LIPIDS
INTRODUCTION
Lipids are a broad group of naturally occurring organic compounds that are
insoluble in water but soluble in non-polar organic solvents such as ether,
chloroform, and benzene. They include fats, oils, waxes, phospholipids, glycolipids,
and sterols. Structurally, most lipids contain long-chain fatty acids esterified with
alcohols (commonly glycerol). Nutritionally, lipids serve as a major energy reservoir,
providing 9 kcal/g, and play essential roles in cell membrane integrity, hormone
synthesis, fat-soluble vitamin absorption, and thermal insulation. Their
hydrophobic nature allows them to form biological membranes and signalling
molecules that regulate metabolic and physiological functions.
CLASSIFICATION OF LIPIDS
Simple Lipids
Simple lipids include fats and oils (triglycerides) formed by esterification of fatty
acids with glycerol, and waxes formed by esterification of fatty acids with long-
chain alcohols.
Compound (Complex) Lipids
These include phospholipids, glycolipids, and lipoproteins. Phospholipids contain
fatty acids, glycerol, phosphate, and nitrogenous bases, forming structural
components of cell membranes. Glycolipids contain fatty acids, sphingosine, and
carbohydrate residues, important in nerve tissue.
Derived Lipids
Derived lipids include fatty acids, glycerol, steroids, sterols (cholesterol), fat-soluble
vitamins (A, D, E, K), prostaglandins, and other lipid-derived signalling molecules.
PHYSICAL PROPERTIES OF LIPIDS
, Lipids are hydrophobic or amphipathic (in phospholipids), and their
solubility depends on the length and saturation of fatty acids.
Solid fats contain higher proportions of saturated fatty acids, while oils
contain unsaturated fatty acids with lower melting points due to double
bonds causing kinks.
Lipids have lower specific gravity than water and exhibit emulsification in
the presence of bile salts.
They are colourless or slightly yellow, non-volatile, and exhibit optical
activity depending on their fatty acid composition.
CHEMICAL PROPERTIES OF LIPIDS
Hydrolysis (Saponification)
Triglycerides undergo hydrolysis in the presence of alkali, producing glycerol and
soap (salts of fatty acids).
Acid Hydrolysis
Hydrolysis in presence of HCl or H₂SO₄ forms free fatty acids and glycerol.
Hydrogenation
INTRODUCTION
Lipids are a broad group of naturally occurring organic compounds that are
insoluble in water but soluble in non-polar organic solvents such as ether,
chloroform, and benzene. They include fats, oils, waxes, phospholipids, glycolipids,
and sterols. Structurally, most lipids contain long-chain fatty acids esterified with
alcohols (commonly glycerol). Nutritionally, lipids serve as a major energy reservoir,
providing 9 kcal/g, and play essential roles in cell membrane integrity, hormone
synthesis, fat-soluble vitamin absorption, and thermal insulation. Their
hydrophobic nature allows them to form biological membranes and signalling
molecules that regulate metabolic and physiological functions.
CLASSIFICATION OF LIPIDS
Simple Lipids
Simple lipids include fats and oils (triglycerides) formed by esterification of fatty
acids with glycerol, and waxes formed by esterification of fatty acids with long-
chain alcohols.
Compound (Complex) Lipids
These include phospholipids, glycolipids, and lipoproteins. Phospholipids contain
fatty acids, glycerol, phosphate, and nitrogenous bases, forming structural
components of cell membranes. Glycolipids contain fatty acids, sphingosine, and
carbohydrate residues, important in nerve tissue.
Derived Lipids
Derived lipids include fatty acids, glycerol, steroids, sterols (cholesterol), fat-soluble
vitamins (A, D, E, K), prostaglandins, and other lipid-derived signalling molecules.
PHYSICAL PROPERTIES OF LIPIDS
, Lipids are hydrophobic or amphipathic (in phospholipids), and their
solubility depends on the length and saturation of fatty acids.
Solid fats contain higher proportions of saturated fatty acids, while oils
contain unsaturated fatty acids with lower melting points due to double
bonds causing kinks.
Lipids have lower specific gravity than water and exhibit emulsification in
the presence of bile salts.
They are colourless or slightly yellow, non-volatile, and exhibit optical
activity depending on their fatty acid composition.
CHEMICAL PROPERTIES OF LIPIDS
Hydrolysis (Saponification)
Triglycerides undergo hydrolysis in the presence of alkali, producing glycerol and
soap (salts of fatty acids).
Acid Hydrolysis
Hydrolysis in presence of HCl or H₂SO₄ forms free fatty acids and glycerol.
Hydrogenation
