Krebs / citric acid cycle | Cellular respiration | Biology | Khan Academy
Khan Academy・13 minutes read
Glycolysis and the Krebs cycle convert glucose into ATP and other energy carriers, yielding a total of 38 ATPs through cellular respiration, which includes the electron transport chain. Acetyl-CoA plays a crucial role in this process, allowing for the catabolism of carbohydrates, proteins, and fats, showcasing the body's energy production versatility.
Insights
- Glycolysis initiates the breakdown of glucose by converting it into two 3-carbon pyruvate molecules, resulting in a net gain of 2 ATPs and 2 NADHs, and this process occurs in the cytoplasm without the need for oxygen, making it adaptable to both aerobic and anaerobic environments.
- The Krebs cycle, which follows glycolysis, processes acetyl-CoA to produce carbon dioxide, ATP, NADH, and FADH2, ultimately contributing to the electron transport chain, where the combined yield from one glucose molecule can reach a theoretical maximum of 38 ATPs, showcasing the efficiency of cellular respiration in energy production.
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Recent questions
What is cellular respiration?
Cellular respiration is a biochemical process that converts glucose and other organic molecules into energy in the form of adenosine triphosphate (ATP). It involves several stages, including glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis occurs in the cytoplasm and breaks down glucose into pyruvate, yielding a small amount of ATP and NADH. The Krebs cycle, which takes place in the mitochondrial matrix, further processes pyruvate into carbon dioxide while generating more NADH, FADH2, and ATP. Finally, the electron transport chain utilizes the NADH and FADH2 produced to create a significant amount of ATP through oxidative phosphorylation. The entire process is essential for providing energy to cells and can occur under both aerobic and anaerobic conditions.
How do enzymes function in metabolism?
Enzymes play a crucial role in metabolism by acting as biological catalysts that speed up chemical reactions within the body. Each enzyme is specific to a particular reaction or type of reaction, lowering the activation energy required for the reaction to proceed. In the context of cellular respiration, enzymes facilitate each step of the metabolic pathways, such as glycolysis and the Krebs cycle, ensuring that glucose is efficiently converted into ATP. By binding to substrates and stabilizing the transition state, enzymes increase the rate of reactions, allowing cells to meet their energy demands effectively. Without enzymes, metabolic processes would occur too slowly to sustain life.
What is the role of acetyl-CoA?
Acetyl-CoA is a vital metabolic intermediate that plays a key role in cellular respiration. It is produced from the breakdown of carbohydrates, fats, and proteins, making it a central hub for energy production. Once formed, acetyl-CoA enters the Krebs cycle, where it combines with oxaloacetic acid to form citric acid, initiating a series of reactions that lead to the production of ATP, NADH, and FADH2. This versatility allows the body to utilize various fuel sources for energy, highlighting the importance of acetyl-CoA in metabolism. Its ability to link different metabolic pathways underscores its significance in maintaining energy homeostasis in the body.
What is the Krebs cycle?
The Krebs cycle, also known as the citric acid cycle, is a series of enzymatic reactions that occur in the mitochondrial matrix, playing a critical role in cellular respiration. It begins with the combination of acetyl-CoA and oxaloacetic acid to form citric acid, which undergoes a series of transformations. Throughout the cycle, citric acid is oxidized, leading to the release of carbon dioxide and the production of high-energy molecules, including NADH, FADH2, and ATP. For each turn of the cycle, significant amounts of energy are harvested, which are essential for the subsequent electron transport chain. The Krebs cycle is fundamental for energy production and is a key component of aerobic metabolism.
How is ATP produced in cells?
ATP, or adenosine triphosphate, is produced in cells through a series of metabolic processes, primarily during cellular respiration. The process begins with glycolysis, where glucose is broken down into pyruvate, yielding a small amount of ATP. Following glycolysis, the Krebs cycle further processes pyruvate, generating additional ATP along with NADH and FADH2. The majority of ATP is produced during the electron transport chain, where the high-energy electrons from NADH and FADH2 are transferred through a series of proteins, ultimately leading to the synthesis of ATP via oxidative phosphorylation. This efficient production of ATP is crucial for powering various cellular functions and maintaining overall energy balance in the body.
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Summary
00:00
Cellular Respiration and ATP Production Explained
- Glycolysis begins with a glucose molecule, a 6-carbon structure, which is split into two 3-carbon pyruvate molecules, resulting in a net gain of 2 ATPs and 2 NADHs after using 2 ATPs and producing 4 ATPs.
- The glycolysis process occurs in the cytoplasm of the cell and does not require oxygen, allowing it to function in both aerobic and anaerobic conditions.
- Following glycolysis, pyruvate oxidation occurs, where each pyruvate loses one carbon atom, resulting in the formation of a 2-carbon compound called acetyl-CoA, along with the reduction of NAD+ to NADH.
- The Krebs cycle, also known as the citric acid cycle, takes place in the mitochondrial matrix and begins with the combination of acetyl-CoA (2 carbons) and oxaloacetic acid (4 carbons) to form citric acid (6 carbons).
- During the Krebs cycle, citric acid undergoes a series of reactions where two carbon atoms are cleaved off, producing carbon dioxide (CO2) and generating NADH, FADH2, and ATP in the process.
- For each glucose molecule, the Krebs cycle produces 6 CO2 (3 per pyruvate), 6 NADHs (3 per pyruvate), 2 ATPs (1 per pyruvate), and 2 FADH2s (1 per pyruvate).
- The total yield from glycolysis and the Krebs cycle for one glucose molecule is 4 ATPs, 10 NADHs, and 2 FADH2s, which are crucial for the next stage of cellular respiration.
- In the electron transport chain, each NADH can produce approximately 3 ATPs, leading to a total of 30 ATPs from the 10 NADHs, while each FADH2 produces about 2 ATPs, contributing an additional 4 ATPs from the 2 FADH2s.
- The overall theoretical maximum yield of ATP from one glucose molecule through cellular respiration is 38 ATPs, accounting for the ATP produced in glycolysis, the Krebs cycle, and the electron transport chain.
- The entire process of cellular respiration is enzyme-catalyzed, with enzymes facilitating each step, ensuring the efficient conversion of glucose into usable energy in the form of ATP.
13:27
Energy Production in Cellular Respiration Explained
- The electron transport chain, following glycolysis and the Krebs cycle, contributes to the production of a total of 38 ATP in a highly efficient cell, with 34 ATP generated from the electron transport chain and 4 ATP from glycolysis and the Krebs cycle combined. This theoretical maximum is important for AP biology and introductory courses.
- Carbohydrate metabolism, specifically sugar catabolism, is the primary focus, starting with glucose. However, the body can also catabolize proteins and fats for energy, with fats being convertible to glucose in the liver, allowing them to enter cellular respiration.
- Acetyl-CoA serves as a key catabolic intermediary that can enter the Krebs cycle, regardless of whether the fuel source is carbohydrates, proteins, or fats, highlighting the versatility of energy production in the body.
- In the Krebs cycle, each pyruvate produces four NADH, one ATP, and one FADH2, with the process involving the oxidation of citric acid and the reduction of NAD+ to NADH, as well as the formation of guanosine triphosphate (GTP), which can later be converted to ATP.
