Overview of Lipids

• Lipids are diverse macromolecules (fats, oils, hormones) that are hydrophobic and insoluble in water.
• Essential in diet: high energy value and source of fat-soluble vitamins.
• Present in all living organisms, forming membranes and energy storage.

Properties of Lipids

• Physical state: Can be liquid or solid at room temperature; colorless, odorless, tasteless.
• Chemical properties: Insoluble in water; soluble in organic solvents; no ionic charges.
• Saturated vs. Unsaturated: Solid triglycerides (saturated) vs. liquid triglycerides (unsaturated).

Lipid Hydrolysis and Reactions

1. Triglycerol Hydrolysis: Forms carboxylic acids and alcohols (hydrolysis process).
2. Saponification: Alkaline hydrolysis that produces soap.
3. Hydrogenation: Unsaturated fatty acids converted to saturated.
4. Halogenation: Unsaturated fatty acids react with halogens.
5. Rancidity: Unpleasant odors due to hydrolysis and oxidation.

Structure of Lipids

• Composed of Carbon, Hydrogen, and Oxygen; lower water content than carbohydrates.
• Made from glycerol and fatty acids (saturated or unsaturated).

Classes of Lipids

1. Simple Lipids: Fats and oils (yield fatty acids + glycerol); waxes (yield fatty acids + long-chain alcohols).
2. Compound Lipids: Phospholipids (yield fatty acids + glycerol + phosphoric acid) and glycolipids.
3. Derived Lipids: Hydrolysis products from other lipids (fatty acids, glycerol).

Triglycerides

• Main constituents of body fat, composed of three fatty acids esterified to glycerol.
• Functions: Energy storage, insulation, absorption of fat-soluble vitamins.

Fatty Acids

• Long-chain carboxylic acids with 4-36 carbon atoms; can be saturated (no C=C bonds) or unsaturated (C=C bonds exist).
• Saturated fatty acids: Unbranched, solid at room temperature. General formula: $CnH_{2n+1}COOH$.
• Unsaturated fatty acids: Contain C=C bonds, liquid at room temperature.

Glycerol

• Forms the backbone of triglycerides; reacts with fatty acids to form ester bonds via condensation (esterification).

Phospholipids

• Key component of cell membranes; consists of fatty acids, glycerol, and a phosphate group.
• Amphipathic nature: Hydrophilic heads and hydrophobic tails organize into bilayers.

Sterols (Cholesterol)

• Type of lipid with steroid structure; essential for cell membrane and precursor for hormones and vitamins.
• Regulates membrane fluidity; excess can lead to health issues (e.g., coronary artery disease).

Functions of Lipids

• Serve as energy reserves, insulation, and structural components of membranes.
• Act as enzyme activators and cofactors; play roles in cellular signaling and transduction.