GLOSSARY

Coupled Reaction is a reaction mechanistically linked to another process.

Gibbs free energy describes thermodynamic favorability under specified conditions, not reaction speed by itself. Exergonic and endergonic concern free-energy change; exothermic and endothermic concern heat, so the pairs are not interchangeable. Concentrations and conditions alter actual values. Standard-condition numbers cannot simply be transferred unchanged to every cell or interpreted as the entire energy content of a meal. Thermodynamic direction and physiological rate answer different questions.

Cells couple energy-requiring processes to favorable ones through actual mechanisms such as group transfer or conformational change, not merely adjacent arrows. ATP synthesis and use are important links. Energy is transformed rather than created from nothing: food fuel supports work, heat and stored structures. Coupling concerns the combined reaction, so a single unfavorable step can proceed within a favorable network without violating thermodynamics or supplying free dietary energy.

Activation energy is the reaction barrier, distinct from final free-energy change. Enzymes alter kinetics through catalysis without automatically shifting thermodynamic equilibrium. More enzyme does not necessarily raise flux without substrate and suitable regulation. Supplement claims must separate a named enzyme's biological role from demonstrated effects of ingestion in humans. Catalytic capacity, substrate delivery and the net pathway outcome are linked but not identical quantities or guaranteed performance benefits.