Fatty acid oxidation is a crucial process in energy metabolism. It breaks down fatty acids into acetyl-CoA units, providing a significant source of energy for cells. This process involves transporting fatty acids into mitochondria and a series of chemical reactions known as .
The breakdown of fatty acids yields more energy per gram than carbohydrates or proteins. Understanding fatty acid oxidation is key to grasping how our bodies use stored fat for fuel, especially during fasting or extended physical activity.
Fatty Acid Transport and Activation
Carnitine Shuttle System
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Thiolase cleaves 3-ketoacyl-CoA, releasing acetyl-CoA and shortened acyl-CoA
Energy Yield and Regulation
Each cycle produces one FADH2, one NADH, and one acetyl-CoA
FADH2 and NADH feed into electron transport chain for ATP production
Acetyl-CoA enters citric acid cycle for further oxidation
Process regulated by availability of fatty acids and energy demand
Malonyl-CoA inhibits carnitine palmitoyltransferase I, controlling fatty acid entry into mitochondria
Hormone-sensitive lipase in adipose tissue regulates fatty acid release into bloodstream
Ketone Body Formation
Ketogenesis Process
Ketone bodies form when acetyl-CoA accumulates beyond capacity of citric acid cycle
Occurs during fasting, low-carbohydrate diets, or uncontrolled diabetes
Three main ketone bodies: acetoacetate, β-hydroxybutyrate, and acetone
Acetoacetate synthesized from two acetyl-CoA molecules
β-hydroxybutyrate formed by reduction of acetoacetate
Acetone produced by spontaneous decarboxylation of acetoacetate
Ketone Body Utilization and Metabolism
Ketone bodies serve as alternative fuel source for brain and other tissues
Brain can derive up to 70% of its energy from ketone bodies during prolonged fasting
Liver cannot use ketone bodies due to lack of necessary enzymes
Extrahepatic tissues convert ketone bodies back to acetyl-CoA for energy production
Excessive ketone body production leads to ketoacidosis, a potentially dangerous condition
regulates ketone body production by controlling fatty acid release from adipose tissue
Key Terms to Review (18)
Acyl-coa dehydrogenase: Acyl-CoA dehydrogenase is an enzyme that catalyzes the first step in the β-oxidation of fatty acids, where it converts acyl-CoA into trans-Δ²-enoyl-CoA by introducing a double bond between the α and β carbon atoms. This enzyme plays a crucial role in the metabolism of fatty acids, impacting energy production through the breakdown of long-chain fatty acids into acetyl-CoA units for energy generation. The activity of acyl-CoA dehydrogenase is essential for maintaining proper energy balance in cells, particularly during periods of fasting or prolonged exercise.
ATP: ATP, or adenosine triphosphate, is the primary energy currency of the cell, providing the energy needed for various biochemical reactions. It plays a critical role in metabolic processes, serving as a link between energy-releasing pathways and energy-consuming activities within the cell.
Beta-oxidation: Beta-oxidation is the metabolic process by which fatty acids are broken down in the mitochondria to generate acetyl-CoA, which can then enter the citric acid cycle for energy production. This process involves the sequential removal of two-carbon units from the fatty acid chain, leading to the production of reducing equivalents in the form of NADH and FADH2, which are essential for ATP generation through oxidative phosphorylation.
Cardiomyopathy: Cardiomyopathy is a disease of the heart muscle that affects its size, shape, and ability to pump blood effectively. This condition can lead to heart failure and other serious complications, as the heart becomes weaker and less efficient at circulating blood throughout the body. Understanding cardiomyopathy is crucial since it can arise from various causes, including genetic factors, long-term high blood pressure, or damage from previous heart attacks.
Enoyl-coa hydratase: Enoyl-CoA hydratase is an enzyme that catalyzes the hydration of enoyl-CoA intermediates during the β-oxidation of fatty acids. This reaction converts an enoyl-CoA into a 3-hydroxyacyl-CoA by adding a water molecule, facilitating the breakdown of fatty acids for energy production. The role of this enzyme is crucial in enabling cells to efficiently utilize fatty acids, especially during periods of fasting or increased energy demand.
Fatty acyl-CoA: Fatty acyl-CoA is a fatty acid molecule that has been activated by the addition of coenzyme A (CoA), making it a key intermediate in various metabolic pathways, particularly in fatty acid oxidation. This activation is essential because it allows fatty acids to be transported into the mitochondria and utilized for energy production through β-oxidation, where they are broken down to generate ATP. The formation of fatty acyl-CoA from fatty acids is a crucial step for energy metabolism in cells.
