Lipid- Defination Classification Fuction Structure with All Example-

Lipids-

Biological Lipids are a chemically diverse group of organic compound which are insoluble or only poorly soluble in water.
They are readily soluble in non' polar solvent such as ether, chloroform or benzene.the hydrophobic nature of Lipids is due to the predominance of hydrocarbon chains ( -CH2-CH2-CH2- )in their structure. Unlike the protein, nucleic acids and polysaccharide, Lipids are not Polymer.

Lipid- Defination Classification Fuction Structure with All Example

Functions-

Biological lipids have diverse functions. The four general functions of biological lipids have been identified.

1- They serve as a storage form of metabolic fuel.
2- They serve as a transport form of metabolic fuel.
3-They provide the structural components of membranes.
4-They have protective functions in bacteria, plants, insects, and vertebrates, serving as a part of the outer coating between the body of the organism and the environment.

Fatty acids-

stituents in a large (Fatty acids are the simplest form of lipids and serve as constituents in a large number of complex forms of lipids.
Fatty acids are long-chain hydrocarbons (4 to 36 carbons long) with one carboxyl group. Fatty acids in biological systems usually contain an even number of carbon atoms. The 16- and 18-carbon fatty acids are most common.
The alkyl chain may be saturated or unsaturated) Unsaturated fatty acids may contain one or more double bonds. Fatty acids are amphipathic by nature; that is, they have both nonpolar and polar ends.

Structure of fatty acid- fig..1

Saturated and unsaturated fatty acids-

Saturated fatty acids have no double bonds in the chain. Their general formula is CH,-(CH2),-COOH where n specifies the number of methylene groups between the methyl and carboxyl carbons. Examples of predominant saturated fatty acids are lauric, myristic, palmitic and others.

Essential fatty acids-

Mammals lack the enzymes to introduce double bonds at carbon atoms beyond C-9 in the fatty acid chain. Hence, mammals cannot synthesize linoleate and linolenate.
Linoleate and linolenate are the two essential fatty acids. The term essential means that they must be obtained from the diet because they are required by an organism and cannot be endogenously synthesized. Fatty acids that can be endogenously synthesized are termed as nonessen- tial.
They are nonessential also in the sense that they do not have to be obligatorily included in the diet.

Melting point of fatty acids-

The melting point of fatty acids depend on chain length and degree of unsaturation. The longer the chain length, the higher the melting point and the greater the number of double bonds, the lower the melting point. The presence of double bonds makes unsaturated chain more rigid. As a result, unsaturated chains cannot pack themselves in crystals efficiently and densely as saturated chain,
so, they have lower melting point as compared to saturated fatty acids. Similarly, the unsaturated fatty acids with cis configuration have lower melting points than the unsaturated fatty acids with trans configuration.

Triacylglycerol and Wax-

Triacylglycerols (also called triglycerides) are triesters of fatty acids and glycerol. They are composed of three fatty acids and a glycerol molecule. Triacylglycerols are of two types - simple and mixed type. Those containing a single kind of fatty acids are called simple triacylglycerols and with two or more different kinds of fatty acids are called mixed triacylglycerols. The general formula of triacylglycerol is given below:

Genral structure of triacylglycerol

Triacylglycerols are nonpolar, hydrophobic in nature and a major form of stored lipids. Because triacylglycerols have no charge (i.e. the carboxyl group of each fatty acid is joined to glycerol through a covalent bond), they are sometimes referred to as neutral lipid.
Triacylglycerol molecules contain fatty acids of varying lengths, which may be unsaturated or saturated. Triacylglycerols can be distinguished as fat and oil on the basis of physical state at room temperature. Fats, which are solid at room temperature, contain a large proportion of saturated fatty acids. Oils are liquid at room temperature because of their relatively high unsaturated fatty acid content. Hydrolysis of triacylglycerols with alkalis such as NaOH or KOH is called saponification.
Saponification yields salts of free fatty acids (termed soap) and glycerol. The number of milligrams of KOH required to saponify one-gram of fat is known as saponification number. The saponification number measures the average molecular weight of fats.
Similarly, the number of grams of iodine that can be added to 100g sample of fat or oil is called iodine number, which is used to determine the degree of unsaturation (i.e. extent of unsaturation).

