Concept explainers
To review:
The standard free energy change for the reaction
Introduction:
The phosphoryl group transfer potential of a compound can be defined as the measure of the strength of attachment of a group to the molecule. It refers to the differences in the standard free energy of the molecule with and without the group. NADH has a higher phosphoryl group transfer potential than FADH2 (flavin adenine dinucleotide).
Explanation of Solution
The reduction of oxygen to water by FADH2can be depicted as follows:
For calculating the standard free energy, thenumber of electrons transferred needs to be balanced. For a reaction, the standard free energy can be calculated by using the Nernst equation, which is as follows:
Where,
n is the number of electrons transferred,
F is Faraday’s constant, which is 96.15 kJ/V.mol (kilojoule per Volt. mole), and
∆E°’ is the overall cell potential.
∆E°’ is the overall cell potential.
∆E°’ can be calculated using the following formula:
In the given case, E°’ of electron acceptor is +0.82 V and that of electron donor is -0.22 V.
Putting the values of n, F, and ∆E°’ in the Nernst equation:
Thus, the standard free energy of the reaction is –199.992 kJ/mol.
The reduction of oxygen to water by NADH can be depicted as follows:
For calculating the standard free energy, the number of electrons transferred needs to be balanced. For a reaction, the standard free energy can be calculated by using the Nernst equation.
Thus,
The value of standard reduction potential (Eº’) for electron acceptor in this case is 0.82 V and for electron donor is –0.32 V. Therefore,
Putting the values of n, F, and ∆E°’ in the Nernst equation:
Thus, the standard free energy of the reaction is -219.222 kJ/mol.
Thus, it can be concluded that the standard free energy of reduction of oxygen to water by FADH2 is -199.992 kJ/mo, lnd the standard free energy of reduction of oxygen to water by NADH is -219.222 kJ/mol.
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