Please answer question b You have previously calculated the free energy change o

ID: 268994 • Letter: P

Question

Please answer question b

You have previously calculated the free energy change of complex I as 53.06 kJ/mol and complex II as 33.58 kJ/mol. a) Calculate the free energy changes for complex III and complex IV from the overall reactions below. Be sure to show all work, including any half reactions and formula used. (10 points) Complex III CoQ (red.) +cytochrome c (oxid.)cytochrome c (red.)+ CoQ (oxid.) Complex IV: CoQ (oxid.)+21202CoQ (red.)+ H20 b) Electron transport does not directly generate any ATP. How does the electron transport chain generate energy for ATP synthesis and approximately how much free energy is put into this? Show your calculation for full credit. (8 points)

Explanation / Answer

Free energy Vs Reduction Potential

The redox reaction is sum of oxidation and reduction, in each half of reaction and each has an electrical potential. This is written as:

erxn= eoxidation + ereduction

Reduction Potentials

NAD+ + 2H+ + 2e- --> NADH + H+ -0.32 V

(1/2) O2 + 2H+ + 2e- --> H2O-+0.82 V

While electrical potential is converted into free energy (DG) i.e. usable energy by following equation:

DG= -nFerxn Joules

where n = number of electrons transferred (in moles, from the balanced equation), = Faraday constant (96,485 Coulombs/mole).

Hence the overall reaction for the oxidation of NADH paired with the reduction of O2 has a negative change in free energy (DG =-220 kJ); i.e., it is spontaneous. Thus, the higher the electrical potential of a reduction half reaction, the greater the tendency for the species to accept an electron.

Therefore, the calculation of energy during ETC can be written as follows

Complex Name

Half Reaction

Reduction Potential

Cyto. reductase

(also known as Cyto. b-c1 complex)

Cyto. b (Fe(III) center)
+ e- -->
Cyto. b (Fe(II) center)

-0.34 V
(at pH 7, T=30oC)

Cyto. c1 (Fe(III) center)
+ e- -->
Cyto. c1 (Fe(II) center)

+0.220 V
(at pH 7, T=30oC)

Cyto. c

Cyto. c (Fe(III) center)
+ e- -->
Cyto. c (Fe(II) center)

+0.250 V
(at pH 7, T=30oC)

Cyto. oxidase

Cyto. oxidase
( Fe(III) center) + e- -->
Cyto. oxidase
(Fe(II) center)

+0.285 V
(at pH 7.4, T=25oC)