Waxes-

Natural waxes are typically esters of fatty acids and long chain alcohols. They are formed by esterification of long chain fatty acids (saturated and unsaturated) and high molecular weight monohydroxy alcohols (C14 to C36). Waxes are biosynthesized by many plants or animals. The best known animal wax is beeswax. Triacontanoylpalmitate (an ester of palmitic acid with the alcohol triacontanol) is the major component of beeswax.

The general structure of waxes

Phospholipids-

A phospholipid is an amphipathic molecule constructed from four components: fatty acids, a platform to which the fatty acids are attached, a phosphate and an alcohol attached to the phosphate. The platform on which phospholipids are built may be glycerol or sphingosine.

Phospholipids are amphipathic molecules consist of a polar head and unsaturated fatty acid tails.
The unsaturation in the fatty acid chains prevents the close packing of the plasma membrane.

Phosphoglycerides-

Phospholipids derived from glycerol are called phosphoglycerides (orglycerophospholipids). A phosphoglyceride consists of a glycerol molecule, two fatty acids, a phosphate, and an alcohol (e.g. choline). Phosphoglycerides are the most numerous phospholipid molecules found in cell membranes.
In phosphoglycerides, the hydroxyl groups at C-1 and C-2 of glycerol are esterified to the carboxyl groups of the two fatty acid chains. The C-3 hydroxyl group of the glycerol backbone is esterified to phosphoric acid. When no further additions are made, the resulting compound is phosphatidic acid, the simplest phosphoglyceride. Phos- phatidic acids are found in small amount in most natural systems. The major phosphoglycerides are derived from phosphatidic acid by the formation of an ester bond between the phosphate group and the hydroxyl group of one of several alcohols. The common alcohol moieties of phosphoglycerides are serine, ethanolamine, choline, glycerol, and the inositol. If the alcohol is choline, the phosphoglyceride molecule is called phosphatidylcholine (also referred to as lecithin) and if serine then it is called phosphotidylserine.

Ether glycerophospholipids-

Ether glycerophospholipids possess an ether linkage instead of an acyl group at the C-1 position of glycerol. One very common example of ether glycerophospholipid found in mammals is platelet activating factor or PAF. PAF is a potent signal molecule that causes platelet aggregation and dilation of blood vessels. In ether glycerophospholipids, the ether-linked chain may be saturated or may contain a double bond between C-1 and C-2. Ether glycerophospholipids in which the alkyl moiety is cis-a,ß-unsaturated is termed as plasmalogen.

Glycolipids-

Lipid containing saccharide groups go under the general name of glycolipids. The glycosphingolipid is the most important type of glycolipid and constitute third major class of membrane lipids. In glycosphingolipid head group contains one or more sugars connected directly to the -OH at C-1 of the ceramide moiety (do not contain phosphate).

Sphingolipid storage disease-

A group of inherited metabolic disorders characterized by an excessive intra-lysosomal deposition of sphingoglycolipids and sphingophospholipids. Clinical features vary with the specific subtype of the disease. Examples of selected sphingolipid storage diseases are given below:

Sphingolipid storage diseases

Disease Accumulating sphingolipid Enzyme deficiency

Tay-Sachs Ganglioside GM2 B-Hexosaminidase A

Gaucher's Glucocerebroside B-Glucosidase

Niemann Pick Sphingomyelin Sphingomyelinase

Fabry's Trihexosylceramide a-Galactosidase

Krabbe's Deacylated galactocerebroside A Galactocerebrosidase

Steroid-

Steroids are complex derivatives of triterpenes. Each type of steroid is composed of four fused rings called steroids nucleus. A sterol is a class of steroid characterized by a hydroxyl group at C-3. Cholesterol is an example of the sterol and an essential component in animal cell membranes. Cholesterol acts as a precursor for the biosynthesis of all steroid hormones and bile salts. Cholesterol is usually stored within cells as a fatty acid ester. Cholesterol is not found in plants and fungi. Types of sterol that is common in plants are stigmasterol, sitosterol and campesterol. Ergosterol is a sterol present in the cell membrane of fungi.

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