Mitochondria produce ATP during cellular respiration by converting the chemical energy stored in glucose (or other fuels) into a usable form of energy for the cell. This process is essentially the same in both animal and plant cells. The main difference is that plant cells also have chloroplasts, which make glucose through photosynthesis; mitochondria in plants then break down that glucose just as they do in animals.
The most important stage of ATP production is shown here:
Here's how the process works step by step:
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Glycolysis (in the cytoplasm)
- One glucose molecule is split into two molecules of pyruvate.
- A small amount of ATP is produced directly.
- High-energy electron carriers called NADH are also produced.
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Pyruvate oxidation and the citric acid (Krebs) cycle (in the mitochondrial matrix)
- Pyruvate enters the mitochondrion and is converted into acetyl-CoA.
- The Krebs cycle releases carbon dioxide (CO₂).
- More NADH and FADH₂ are produced, along with a small amount of ATP.
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Electron transport chain (inner mitochondrial membrane)
- NADH and FADH₂ donate high-energy electrons to a series of protein complexes.
- As electrons move through the chain, energy is released.
- This energy pumps hydrogen ions (H⁺) from the matrix into the space between the inner and outer mitochondrial membranes, creating a proton gradient.
- Oxygen acts as the final electron acceptor, combining with electrons and H⁺ to form water.
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ATP synthase and chemiosmosis
- The high concentration of H⁺ outside the matrix creates stored potential energy.
- H⁺ flows back into the matrix through the enzyme ATP synthase.
- The movement of H⁺ powers ATP synthase like a tiny molecular turbine.
- ATP synthase joins ADP and inorganic phosphate (Pi) to form ATP.
Why this works
The proton gradient functions like water behind a dam. Pumping H⁺ ions across the membrane stores energy, and when the ions flow back through ATP synthase, that stored energy is converted into chemical energy in ATP.
ATP yield
From one glucose molecule, a typical eukaryotic cell produces approximately:
- 2 ATP from glycolysis
- 2 ATP from the Krebs cycle
- About 26–28 ATP from oxidative phosphorylation (electron transport chain and ATP synthase)
This gives a total of roughly 30–32 ATP per glucose, although the exact number can vary depending on the cell type and how reducing equivalents are transported into mitochondria.
In both animal and plant cells, mitochondria are therefore the primary site of ATP production through cellular respiration. Plant cells simply have an additional organelle—the chloroplast—that produces the glucose that mitochondria can later use as fuel.
