Lipids

1. Importance of Lipids

• Energy storage (high caloric value)
• The structural component of cell membranes
• Insulation and protection
• Precursor for hormones (steroids, prostaglandins)
• Role in signaling and metabolism

2. Classification of Lipids

A. Simple Lipids

• Fats & Oils (Triglycerides) – Esters of fatty acids with glycerol
• Waxes – Esters of fatty acids with long-chain alcohols

B. Complex Lipids

• Phospholipids – Contain phosphate group (e.g., phosphatidylcholine)
• Glycolipids – Contain sugar residues (e.g., cerebrosides, gangliosides)

C. Derived Lipids

• Steroids (cholesterol)
• Fatty acids
• Fat-soluble vitamins (A, D, E, K)

3. Structure & Properties of Fatty Acids

• Structure: Long hydrocarbon chains with a carboxyl (-COOH) group
• Saturation:
  • Saturated Fatty Acids (SFA) – No double bonds (e.g., palmitic acid)
  • Unsaturated Fatty Acids (UFA) – One or more double bonds (e.g., oleic acid)
• Essential Fatty Acids: Cannot be synthesized (e.g., linoleic & α-linolenic acid)
• Properties:
  • Longer chains → Higher melting point
  • More double bonds → Lower melting point, more fluidity

4. Storage Lipids

• Triacylglycerols (Triglycerides)
  • Three fatty acids + Glycerol backbone
  • Primary energy reserve in animals
  • Stored in adipose tissue
  • Insoluble in water

5. Membrane Lipids

• Phospholipids
  • Glycerophospholipids (e.g., lecithin)
  • Sphingophospholipids (e.g., sphingomyelin)
• Glycolipids (Carbohydrate + Lipid, e.g., cerebrosides)
• Cholesterol
  • Provides rigidity to membranes
  • Precursor for steroids