Metabolism of Triglycerides and Fats

Introduction to Lipid Metabolism

• Fats are stored as triglycerides in adipose and liver tissue.
• Scientific term for fats is lipids.
• Triglycerides can also be referred to as triacylglycerol (TAG).

Structure of Triacylglycerol

• Composed of a glycerol head and fatty acid tails.

Lipid Metabolism Pathways

Lipolysis

• Occurs during fasting state when energy is needed after carbohydrate stores are depleted.
• Triglycerides are broken down into glycerol and fatty acids.
• This process of breaking down is called lipolysis.

Lipogenesis

• Occurs in the fed state, when insulin is high.
• Involves converting fatty acids and glycerol back into triglycerides.
• This synthesis process is known as lipogenesis.

Glycerol Metabolism

• Glycerol is a 3-carbon molecule.
• Converted into Dihydroxyacetone Phosphate (DHAP).
• DHAP can be used in glycolysis, forming glycolytic intermediates and eventually ATP.

Fatty Acid Metabolism

• Fatty acids are broken down via beta-oxidation into Acetyl CoA.
• Acetyl CoA enters the Krebs cycle, producing NADH, FADH2, and ATP.

Excess Glucose and Fatty Acid Synthesis

• Excess glucose can lead to conversion of Acetyl CoA into fatty acids.
• Glycerol synthesis from DHAP is a precursor for triglyceride synthesis.

Fatty Acid Synthesis

• Acetyl CoA can be used to synthesize fatty acids.
• These fatty acids combine with glycerol to form triglycerides.

Glycerol Synthesis

• Conversion of DHAP to glycerol, which is essential for triglyceride formation.

Ketogenesis

• In conditions like starvation or uncontrolled diabetes, excess Acetyl CoA leads to production of ketone bodies.
• Ketone bodies (Acetoacetate and Beta-Hydroxybutyrate) are alternative energy sources for the brain and muscles.
• Formation of ketone bodies from Acetyl CoA is called ketogenesis.

Ketolysis

• Ketone bodies are broken down back into Acetyl CoA for energy in brain and muscle tissues.
• This process is called ketolysis.

Cholesterol Synthesis

• Acetyl CoA is a precursor for cholesterol synthesis.
• Cholesterol is vital for:
  • Bile salts production for fat digestion.
  • Steroid hormones synthesis.
  • Cell membrane structure.

Summary of Key Processes

• Lipolysis: Breakdown of triglycerides into glycerol and fatty acids.
• Lipogenesis: Formation of triglycerides from glycerol and fatty acids.
• Beta-oxidation: Conversion of fatty acids into Acetyl CoA.
• Ketogenesis: Formation of ketone bodies from Acetyl CoA.
• Ketolysis: Breakdown of ketone bodies back to Acetyl CoA.
• Cholesterol synthesis: Production of cholesterol from Acetyl CoA.

Next Steps

• In the upcoming video, the focus will be on how proteins and amino acids integrate into the metabolic pathway and a discussion on gluconeogenesis.