Role Lipids perform several biological functions, such as:
1) Storage: They are storage compounds and in the animal body, they reserve energy in the form of triglycerides in adipocytes.
2) Energy Source: As energy source, they provide 9kcal of energy per gram. The per unit weight of fats supply two times more energy as compared to per unit weight of proteins or carbohydrates.
3) Cell Membranes: They are important components of the cell membrane. Phosphoglycerides, sphingolipids, and steroids are structural components of cell membranes.
4) Membrane Permeability: They regulate membrane permeability.
5) Vitamins: They serve as a source for fat-soluble vitamins (A, D, E, and K). Therefore, lipids are essential for the effective absorption of fat-soluble vitamins from the intestine.
6) Electrical Insulation: They act as electrical insulators to the nerve fibres, where the myelin sheath contains lipids.
7) Enzyme Systems: They are components of various enzyme systems.
8) Cellular Metabolic Regulators: Some lipids like prostaglandins and steroid hormones act as cellular metabolic regulators.
9) Signalling: Being small and insoluble in water, they act as signalling molecules.
10) Thermal Insulation: Fat deposited in the subcutaneous layer provides insulation and protection from cold.
11) Fluidity and Flexibility: Polyunsaturated phospholipids are important constituents of phospholipids, They provide fluidity and flexibility to the cell membranes.
12) Transport: Lipoproteins transport cholesterol and triglycerides from their origin to sites of use or uptake (e.g., the liver, muscle, and fat tissue). Lipoproteins that are complexes of lipids and proteins occur in blood as plasma lipoprotein.
13) Essential Fatty Acids: They also supply the essential fatty acids which are not synthesised in the human body but are required for normal growth. Essential fatty acids (like linoleic and linolenic acids) are the precursors of many different types of eicosanoids including prostaglandins and thromboxanes. These play important role in pain, fever, inflammation, and blood clotting.
14 Cholesterol :is found in cell membranes, blood, and bile of many organisms. It maintains the fluidity of membranes by interacting with lipid complexes. It is the precursor of bile acids, Vitamin D, and steroids.
15) Steroid Hormones: They are the critical intercellular messengers.
In the table a summary of various types of lipids and their biological role is given:
Lipids and their Biological Roles:
Types of Lipids
fatty acids
Principal building blocks of complex lipids.
Waxes
Esters of fatty acids (heat sensitive) and also act as moisture barrier.
Triacylglycerols
Membrane precursors and stores energy (of fats and oils).
Glycerophospholipids
Membrane componenis.
Sphingolipids
Form brain lipids and membrane components.
Steroids
Cholesterol, bile salts, and steroid hormones perform various functions.
Terpenes
Turpentine has many roles,
Phospholipids
Form membrane components.
Eicosanoids
Signalling molecules (prostaglandin).
Sphingomyelins
Form membrane components (important in myelin sheaths).
Glycospingolipids
Cell recognition (ABO blood group antigen).
Steroids (sterols)
Form membrane components and hormones.
Lipid vitamins
Vitamin A, E, and K are important.
Carotenoids
Photosynthetic accessory pigments.
Chlorophyll
Major light harvesting pigment.
Essential oils
Menthol, limonene, terpenene, myrcene, saninene, etc., play major roles.
Plastoquinone/ubiquinone
Lipid soluble electron cariers.
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