What is the total theoretical ATP yield from one glucose molecule during cellular respiration?

The total theoretical ATP yield from one glucose molecule during cellular respiration is most commonly considered to be 36 ATP molecules when taking into account the efficiencies of different processes involved. Cellular respiration consists of several stages: glycolysis, the citric acid cycle (Krebs cycle), and the electron transport chain.

During glycolysis, which occurs in the cytoplasm, two ATP molecules are produced directly, and an additional four ATP molecules are generated through substrate-level phosphorylation. However, two of those ATP molecules are used in the process, leading to a net yield of two ATP molecules.

In the citric acid cycle, which takes place in the mitochondria, each molecule of glucose yields two turns of the cycle (since one glucose results in two pyruvate molecules). Each turn produces one ATP directly and generates reducing equivalents in the form of NADH and FADH2 – these are vital for ATP production in the electron transport chain.

The electron transport chain, located in the mitochondrial inner membrane, produces the majority of ATP through oxidative phosphorylation, utilizing the NADH and FADH2 produced in earlier steps. For every NADH molecule, approximately 2.5 ATP can be generated, and for every FADH2, about 1.5 ATP