Lipid Biochemistry

Jul 16, 2024

Lipid Biochemistry - Key Points

Introduction

  • Focus: Free fatty acids (central to lipid biochemistry).
  • Important Backbones:
    • Glycerol backbones
    • Sphingosine backbones
  • Two essential organic chemistry mechanisms.

Organic Chemistry Mechanisms

Mechanism 1: Hydroxyl and Carboxyl

  • Steps:
    1. Deprotonation of hydrogen
    2. Formation of oxygen anion (nucleophilic)
    3. Attack on carbon (electrophilic)
    4. Formation of tetrahedral intermediate
    5. Bond formation and breakdown (electrons on oxygen)
  • Product: Ester

Mechanism 2: Hydroxyl and Phosphoester

  • Steps:
    1. Deprotonation of hydrogen
    2. Formation of oxygen anion (nucleophilic)
    3. Attack on phosphate (electrophilic)
    4. Formation of trigonal bipyramidal intermediate
    5. Bond formation and breakdown (electrons on oxygen)
  • Product: Phosphodiester

Glycerol Backbone

Formation

  • Derived from glycolysis intermediates.
  • Can be formed by attaching three fatty acids.

Triglycerides

  • Step-by-Step Formation:
    1. Addition of one fatty acid - Monoglyceride
    2. Addition of second fatty acid - Diglyceride
    3. Addition of third fatty acid - Triglyceride
  • Function: Primary stored form of energy.

Phospholipids

  • Formation: Two fatty acids + one phosphate
  • Structure: Phospholipid makes up plasma membranes.
  • Addition of various other groups (e.g., choline, ethanolamine) through hydroxyl group.

Glycolipids

  • Formation:
    1. Hydroxyl group converted to a leaving group
    2. Nucleophilic attack on carbon
    3. Formation of glycosidic linkage
  • Types:
    • Cerebrosides (single carbohydrate)
    • Gangliosides (multiple carbohydrates)

Sphingosine Backbone

Formation

  • Reaction between a fatty acid and serine amino acid.
  • Product: Ceramide

Importance of Ceramide

  • Can form various complex lipids by adding different head groups.

Examples

  • Sphingomyelins: Phospho head group, important for myelin sheath.
  • Cerebrosides: Single carbohydrate.
  • Gangliosides: Multiple carbohydrates, including sialic acid.

Cholesterol and Complex Lipids

Biosynthesis Pathway

  • Start: Acetyl-CoA
  • Intermediate: HMG-CoA
  • Building Blocks: Five-carbon units
  • Chain: 10-carbon → 15-carbon → 30-carbon (squalene)

Importance of Cholesterol

  • Forms essential molecules like bile salts, vitamin D, testosterone, estradiol, cortisol, and aldosterone.
  • Can be synthesized from glucose via glycolysis and HMG-CoA pathway.

Roles of Cholesterol

  • Liver: Bile salts for fat digestion
  • Kidney: Conversion to vitamin D
  • Endocrine System: Production of sex hormones and adrenal hormones