· LIPID describes a chemically varied group of organic fatty compound substances
· Lipids are highly concentrated energy stores.
· They are water-insoluble bio-molecules but soluble in organic solvents such as ether, benzene. Chloroform, etc. (lipophilic).
· Lipids serve as fuel molecules, signal molecules, and components of membranes, hormones and intracellular messengers.
· They are esters of long chain fatty acids and alcohols.
· Only a limited number of lipids are clinically important. This group includes fatty acids, triacylglycerols (or triglycerides), cholesterol, and phospholipids.
· The various types of lipids differ in their chemical and physical properties and in their physiological roles.
· Other lipids serve as precursors for other essential compounds or act as a sources or storage of energy.
· Lipids are important insulators against heat loss and organ damage and allows for nerve conduction in the central nervous system.
· When conjugated with proteins, lipids compounds are called lipoproteins, the transport form of lipids in aqueous substances such as blood.
Classification Of Lipids:
LIPIDS are classified broadly according to their chemical composition into:
1- simple lipids
2- complex lipids
3- derived lipids
4- miscellaneous lipids based.
Classification Scheme:
Functions of Lipids:
Classification Of Lipids:
Based on their Biological functions Lipids can be classified into:
Storage Lipids—The principle stored form of energy
Structural Lipids– The major structural elements of Biological Membranes
Lipids are signals, cofactors and pigments
Storage Lipids:
Storage Lipids include fats and oils, and wax.
Fats and oils are composed of 3 fatty acids each in ester linkage with a single glycerol (Triacylglycerols)
3FA+Glycerol=Fats, Oils
Waxes are esters of long-chain(C14-C36) saturated and unsaturated fatty acids with long chain (C16-C30) alcohols
FA + Alcohol = waxes
Fatty Acids:
• Fatty acids are composed only of carbon, hydrogen and oxygen
• Fatty Acids are carboxylic acids with hydrocarbon chains ranging from 4-36.
• Fatty acids are of 2 types: Saturated and Unsaturated.
Triacylglycerols (TAG)
Triacylglycerol(Triglyceride) is an ester of glycerol with three fatty acids.
It is also called neutral fat.
They are stored in adipocytes in .
A mammal contains 5% to 25% or more of its body weight as lipids,90%TAG
Wax:
Waxes are esters of long chain (C14-C36) saturated and unsaturated fatty acids with long chain (C16-C30) alcohols.
Functions of Wax:
Chief storage fuels for some of the microorganisms.
Protect skin and hair.
Application in industries, pharmaceuticals, and cosmetics
Cholesterol
Cholesterol is a derived lipid. Its widely distributed as sterols in animals and humans, most of which is synthesized by the liver
It is an essential component of cell membrane
Vit. D, hormones and bile acids are synthesized from cholesterol.
Bile acids are essential for normal digestion and absorption of fats and fat-soluble vitamins.
An increase in dietary intake of cholesterol increases its synthesis in the body as well which leads to coronary heart diseases.
Unsaturated fats reduce the level of cholesterol in blood.
LDL, HDL AND VLDL:
Low density lipoproteins (LDL) transports cholesterol from liver through blood to the tissues (Bad cholesterol)
High density lipoprotein (HDL) transports cholesterol from blood to the liver where it is metabolised (Good cholesterol)
LDL high Cholesterol high High risk of heart attack
HDL high Cholesterol low Low risk of heart attack
Bile Acids:
Essential fatty acids:
Linoleic, Linolenic, and Arachidonic acids
Essential fatty acids synthesize structural fats in tissues such as prostoglandins, leukotriens, prostocyclins, thromboxane which regulate body functions such as blood clotting, inflammation etc.
Essential fatty acid deficiency can result in abnormalities like poor growth, increase food intake, scale inflammation of skin and impaired immune response.
Best dietary sources are vegetable oils(corn oil, sunflower oil) and oil rich fish (Herring , Sardine)
Trans Fatty Acids:
Exist in very small amounts in natural foods. Trans fatty acids lowers HDL level and raises total blood cholesterol
They also raise plasma conc. Of lipoprotein – anthrogenic lipoprotein.
Trans fatty acids are formed when vegetable oils are hydrogenated during the formation of margarine etc.
Lipids as Biochemical Markers of Disease