Cellular respiration

Cellular respiration is the set of cellular reactions that releases energy from organic molecules and captures much of it in ATP, chiefly through oxidation and electron transfer.

Glycolysis: A sequence of reactions that splits glucose into pyruvate, producing ATP and NADH. It begins glucose breakdown and yields a small amount of ATP before oxygen-dependent stages.
Glucose: A six-carbon monosaccharide that serves as a major fuel molecule in cells. Its oxidation supplies carbon and electrons to several stages of respiration.
Fermentation: An anaerobic pathway that regenerates NAD+ by transferring electrons to organic molecules without an electron transport chain. It sustains glycolysis when oxidative phosphorylation cannot proceed, but yields much less ATP per glucose.
Photosynthesis: A set of reactions that converts light energy into chemical energy and, in oxygenic organisms, releases oxygen. It stores energy in organic molecules, whereas respiration releases energy from them.
Pyruvate oxidation: The conversion of pyruvate into acetyl-CoA, carbon dioxide, and NADH. It connects glycolysis to the citric acid cycle while transferring electrons to NAD+.
Adenosine triphosphate: A nucleotide that transfers chemical energy through its phosphate groups to drive cellular processes. It is the principal energy product captured by cellular respiration.
Aerobic respiration: Cellular respiration that uses oxygen as the final electron acceptor in the electron transport chain. It enables extensive oxidation of fuel and high ATP yield in oxygen-using cells.
Oxidative phosphorylation: ATP production driven by electron transport and a proton gradient across a membrane. It is the ATP-generating stage of respiration, not the entire respiratory process.
Citric acid cycle: A cyclic pathway that oxidizes acetyl-CoA to carbon dioxide and generates reduced electron carriers. It extracts additional electrons from carbon fuel for delivery to the respiratory chain.
Nicotinamide adenine dinucleotide: A coenzyme that carries electrons between metabolic reactions in oxidized NAD+ and reduced NADH forms. Respiratory pathways load NADH with electrons that feed the electron transport chain.

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