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The chemical, structural and physical characteristics or properties of the biological lipids are as under:
(i) The fats and oils are stored forms of energy in living organisms and are highly reduced compounds.
(ii) The complete oxidation of fatty acids into CO2 and H20 in cells is highly exergonic or energy producing in the same way as the explosion of fuels in the internal combustion engines.
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(iii) The fatty acids are hydrocarbon derivatives or carboxylic acids with hydrocarbon chains of 4 to 36 carbons.
(iv) The nonpolar hydrocarbon chain accounts for the poor solubility of fatty acids in water.
(v) Triacylglycerol’s also called triglycerides, fats or neutral fats are fatty acid esters of glycerol.
(vi) Triacylglycerol’s provide stored energy and insulation.
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(vii) Most of the natural foods contain triacylglycerol’s.
(viii) The ester linkages of triacylglycerol’s are susceptible to hydrolysis by either acid or alkali Na+ and K+ salts of fatty acids are known as soaps. The practical application of the soaps is for their ability to solubilize or disperse water insoluble materials by forming microscopic aggregates called micelles.
(ix) Biological waxes are esters of long chain saturated and unsaturated fatty acids which serve as energy stores and water impermeable coatings.
(x) The lipids form the structure of biological membranes. The biological membranes comprise of a double layer of lipids serving a barrier to the passage of polar molecules and ions.
There are 3 general types of membrane lipids, which are:
(1) Glycerophospholipids in which hydrophobic regions are composed of two fatty acids joined to glycerol,
(2) Sphingolipids in which a single fatty acid is joined to a fatty amine, and
(3) Sterols or the compounds characterized by a rigid system of four fused hydrocarbon rings.
(xi) Some animals and unicellular organisms are rich in ether lipids.
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(xii) Sphingolipids, the second largest class of membranes lipids, are derivatives of sphingosine.
(xiii) Sphingolipids are the sights of biological recognition.
(xiv) Specific phospholipases degrade membrane phospholipids.
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(xv) Sterols have four fused hydrocarbon rings.
(xvi) Amphipathic lipids or the lipids containing both polar and nonpolar domains, form aggregates.
(xvii) The steroid hormones carry messages between tissues. Major groups of steroid hormones are the male and female sex hormones and the hormones of the adrenal cortex, Cortisol and Aldosterone.
(xviii) The hydrolysis of phosphatidylinositol produces intracellular messengers.
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(xix) Ericosanoids which are fatty acid like derivatives with a variety of extremely potent hormone like actions on various tissues of vertebrate animals are potent biological effectors.
(xx) Vitamins A, D, E and K are fat soluble
(xxi) Liquid quinones carry electrons.
(xxii) Dolichols form activated hydrophobic sugar derivatives.
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(xxiii) Lipid extraction requires organic solvents.
(xxiv) Adsorption chromatography separates lipids of different polarity.
(xxv) Gas-liquid chromatography resolves mixtures of volatile lipid derivatives.
(xxvi) Specific hydrolysis is useful in determination of lipid structure.