Glucagon: Glucagon is a peptide hormone produced by the alpha cells of the pancreas that plays a crucial role in glucose metabolism by raising blood glucose levels when they fall too low. It stimulates various metabolic pathways, ensuring that the body has enough energy, especially during fasting or low-carbohydrate intake.
Insulin: Insulin is a peptide hormone produced by the pancreas that plays a crucial role in regulating glucose levels in the blood. It facilitates the uptake of glucose into cells, promotes glycogen synthesis, and inhibits gluconeogenesis, thereby maintaining energy homeostasis in the body.
Ketosis: Ketosis is a metabolic state characterized by elevated levels of ketone bodies in the blood, which occurs when the body shifts from using glucose as its primary energy source to utilizing fat. This process is typically induced by a low-carbohydrate diet, fasting, or prolonged exercise, leading to increased fat oxidation and the production of ketones as an alternative fuel source. Ketosis is crucial for energy balance, especially during periods of low carbohydrate availability.
Medium-chain acyl-coa dehydrogenase deficiency: Medium-chain acyl-CoA dehydrogenase deficiency is a genetic metabolic disorder that affects the body's ability to break down medium-chain fatty acids, leading to the accumulation of these fats in the body. This condition is linked to the fatty acid oxidation process, which is crucial for producing energy from fats, and can cause serious health problems, especially during periods of fasting or illness.
Mitochondrial fatty acid oxidation: Mitochondrial fatty acid oxidation is the metabolic process by which fatty acids are broken down in the mitochondria to produce energy in the form of ATP. This process involves several key steps, including the activation of fatty acids, their transport into the mitochondria, and their subsequent degradation through beta-oxidation, which generates acetyl-CoA and reducing equivalents for the electron transport chain.
NADH: NADH, or Nicotinamide Adenine Dinucleotide (Reduced form), is a crucial coenzyme found in all living cells that plays a key role in cellular respiration and energy production. It acts as an electron carrier, facilitating the transfer of electrons in metabolic processes, particularly during glycolysis and the citric acid cycle, ultimately contributing to ATP synthesis via oxidative phosphorylation.
Oxidative phosphorylation: Oxidative phosphorylation is the process by which ATP is produced in cells through the electron transport chain and the chemiosmotic coupling of protons across a membrane. This process is crucial for cellular energy production, linking the breakdown of nutrients to ATP synthesis, and is tightly regulated to meet cellular energy demands.
Peroxisomal fatty acid oxidation: Peroxisomal fatty acid oxidation is a metabolic process occurring in peroxisomes, where very long-chain fatty acids are broken down into shorter-chain fatty acids for energy production. This process plays a crucial role in lipid metabolism and is distinct from mitochondrial fatty acid oxidation, as it primarily handles fatty acids that are longer than 20 carbon atoms. The end products of peroxisomal oxidation are shorter fatty acids, which can then be transported to the mitochondria for further processing.
Refsum Disease: Refsum disease is a rare genetic disorder that affects the metabolism of phytanic acid, resulting from a deficiency in the enzyme phytanoyl-CoA hydroxylase. This condition leads to the accumulation of phytanic acid in various tissues, which can cause neurological and cardiac symptoms. The disease is directly linked to disruptions in fatty acid oxidation, particularly in the breakdown of branched-chain fatty acids.
Saturated Fatty Acids: Saturated fatty acids are a type of fat molecule characterized by having no double bonds between carbon atoms, meaning all carbon atoms are fully saturated with hydrogen atoms. This structural feature contributes to their solid state at room temperature and their impact on human health, particularly in relation to cardiovascular diseases and cholesterol levels.
Trans-fatty acids: Trans-fatty acids are a type of unsaturated fatty acid that are formed when hydrogen is added to liquid vegetable oils to make them more solid, a process known as hydrogenation. These fatty acids are commonly found in partially hydrogenated oils and have been associated with various health issues, particularly in the context of fatty acid oxidation and metabolism.
Unsaturated Fatty Acids: Unsaturated fatty acids are fatty acids that contain one or more double bonds in their hydrocarbon chain, leading to fewer hydrogen atoms compared to saturated fatty acids. This structural feature results in a bend or kink in the chain, affecting the physical properties of the fats and oils they compose, such as their fluidity and melting points. Unsaturated fatty acids play crucial roles in various biological processes, including energy storage and membrane fluidity.