During the electron transport chain, reactive oxygen species, specifically superoxide radicals (O2-), are generated from quinones and released into the mitochondrial matrix. These superoxide radicals are subsequently converted into hydrogen peroxide (H2O2) by the enzyme superoxide dismutase. This process is crucial as hydrogen peroxide is further reduced to water by glutathione peroxidase, which utilizes glutathione in its reaction. The oxidation of glutathione requires NADPH, highlighting one of the key roles of NADPH in cellular metabolism, particularly in the pentose phosphate pathway.
To understand the overall standard redox potential of electron transport, we start with NADH, which initiates the process. The reaction can be represented as:
\[ \text{NADH} \rightarrow \text{NAD}^+ + \text{H}^+ + 2 \text{e}^- \]
This reaction has a standard reduction potential of +0.32 volts. The overall redox potential is calculated by summing the oxidation potential and the reduction potential. Given two reduction potentials, we reverse one to represent oxidation, leading to:
\[ 0.32 \, \text{V} + 0.82 \, \text{V} = 1.14 \, \text{V} \]
Next, to determine the energy released when one mole of electrons moves between cytochrome a3 and a1 in complex IV, we apply the Gibbs free energy equation:
\[ \Delta G = -nFE \]
Here, ΔG represents the change in Gibbs free energy, n is the number of moles of electrons transferred, and F is Faraday's constant (approximately 96,500 J/V·mol). The electrons transition from a1 to a3, necessitating the reversal of the oxidation potential. The relevant reduction potentials are 0.35 V for a3 and 0.29 V for a1, leading to:
\[ E = 0.35 \, \text{V} - 0.29 \, \text{V} = 0.06 \, \text{V} \]
Substituting into the Gibbs free energy equation with n = 1, we find:
\[ \Delta G = -1 \times 96,500 \, \text{J/V·mol} \times 0.06 \, \text{V} = -5,790 \, \text{J/mol} \, \text{or} \, -5.79 \, \text{kJ/mol} \]
This calculation illustrates the energy dynamics involved in electron transport and the importance of redox potentials in cellular respiration. The subsequent discussion on photophosphorylation will further explore these energy transfer processes in photosynthesis.
