Energy is conserved and transferred in cellular respiration through a series of chemical reactions where the energy stored in glucose is gradually released and used to generate ATP (adenosine triphosphate), the cell's primary energy currency.
Here's a breakdown:
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Initial Energy Source: Cellular respiration begins with glucose (a sugar molecule) as the primary source of energy.
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Gradual Energy Release: Instead of releasing all the energy at once (which would be damaging to the cell), cellular respiration breaks down glucose in a controlled, step-by-step manner. This occurs through a series of metabolic pathways: glycolysis, the Krebs cycle (also known as the citric acid cycle), and the electron transport chain.
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Electron Carriers: During glycolysis and the Krebs cycle, high-energy electrons are removed from glucose and transferred to electron carriers like NAD+ and FAD, forming NADH and FADH2, respectively. These molecules act like "energy shuttles."
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Electron Transport Chain (ETC): NADH and FADH2 deliver their high-energy electrons to the electron transport chain, located in the inner mitochondrial membrane. As electrons move through the ETC, they release energy.
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ATP Synthesis: The energy released by the electron transport chain is used to pump protons (H+) across the inner mitochondrial membrane, creating a proton gradient. This gradient drives ATP synthase, an enzyme that uses the flow of protons back across the membrane to convert ADP (adenosine diphosphate) into ATP. This process is called oxidative phosphorylation.
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ATP: The Energy Currency: ATP stores the energy in its chemical bonds. When a cell needs energy to perform work (e.g., muscle contraction, protein synthesis), ATP is broken down (hydrolyzed) into ADP and inorganic phosphate, releasing the stored energy.
Summary Table:
| Process | Location | Input | Output | Key Energy Transfer |
|---|---|---|---|---|
| Glycolysis | Cytoplasm | Glucose | Pyruvate, ATP, NADH | Glucose energy partially transferred to ATP and NADH |
| Krebs Cycle | Mitochondrial Matrix | Pyruvate (converted to Acetyl CoA) | CO2, ATP, NADH, FADH2 | Acetyl CoA energy transferred to ATP, NADH, and FADH2 |
| Electron Transport Chain | Inner Mitochondrial Membrane | NADH, FADH2, O2 | H2O, ATP | NADH/FADH2 energy used to create proton gradient for ATP production |
In essence, the energy in glucose is progressively transferred through a series of redox reactions (oxidation and reduction) to ATP, making it available for cellular work.
