Notes on Lipids

Introduction to Lipids

  • Lipids are naturally occurring compounds.
    • Soluble in organic solvents (hydrocarbons, chloroform, benzene, ethers, and alcohols).
    • Water-insoluble organic molecules.
  • Not classified as polymers unlike proteins, nucleic acids, and polysaccharides.
  • Small molecules with a tendency to associate via noncovalent forces.

Interactions of Lipids

  • Types of noncovalent interactions in lipids:
    • Ionic bonds (example: NaCl).
    • Hydrogen bonds (especially with N, O, F).
    • Van der Waals forces.
    • Hydrophobic interactions (involves nonpolar molecules).

Functions of Lipids

  • Energy Storage:
    • Serve as a primary energy reserve, especially triglycerides.
  • Cushioning:
    • Protect organs against mechanical shock.
  • Insulation:
    • Provide thermal insulation.
  • Absorption:
    • Aid in the absorption of fat-soluble vitamins.
  • Signaling:
    • Participate in lipid signaling.

Types of Lipids

  • Fatty Acids:

    • Monocarboxylic acids with hydrocarbon chains.
    • Important for energy and metabolic fuels.
    • Yield more energy upon oxidation (37 kJ/g) than carbohydrates or protein (16 kJ/g).

  • Triacylglycerols:

    • Composed of glycerol with three fatty acids.
    • Can be simple (e.g., tristearin) or mixed triglycerides.

  • Waxes:

    • Fatty acids esterified to long-chain alcohols.
    • Functions include waterproofing and structural roles.

  • Phospholipids:

    • Major components of biological membranes.
    • Amphipathic molecules (both hydrophobic and hydrophilic parts).

Fatty Acids

  • Saturated Fatty Acids:
    • Examples: Palmitic acid (16:0), Stearic acid (18:0).
  • Monoenoic Fatty Acids:
    • Example: Oleic acid (18:1).
  • Polyunsaturated Fatty Acids:
    • Example: Linoleic (18:2) and Arachidonic acid (20:4).
  • Linoleic acid is essential and can’t be synthesized by the body.

Triacylglycerols

  • Serve as the primary energy storage form.
  • Usually consist of three different fatty acids attached to glycerol.
  • Store more energy than carbohydrates due to their density and energy yield.

Complex Lipids

  • Phospholipids:
    • Key components of membranes, including phosphatidylcholine, phosphatidylethanolamine.
  • Sphingolipids:
    • Important in membranes and for signaling; includes sphingomyelin, cerebrosides.

Eicosanoids

  • Derivatives of arachidonic acid, act as local signaling molecules (e.g., Prostaglandins, Thromboxanes).
  • Have roles in inflammation and physiological responses.

Cholesterol and Steroids

  • Cholesterol is an essential component of membranes and a precursor for steroid hormones.
    • Examples of steroid hormones: glucocorticoids, aldosterone, sex hormones.

Lipoproteins

  • Complexes of lipids and proteins that transport lipids in the bloodstream.
  • Types include: Chylomicrons, VLDL, LDL, HDL, etc.
    • Chylomicrons: Largest, transport dietary lipids.
    • LDL: Delivers cholesterol to cells; known as 'bad cholesterol'.

Health Implications

  • Familial Hypercholesterolemia:
    • Genetic condition leading to high cholesterol and risk of cardiovascular diseases.
  • Eicosanoid Role in Inflammation:
    • Aspirin inhibits eicosanoid synthesis, impacting pain and inflammation processes.