Fatty Acid Synthesis and Beta Oxidation

Fatty Acid Synthesis

• Occurs in the cytosol of adipose tissue and liver
• Key enzyme: fatty acid synthase (FAS)
• Acetyl-CoA is the primary building block
• Fatty acid synthesis is inhibited by:
  • High levels of ATP, NADH, and acetyl-CoA
  • Insulin
• Activated by:
  • Insulin
  • Citrate (activates acetyl-CoA carboxylase)
  • High glucose levels

Beta Oxidation

• Occurs in the mitochondria
• Breakdown of fatty acids into acetyl-CoA
• Four main steps:
  1. Activation of fatty acids into acyl-CoA
  2. Transport of acyl-CoA into the mitochondria
  3. Beta oxidation (repative cycle of 4 reactions)
  4. Electron transport chain and ATP synthesis
• Inhibited by:
  • Malonyl-CoA (product of fatty acid synthesis)
  • ATP and NADH
• Activated by:
  • Low glucose levels
  • High glucagon levels
  • Epinephrine

Triglyceride Metabolism

• Triglycerides (TG) are formed by esterifying glycerol with three fatty acids
• TG are stored in adipose tissue and released into the bloodstream as free fatty acids (FFA) and glycerol
• Hormone-sensitive lipase (HSL) is the key enzyme in TG breakdown
• TG metabolism is regulated by:
  • Insulin (inhibits TG breakdown, promotes synthesis)
  • Glucagon and epinephrine (activate TG breakdown)
• Lipoprotein lipase (LPL) breaks down TG in chylomicrons and VLDL in the bloodstream

Cholesterol Regulation

• Cholesterol is synthesized from acetyl-CoA in the liver
• Key enzyme: HMG-CoA reductase
• Cholesterol regulation is critical for maintaining proper membrane fluidity and function
• Regulation of cholesterol synthesis:
  • Inhibited by:
    • High cholesterol levels
    • Insulin
  • Activated by:
    • Low cholesterol levels
    • Thyroid hormone
    • SREBP (sterol regulatory element-binding protein)
• LDL receptors regulate cholesterol uptake in the liver and peripheral tissues

Fatty Acid Synthesis

• Takes place in the cytosol of adipose tissue and liver
• Fatty acid synthase (FAS) is the key enzyme
• Acetyl-CoA serves as the primary building block
• Inhibited by high levels of ATP, NADH, and acetyl-CoA, as well as insulin
• Activated by insulin, citrate, and high glucose levels

Beta Oxidation

• Occurs in the mitochondria
• Breaks down fatty acids into acetyl-CoA
• Consists of four main steps: activation of fatty acids, transport of acyl-CoA, beta oxidation, and electron transport chain and ATP synthesis
• Inhibited by malonyl-CoA, ATP, and NADH
• Activated by low glucose levels, high glucagon levels, and epinephrine

Triglyceride Metabolism

• Triglycerides are formed by esterifying glycerol with three fatty acids
• Stored in adipose tissue and released into the bloodstream as free fatty acids and glycerol
• Hormone-sensitive lipase (HSL) is the key enzyme in triglyceride breakdown
• Regulated by insulin, which inhibits triglyceride breakdown and promotes synthesis
• Glucagon and epinephrine activate triglyceride breakdown
• Lipoprotein lipase (LPL) breaks down triglycerides in chylomicrons and VLDL in the bloodstream

Cholesterol Regulation

• Synthesized from acetyl-CoA in the liver
• Key enzyme: HMG-CoA reductase
• Regulation is critical for maintaining proper membrane fluidity and function
• Inhibited by high cholesterol levels and insulin
• Activated by low cholesterol levels, thyroid hormone, and SREBP (sterol regulatory element-binding protein)
• LDL receptors regulate cholesterol uptake in the liver and peripheral tissues