Multiple Choice
How many molecules of ATP are gained by substrate-level phosphorylation from the complete breakdown of a single molecule of glucose in the presence of oxygen?
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8. Respiration
Types of Phosphorylation
4:51 minutesProblem 5
Textbook Question
Compare and contrast substrate-level phosphorylation and oxidative phosphorylation.
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Step 1: Understand the terms: Substrate-level phosphorylation and oxidative phosphorylation are two different ways cells generate ATP. ATP, or adenosine triphosphate, is the main energy currency of the cell.
Step 2: Define substrate-level phosphorylation: Substrate-level phosphorylation is a type of ATP synthesis that occurs when an enzyme directly transfers a phosphate group from a substrate molecule to ADP, creating ATP. This process occurs in the cytoplasm during glycolysis and in the mitochondrion during the Krebs cycle.
Step 3: Define oxidative phosphorylation: Oxidative phosphorylation is a process that uses energy released by the electron transport chain to power ATP synthesis. It occurs in the mitochondria during cellular respiration. Here, electrons are transferred from electron donors to electron acceptors such as oxygen, in redox reactions. These reactions release energy, which is used to form ATP.
Step 4: Compare and contrast: Both processes generate ATP but in different ways and at different stages of cellular respiration. Substrate-level phosphorylation directly transfers a phosphate group to ADP to form ATP, while oxidative phosphorylation uses energy from the electron transport chain to add a phosphate group to ADP. Substrate-level phosphorylation occurs during glycolysis and the Krebs cycle, while oxidative phosphorylation occurs during the electron transport chain.
Step 5: Summarize: In summary, substrate-level phosphorylation and oxidative phosphorylation are both crucial for ATP synthesis, but they differ in their mechanisms and stages of occurrence during cellular respiration.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Substrate-Level Phosphorylation
Substrate-level phosphorylation is a metabolic process that directly generates ATP by transferring a phosphate group from a substrate molecule to ADP. This occurs in specific enzymatic reactions, primarily during glycolysis and the citric acid cycle. Unlike oxidative phosphorylation, it does not involve the electron transport chain and is less efficient in terms of ATP yield.
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Oxidative Phosphorylation
Oxidative phosphorylation is a process that produces ATP through the electron transport chain and chemiosmosis, occurring in the mitochondria. Electrons from NADH and FADH2 are transferred through a series of proteins, creating a proton gradient that drives ATP synthesis via ATP synthase. This method is more efficient than substrate-level phosphorylation, yielding significantly more ATP per glucose molecule.
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ATP Yield Comparison
The comparison of ATP yield between substrate-level and oxidative phosphorylation highlights their efficiency differences. Substrate-level phosphorylation typically produces 2 ATP molecules per glucose during glycolysis and the citric acid cycle, while oxidative phosphorylation can yield approximately 28-34 ATP molecules per glucose, depending on the efficiency of the electron transport chain. Understanding this difference is crucial for grasping cellular energy production.
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