides contain hydrocarbon change which melts at a low temperature and is useful for living things.

Phospholipids:

       These are derivatives of phosphatidic acids which are compounds of glycerol, fatty acids, and phosphoric acid. Phosphotadic acid is combined with any nitrogenous base or amino alcoholic to form phospholipids. These are:

1 choline ( a nitrogenous base)

2 Serine  ( amino acid)

3  Ethanolamine  (amino alcohol)

4 Inositol  (amino alcohol)

These are an important part of phospholipids. The phospholipids are frequently widespread in bacteria, animal, and plant cells and are associated with the membranes. Phosphatidylcholine is an example of a phospholipid. It is also called lecithin in which choline is attached to a phosphate group. One end of the phospholipid molecule which contains the phosphate group is hydrophilic while the other end which contains fatty acid is hydrophobic. And these are important parts of the cell membrane. The phosphatidic acid is most similar to diglyceride as it contains glycerol, two fatty acids esterified with the first and second OH groups of glycerol, and a phosphate group esterified with the OH group of glycerol at which nitrogenous base is attached. 

Sphingolipids are found in membranes of both plant and animal cells. 

Waxes:

Waxes are highly hydrophobic compounds that provide a protective coating on fruit and lead. Some insects also secrete waxes. Natural waxes are simple lipids chemically waxes are composed of long chains of fatty acids and alkane and alcohol. for example cutin on the leaves of plants. These are chemically inert and resistant to atmospheric oxidation. These provide protective functions in plants and animals. Waxes protect from water loss and from damage. These also provide water barriers for insects, birds, and animals such as sheep.

Synthetic waxes are generally derived from petroleum or poly theme. for example, paraffin wax which is used to make candles

Terpenoids:

       These are very large and synthesized form from a five-carbon buildings simple unit known isoprene unit. These units condense in different ways to form rubber, carotenoids, steroid, and terpenes. Two isoprene units form monoterpene( menthol), four form diterpenes ( vitamin A, phytol), and six form triterpene (amber). Natural rubber is made up of many terpenes.

Steroids:

   These are only those which can be crystallized. These are the lipids of high molecular weight. A single steroid consists of 17 carbon atoms arranged in 4 attached rings three of which contain six carbon while one contains 5 carbon atoms. These are also manufactured from isoprene units. examples of Steroid cholesterol which is the precursor of a large number of equally important steroids include bio acid male sex hormone testosterone, female sex hormone progesterone, and estrogen, bile salts melt by fat, and Vitamin D which helps to regulate calcium metabolism are also steroids.

Prostaglandins:

 These are found in every mammalian tissue and act as local hormones and are derived from arachidonic acid. Some of these reduce blood pressure, and some raise it. These are also involved in inducing fever and inflammation and also intensify the sense of pain. These also help in the aggregation of the platelet. The ability of Aspirin to reduce fever and decrease pain depends upon its ability to inhibit prostaglandin synthesis.