Read Lipids definition, Lipid classification, Lipids functions, Phospholipids definition, Phospholipids classification, and Phospholipids functions
Lipids are organic substances relatively insoluble in water, soluble in organic solvents (alcohol, ether), actually or potentially associated with fatty acids, and are utilized by the body.
Lipids are classified into simple (fats and oils), complex (phospholipids, glycolipids), derived (fatty acids, steroid hormones), and miscellaneous (carotenoids).
Following are the function of lipids
- They’re the concentrated fuel reserve of the body (triacylglycerols).
- Lipids are the constituents of membrane structure and regulate membrane permeability (phospholipids and cholesterol).
- They function as a source of fat-soluble vitamins (A, D, E, and K).
- Lipids are important as cellular metabolic regulators (steroid hormones and prostaglandins).
- Lipids protect the interior organs, function as insulating materials, and provide shape and smooth appearance to the body.
These are complex or compound lipids containing phosphoric acid, in addition to fatty acids, nitrogenous bases, and alcohol.
Glycerophospholipids (or phosphoglycerides) contain glycerol as alcohol.
Sphingophospholipids (or sphingomyelins) contain sphingosine as alcohol.
Following are the function of Phospholipids
- In association with proteins, phospholipids form the structural components of membranes and regulate membrane permeability.
- Phospholipids (lecithin, cephalin, and cardiolipin) within the mitochondria maintain the conformation of electron transport chain components, and thus cellular respiration.
- Phospholipids participate in the absorption of fat from the intestine.
- Phospholipids are essential for the synthesis of various lipoproteins and thus participate in the transport of lipids.
- Accumulation of fat in the liver (fatty liver) is often prevented by phospholipids, hence they’re considered lipotropic factors.
- Arachidonic acid, an unsaturated carboxylic acid liberated from phospholipids, serves as a precursor for the synthesis of eicosanoids (prostaglandins, prostacyclins, thromboxanes, etc.).
- Phospholipids participate within the reverse cholesterol transport and thus help in the removal of cholesterol from the body.
- Phospholipids act as surfactants (agents lowering surface tension). For instance, dipalmitoylphosphatidylcholine is a crucial lung surfactant. Respiratory distress syndrome in infants is related to insufficient production of this surfactant.
- Cephalins, a crucial group of phospholipids participate in blood coagulation.
- Phosphatidylinositol is that the source of second messengers—inositol triphosphate and diacylglycerol, that are involved in the action of some hormones.
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