Cytochrome, a complicated molecule that we will represent as CyFe2+, reacts with the air we breathe to supply energy required to synthesize adenosine triphosphate (ATP). The body uses ATP as an energy source to drive other reactions (Section 19.7). At pH 7.0 the following reduction potentials pertain to this oxidation of CyFe2+: O21g2 + 4 H+1aq2 + 4 e- ¡ 2 H2O1l2 Ered ° = +0.8 (b) If the synthesis of 1.00 mol of ATP from adenosine diphosphate (ADP) requires a ∆G of 37.7 kJ, how many moles of ATP are synthesized per mole of O2?

Key Concepts

Reduction Potentials

Reduction potentials indicate the tendency of a chemical species to acquire electrons and be reduced. A higher reduction potential means a greater likelihood of reduction occurring. In the context of cytochrome and oxygen, the given reduction potential helps determine the feasibility of the electron transfer process that ultimately contributes to ATP synthesis.

Gibbs Free Energy (∆G)

Gibbs Free Energy (∆G) is a thermodynamic quantity that represents the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. In biochemical reactions, a negative ∆G indicates that a reaction can occur spontaneously. The synthesis of ATP from ADP is coupled with the energy released from the oxidation of cytochrome, making it essential to understand how ∆G relates to the energy yield of the reaction.

Stoichiometry of Reactions

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. In this context, it is crucial to determine how many moles of ATP can be synthesized per mole of O2 consumed. By using the stoichiometric relationships derived from the reduction potentials and Gibbs Free Energy, one can quantify the efficiency of energy conversion in biological systems.