Viesta 3 PDF - Cellular Respiration - Anaplerosis

In anaerobic conditions, the net yield of ATP from one glucose molecule is 2 ATP. This occurs through the process of glycolysis, which is the breakdown of glucose into pyruvate. While glycolysis produces 4 ATP molecules, 2 are used up in the process, leaving a net gain of 2 ATP. It's important to...

In anaerobic conditions, the net yield of ATP from one glucose molecule is 2 ATP. This occurs through the process of glycolysis, which is the breakdown of glucose into pyruvate. While glycolysis produces 4 ATP molecules, 2 are used up in the process, leaving a net gain of 2 ATP. It's important to note that anaerobic respiration is less efficient than aerobic respiration, which can produce up to 38 ATP molecules per glucose molecule. However, anaerobic respiration is essential for organisms that cannot access oxygen or in situations where oxygen is limited. - The net yield of ATP from the oxidation of one glucose molecule is 38 ATP molecules. This occurs through a series of processes, including glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis: Breaks down glucose into pyruvate, producing 2 ATP molecules. Krebs cycle: Further breaks down pyruvate, producing 2 ATP molecules, 6 NADH molecules, and 2 FADH2 molecules. Electron transport chain: Uses NADH and FADH2 to generate ATP through oxidative phosphorylation, producing 34 ATP molecules. Therefore, the total net yield is 2 + 2 + 34 = 38 ATP molecules. - Anaplerosis: Replenishing the Krebs Cycle Anaplerosis is a biochemical process that involves the replenishment of intermediates in the Krebs cycle (also known as the citric acid cycle). This cycle is vital for cellular respiration, providing energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. Why is Anaplerosis Necessary? Intermediate Depletion: The Krebs cycle intermediates are constantly being used for various cellular processes, such as amino acid synthesis, fatty acid synthesis, and heme synthesis. Without replenishment, these intermediates would become depleted, hindering the cycle's function. Metabolic Flexibility: Anaplerosis allows organisms to adapt to changing metabolic conditions. For example, when there is a shortage of carbohydrates, anaplerotic reactions can convert amino acids or fatty acids into Krebs cycle intermediates, ensuring a continuous supply of energy. Common Anaplerotic Reactions: 1. Pyruvate Carboxylation: This reaction converts pyruvate into oxaloacetate, a key Krebs cycle intermediate. It is catalyzed by the enzyme pyruvate carboxylase and requires biotin as a cofactor. 2. Amino Acid Transamination: Amino acids can be converted into Krebs cycle intermediates through transamination reactions. For example, glutamate can be converted into alpha-ketoglutarate, and aspartate can be converted into oxaloacetate. 3. Propionyl-CoA Carboxylation: Propionyl-CoA, a product of fatty acid metabolism, can be converted into succinyl-CoA, a Krebs cycle intermediate. This reaction is catalyzed by propionyl-CoA carboxylase and requires biotin. Significance of Anaplerosis: Energy Production: Anaplerosis ensures a steady supply of Krebs cycle intermediates, which are essential for generating ATP through oxidative phosphorylation. Metabolic Regulation: It plays a crucial role in metabolic regulation, allowing organisms to adapt to different nutritional and environmental conditions. Amino Acid and Fatty Acid Synthesis: Anaplerotic reactions provide intermediates for the synthesis of amino acids and fatty acids, which are essential building blocks of cells and tissues. In summary, anaplerosis is a vital process that maintains the integrity of the Krebs cycle and supports various metabolic functions. By replenishing depleted intermediates, anaplerosis contributes to the overall energy metabolism of cells. - The steps in the TCA cycle (also known as the citric acid cycle) where carbon dioxide is liberated during the oxidation of glucose are: 1. Isocitrate to α-ketoglutarate: This step involves the oxidative decarboxylation of isocitrate, catalyzed by the enzyme isocitrate dehydrogenase. In this reaction, one molecule of carbon dioxide is released. 2. α-ketoglutarate to succinyl-CoA: This step also involves oxidative decarboxylation, catalyzed by α-ketoglutarate dehydrogenase complex. Another molecule of carbon dioxide is released in this reaction. Therefore, during the oxidation of one glucose molecule, a total of two molecules of carbon dioxide are liberated in the TCA cycle. These carbon dioxide molecules are ultimately exhaled as waste products.