Enzymes, biological molecules, metabolism, and the processes that supply cells with energy.
Textbooks report different ATP yields for aerobic glucose metabolism because the underlying biochemistry is not a single fixed number. The yield depends on how many protons each ATP synthase uses, which electron carriers shuttle electrons, and whether the calculation includes ATP spent on other cellular processes. Consequently, authors adopt different conventions, leading to the familiar 30‑38, 29‑32, or 24‑30 ATP ranges.
The electron transport chain (ETC) is a series of membrane‑embedded proteins that move electrons from NADH and FADH₂ to oxygen, using the released energy to pump protons and create a gradient that drives ATP synthesis. Oxygen is the final electron acceptor, forming water, and the whole process yields most of the ATP from glucose.
Cellular respiration converts glucose and oxygen into carbon dioxide, water, and usable energy (ATP). It proceeds through glycolysis, the pyruvate‑oxidation step, the Krebs cycle, and oxidative phosphorylation, yielding up to 30‑32 ATP per glucose molecule.
Enzymes are protein (or RNA) catalysts that speed up biochemical reactions by lowering the activation energy without being consumed. They achieve this through specific binding to substrates at an active site, stabilizing the transition state, and releasing products unchanged.