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Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Question

Given the following information on reduction potentials, calculate the standard free energy in kJ/mol based on your understanding of electron transfer through the pyruvate dehydrogenase complex. Round to nearest whole number.

Lipoamide + 2H+ + 2e- → dihydrolipoamide ∆ε^ο = -0.29

FAD + 2H+ + 2e- → FADH₂ ∆ε^ο= −0.01

Expert Solution

Initial calculations

The 2 half reactions of the reaction of interest is given in question. The reaction of interest that takes place in pyruvate dehydrogenase complex is the transfer of 2 electrons and 2 H⁺ from dihydrolipoamide to FAD and the reaction is given below.

Dihydrolipoamide + FAD $\to$ Lipoamide + FADH₂

First we need to find change in standard reduction potential value ( $∆ E^{' 0}$ ) of the above reaction.

$∆ E^{' 0} = {E^{' 0}}_{(o f e l e c t r o n a c c e p t o r)} - {E^{' 0}}_{(o f e l e c t r o n d o n o r)}$

Here the electron acceptor is FAD whose E^'0 value is given as -0.01 V and the electron donor is Dihydrolipoamide whose E^'0 is given as -0.29 V . E^'0 is the standard reduction potential value of reduction half reaction of species; it is represented as $∆ ε^{0}$ in question.

$∆ E^{' 0} = {E^{' 0}}_{o f e l e c t r o n a c c e p t o r} - {E^{' 0}}_{o f e l e c t r o n d o n o r} = - 0.01 V - (- 0.29 V) = 0.28 V$