Biochemical Processes of Lipids and Functionality

Small Intestine and Lipid Functions

  • Receptors and Enzymes
    • Enzymes or channels change cell biochemistry.
    • Affect lipid composition in liver cell membranes.
    • Insulin regulates glucose import by promoting fusion of vesicles containing glucose transporters with the membrane.

Signal Transduction Mechanisms

  • Insulin Role in Lipid Modification
    • Insulin triggers phosphorylation of phosphatidylinositol.
    • Phosphate groups added at positions 3 and 4 of phosphatidylinositol.

Types of Lipids

  • Categories of Lipids:
    • Fatty Acids
    • Building blocks for lipids.
    • Identified by the number of carbons and double bonds.
    • Triglycerides
    • Consist of three fatty acids linked to glycerol via ester bond.
    • Main function: energy storage and insulation.
    • Phospholipids
    • Composed of fatty acids, glycerol, phosphate groups, and other molecules like choline.
    • Sterols
    • Include cholesterol, crucial for membrane structure and hormone synthesis.

Fatty Acid Structure

  • Composition:
    • Carbon chain with a carboxylic acid at one end.
    • Structure affects properties: saturation leads to flexibility (kinks) that affects melting point.
  • Importance of Double Bonds:
    • More double bonds decrease melting point referring to unsaturated fats.
    • Example: Arachidonic acid, a 20:4 (n-6) fatty acid, has multiple double bonds that impact its function.

Triglycerides

  • Energy Storage:
    • Efficient storage form (less weight compared to glycogen).
    • Humans store about 30 lbs of triglycerides, enough for 2-3 months of energy.
    • Can be sourced from dietary intake or synthesized from carbohydrates.

Glycerol and Phospholipid Formation

  • Phospholipid Formation:
    • Built around glycerol with fatty acids linked through ester bonds.
    • Building blocks include fatty acids and hydroxyl-containing molecules (e.g., glycerol, serine).
    • Phosphatidic acid as a key example of phospholipid structure.

Signal Transduction via Lipids

  • Phosphoinositides play crucial roles in cell signaling, affecting various biochemical pathways.
  • Hydrolysis of phospholipids generates signaling molecules like diacylglycerol and inositol phosphate which mobilize calcium from endoplasmic reticulum.

Sphingolipids vs. Glycerophospholipids

  • Sphingolipids:
    • Built around sphingosine with a fatty acid attached via an amide bond.
    • Include ceramide (fatty acid + sphingosine) and sphingomyelin (ceramide + phosphate group).
    • Important in cell membranes and signaling processes.

Steroids and Cholesterol

  • Structure:
    • Composed of four fused carbon rings, forming the steroid nucleus.
    • Example: Cholesterol, a precursor for other steroids and important for membrane integrity.
  • Role in Health:
    • High levels of LDL (bad cholesterol) are associated with arterial blockage; HDL (good cholesterol) helps remove LDL from circulation.

Role of Hormones Derived from Steroids

  • Cortisol:
    • Involved in stress response, regulates glucose production, and suppresses immune function.
  • Aldosterone:
    • Regulates blood pressure through water retention in kidneys.