Lipid Chemistry 1 MBBS B55.pdf

Introduction to Lipid Chemistry

  • Lipid constitutes a heterogeneous group of compounds of biochemical importance.

  • They are water insoluble (hydrophobic) but soluble in nonpolar solvents.

  • Deficiencies or imbalances of lipid metabolism can lead to significant clinical issues such as diabetes mellitus, where fatty acids and lipoprotein metabolism are deranged, leading to ketosis.

  • Steroid hormones play major roles in body homeostasis.

Learning Objectives

  1. Explain the functions of lipids

  2. Classify lipids with examples

  3. Show the schematic structure of triacylglycerol

  4. Show the schematic representation of the general structure of a phospholipid

  5. List the function of phospholipids:

    • Phosphatidic acid

    • Phosphatidylcholine

    • Phosphatidylinositol

    • Sphingomyelin

  6. List the classes of glycosphingolipids with examples

  7. Describe cerebrosides: occurrence, composition, function, and examples

  8. List classes of acidic glycosphingolipids (gangliosides and sulfatedia) with emphasis on cholera toxin receptor

  9. Name the plasma lipoproteins

  10. Classify fatty acids based on various criteria (nature, nutritional requirement, length, and number of carbon atoms) and interpret their representations.

Clinical Significance of Lipids

  • Obesity

  • Diabetes mellitus

  • Atherosclerosis

  • Fatty liver

  • Lipid storage diseases

  • Hyperlipoproteinemia

Functions of Lipids

  • Major storage form of energy.

  • Structural components of biomembranes (phospholipids and cholesterol).

  • Metabolic regulators (steroid hormones and prostaglandins).

  • Serve as surfactants, detergents, and emulsifying agents (amphipathic lipids).

  • Protect internal organs with pads of fat.

  • Aid in the absorption of fat-soluble vitamins.

  • Act as electric insulators in neurons.

  • Provide insulation against drastic temperature changes.

  • Assist in determining body shape and contour.

Classification of Lipids

  1. Simple Lipids

    • Esters of fatty acids with glycerol or other alcohols.

      • Types:

        • Fats: Fatty acids + glycerol (e.g., Triacylglycerol or Triglycerides)

        • Waxes: Fatty acid esters with other higher alcohols.

  2. Compound Lipids

    • Fatty acids esterified with alcohol and contain other groups (e.g., phospholipids, glycosphingolipids).

  3. Derived Lipids

    • Compounds derived from lipids or lipid precursors (e.g., steroids, fatty acids).

  4. Lipids Complexed to Other Compounds

    • Macromolecular complexes of lipids with proteins (e.g., lipoproteins).

Triacylglycerol (TAG)

  • Composed of three fatty acid chains and glycerol.

  • Represents the main storage form of energy.

  • Excess dietary fatty acids are converted into TAG and stored in adipocytes.

Phospholipids

  • Compound lipids containing a glycerol backbone with fatty acid chains and a phosphate group.

  • Predominantly found in cell membranes and important for cellular functions.

  • The phospholipid structure is amphipathic, featuring both hydrophobic and hydrophilic parts, which aids in forming bilayers.

Classes of Phospholipids

  1. Glycerophospholipids: Contain glycerol (main components in membranes).

  2. Sphingophospholipids (e.g., Sphingomyelin): Contain sphingosine, important in the myelin sheath of nerve fibers.

Functions of Phosphatidic Acid (PA)

  • Precursor for biosynthesis of various lipids.

  • Acts as a second messenger in cellular signaling.

  • Involved in membrane dynamics and influences membrane curvature.

Functions of Phosphatidylcholine (PC)

  • A key component of lung surfactant which reduces surface tension in alveoli, preventing collapse.

  • Important in cell signaling and as a component in various biological membranes.

Prostaglandins

  • Derived lipids synthesized from arachidonic acid, involved in inflammation and cell signaling.

  • NSAIDs inhibit COX enzymes to reduce prostaglandin production, lowering inflammation and pain.