Lipid Metabolism: Fatty Acid Oxidation for Energy Production

Lipid Metabolism

• Fatty acid oxidation occurs in mitochondria and is a major consumer of fat in muscle.
• Fatty acids are more calorific than glucose, yielding approximately 38 kJ/mol compared to 16 kJ/mol for glucose.

Fatty Acid Oxidation

• Fatty acid oxidation provides quantitatively more ATP than glucose oxidation, but the rate of ATP generation is slower.
• Insulin inhibits hormone-sensitive lipase (HSL) via dephosphorylation, while glucagon activates HSL via phosphorylation.
• In the fed state, insulin is dominant, while in the fasted state, glucagon is dominant.

β-Oxidation

• β-oxidation is the catabolic process by which FA molecules are broken down in the mitochondria to generate acetyl-CoA.
• Acetyl-CoA enters the TCA cycle and produces NADH and FADH2, which are coenzymes used in the electron transport chain.
• β-oxidation is named as such because the β carbon of the FA undergoes oxidation to a second carbon (carbonyl carbon).

α-Oxidation

• Branched-chain, 20 carbon fatty acid, phytanic acid, undergoes α-oxidation because of the methyl group on its β carbon.
• Refsum disease is a rare, autosomal recessive disorder caused by the accumulation of phytanic acid in the plasma and tissues.

Ketone Bodies

• Ketone bodies are important sources of energy for peripheral tissues.
• Ketone bodies are produced in the liver during prolonged fasting and are used in proportion to their concentration in the blood.
• Even the brain can use ketone bodies to help meet its energy needs if the blood levels rise sufficiently.

Ketone Bodies in Diabetes Mellitus

• Excessive production of ketone bodies in diabetes mellitus can lead to diabetic ketoacidosis.
• A frequent symptom of diabetic ketoacidosis is a fruity odor on the breath, which results from increased production of acetone.
• Ketoacidosis can cause severe acidosis due to the increased number of H+ circulating in a decreased volume of plasma.

Learn about the role of fatty acids in muscle energy production, comparing their energy yield with glucose, and understanding fatty acid oxidation in mitochondria.