Biochemistry · MU Pleven

27. Metabolism of Triacylglycerols. Regulation of Lipolysis and Lipogenesis in Various Organs. Glycerol Metabolism and Oxygenation. Role of Lipolysis in Thermogenesis

Covers how triacylglycerols are stored and broken down, from dietary digestion and chylomicron transport through hormone-driven lipolysis by hormone-sensitive lipase. It then takes glycerol handling, fatty acid synthesis, and the hormonal control of both processes, with separate notes on liver, adipose tissue and muscle. It ends with how lipolysis supplies fatty acids that activate UCP-1 in brown fat to produce heat.

Inside: 8 sections · 6 labelled pictures · 12 flashcards · 3 min

Topic 27 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 8 sections, about 444 words (3 min of reading), with 12 flashcards.

In this note

  1. Metabolism of Triacylglycerols.
  2. Metabolism of Triacylglycerols (TAGs)
  3. Lipolysis (Breakdown of TAGs)
  4. Glycerol Metabolism and Oxidation
  5. Lipogenesis (Synthesis of Fatty Acids and TAGs)
  6. Regulation of Lipolysis and Lipogenesis (Hormonal Control)
  7. Organ-Specific Regulation
  8. Role of Lipolysis in Thermogenesis

Metabolism of Triacylglycerols (TAGs)

  • Triacylglycerols (TAGs) are the major storage form of energy in the body, composed of three fatty acids esterified to glycerol.
  • Storage sites:
  • Mainly in adipose tissue, but also present in liver, muscle, and other tissues.
  • TAGs form lipid droplets coated by proteins like perilipin.
  • Dietary TAGs: Digestion:
  • Broken down in the intestine by pancreatic lipase and bile salts → free fatty acids + 2-monoacylglycerol.
  • Absorption and Transport:
  • Re-esterified in intestinal mucosa → packaged into chylomicrons → enter lymph → bloodstream.
  • Lipoprotein lipase (in capillaries of adipose and muscle) hydrolyzes TAGs in chylomicrons.
  • Storage in Adipose Tissue:
  • Insulin stimulates uptake of glucose.
  • Glucose → DHAP (dihydroxyacetone phosphate) → Glycerol-3-phosphate (substrate for TAG synthesis).
  • Free fatty acids + glycerol-3-phosphate → TAGs.

Lipolysis (Breakdown of TAGs)

  • Occurs mainly in adipocytes when energy is needed.
  • Stimulated by hormones: Epinephrine, norepinephrine, glucagon, cortisol.
  • Inhibited by insulin.
  • Key enzyme: Hormone-Sensitive Lipase (HSL).
  • Mechanism:
  • Hormone binds β-adrenergic receptor → activates adenylate cyclase → ↑ cAMP → activates PKA.
  • PKA phosphorylates HSL and perilipin, allowing lipase access to lipid droplet.
  • TAG → Free fatty acids (FFAs) + glycerol.
  • FFAs are released to the bloodstream bound to albumin, transported to tissues for β-oxidation.
  • Glycerol is transported to liver for metabolism.

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