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What are the steps in cellular respiration?

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Cellular respiration can be broken down into several key stages, which occur in different parts of the cell. Here are the major steps:

  1. Glycolysis:

    • Occurs in the cytoplasm.
    • One molecule of glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (a three-carbon compound).
    • This process produces a net gain of 2 ATP molecules and 2 NADH molecules (electron carriers).

  2. Pyruvate Oxidation:

    • Takes place in the mitochondria (in eukaryotic cells).
    • Each pyruvate is converted into acetyl-CoA, releasing carbon dioxide and producing one NADH molecule per pyruvate. Since two pyruvate molecules are produced from one glucose, two NADH are generated in this step.

  3. Citric Acid Cycle (Krebs Cycle):

    • Also occurs in the mitochondrial matrix.
    • Each acetyl-CoA enters the cycle, combining with oxaloacetate to form citric acid.
    • The cycle goes through a series of reactions that release two molecules of carbon dioxide, produce one ATP (or GTP), and generate electron carriers: three NADH and one FADH₂ per turn (each glucose results in two turns of the cycle).

  4. Electron Transport Chain (ETC):

    • Located in the inner mitochondrial membrane.
    • The NADH and FADH₂ generated in the previous steps donate their electrons to the electron transport chain.
    • As electrons move through a series of protein complexes, their energy is used to pump protons (H⁺ ions) into the intermembrane space, creating a proton gradient.

  5. Chemiosmosis:

    • Protons flow back into the mitochondrial matrix through ATP synthase, a protein that harnesses the proton motive force to synthesize ATP from ADP and inorganic phosphate (Pi).
    • This process can produce approximately 26 to 28 ATP molecules, depending on the efficiency of the system.

  6. Oxidative Phosphorylation:

    • The overall process of using the energy from electrons (from NADH and FADH₂) to produce ATP via the electron transport chain and chemiosmosis.
    • The final electron acceptor in the chain is oxygen, which combines with electrons and protons to form water.

Overall, cellular respiration can yield up to 36 to 38 ATP molecules from a single molecule of glucose, depending on the specific conditions and cell type.