Lipids are essential macromolecules found in all living cells, lacking specific monomer units.
They are heterogeneous compounds, insoluble in water but soluble in organic solvents (e.g., chloroform).
Common types include fats, oils, steroids, and waxes.
Lipids play critical roles in metabolism and health, implicated in conditions like obesity and cardiovascular diseases.
Biological Functions of Lipids
Dietary components with high energy value and sources of fat-soluble vitamins.
Serve as energy stores and insulation in organisms.
Integral components of plasma membranes and involved in signaling processes.
Classification of Lipids
Simple Lipids: Esters of fatty acids and alcohol, yielding fatty acids and alcohol upon hydrolysis (examples: fats, oils, waxes).
Complex Lipids: Contain additional compounds like sugars and phosphoric acid, yielding multiple products upon hydrolysis (examples: phospholipids, glycolipids).
Derived Lipids: Hydrolysis products from simple and complex lipids, including fatty acids and steroids.
Fatty Acids
Long carboxylic acids, existing primarily as esters in fats and oils.
Can be saturated (no double bonds) or unsaturated (one or more double bonds).
Common saturated fats: palmitic acid (C16), stearic acid (C18).
Monounsaturated (e.g., oleic acid) and polyunsaturated fatty acids (e.g., linoleic, linolenic acids) are essential because they cannot be synthesized by the body.
Eicosanoids
Derived from polyunsaturated fatty acids, acting as local hormones involved in various physiological functions (e.g., inflammation).
Classes include prostanoids and linear eicosanoids.
Triacylglycerols
Major form of fats for energy storage in living organisms, releasing 9 kcal/g when metabolized.
Efficient energy storage compared to carbohydrates.
Steroids
Cholesterol is a key steroid, a precursor for hormones and bile acids.
Steroids have a common cyclic structure and various biological roles.
Lipoproteins
Transport lipids in aqueous environments such as blood.
Classified into HDL (good cholesterol, promotes cholesterol excretion) and LDL (bad cholesterol, deposits cholesterol in tissues).
Physical Properties of Lipids
Insoluble in water, soluble in non-polar solvents (e.g., ether, benzene).
Viscous texture; can be liquid or solid at room temperature.
Chemical Properties of Lipids
Hydrolysis: Lipids can be broken down into fatty acids and glycerol.
Saponification: Formation of soap from lipid hydrolysis.
Rancidity: Deterioration resulting from oxidation or hydrolysis of fats.
Summary of Lipid Chemistry
Lipids are diverse compounds crucial for biological functions, energy storage, and cellular structure.