Cellular Respiration and Energy Flow
ATP and Metabolism
Energy transfer in cells
ATP couples energy-releasing reactions to energy-requiring ones. Metabolic pathways are organized into sequences of enzyme-catalyzed steps, allowing efficient control and regulation.
Aerobic respiration
Aerobic respiration includes glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation. Most ATP is produced when electrons from NADH and FADH drive the electron transport chain and chemiosmosis.
Mechanistic insight
The proton gradient across the inner mitochondrial membrane stores potential energy that is converted into ATP by ATP synthase.
Major stages of respiration
| Stage | Main outcome |
|---|---|
| Glycolysis | Glucose is split into pyruvate with a small ATP yield |
| Citric acid cycle | Carbon is oxidized and reduced coenzymes are produced |
| Electron transport chain | Electrons drive proton pumping |
| Chemiosmosis | Proton flow powers ATP synthesis |
Which process directly produces most ATP in aerobic respiration?
Oxidative phosphorylation, including chemiosmosis, is the major ATP-producing stage.
Correct answer: Oxidative phosphorylation
Why can fermentation help cells survive without oxygen?
Without oxygen, the electron transport chain stops; fermentation restores NAD+ balance.
Correct answer: It regenerates NAD+ so glycolysis can continue.
What is the role of oxygen in aerobic respiration?
Oxygen accepts electrons at the end of the electron transport chain, allowing continued electron flow.
Correct answer: It acts as the final electron acceptor