Homework+6+Solutions

Homework+6+Solutions - BME 221 Homework #6 Due: Beginning...

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BME 221 Homework #6 Due: Beginning of class on December 11 th 1. A series of reactions that take place in the inner membrane of mitochondria consist of transferring electrons from NADH to several intermediate molecules and ultimately to oxygen to form water (and to generate a proton gradient across the inner membrane of mitochondria). The first electron transfer reaction in this process is the one between NADH and Coenzyme Q. The two electrochemical half-reactions are, along with their biological standard half- potentials: Coenzyme Q + 2 H + + 2 e - Coenzyme QH 2 ; E° = + 0.04 V NAD + + H + + 2 e - NADH ; E° = - 0.32 V Imagine you would be able to use these two reactions to make a battery (ignore possible technical difficulties). a) Which half reaction would be constitute the minus pole, and which the plus pole? The minus pole is the site of oxidation, so NAD + + H + + 2 e - NADH. The plus pole is the site of reduction, so Coenzyme Q + 2 H + + 2 e - Coenzyme QH 2. b) Write the half reactions in the direction in which they would occur in such a battery (i.e. reactants on the left side of the reaction equation and products on the right side of the reaction equation). Coenzyme Q + 2 H + + 2 e - Coenzyme QH 2 NADH NAD + + H + + 2 e - c) What would be the standard potential difference of such a battery? E° = E° pp - E° mp E° = 0.04V – (-0.32V) = 0.36V d) Would this potential difference i) go up , ii) stay constant, or iii) go down, if the concentration of NADH would be higher than 1.00 mol/L (circle one)? E = E° - RT/vF * lnQ NADH is a reactant. Adding more reactant above its standard concentration of 1.00M would cause Q to decrease and E to increase. 2. If the mitochondrial electric potential between the intermembrane space and the matrix were 70mV (with the more negative potential in the matrix), as is common for other membranes, how many moles of ATP could be synthesized from the movement of 4 moles H + from the intermembrane space to the matrix, assuming the pH of the matrix is 1.4 pH units higher than in the intermembrane space? Also assume biological standard conditions and a temperature of 25°C. Δµ H+ = FΔψ – (RT ln10) ΔpH Δµ H+ = (96500 C mol -1 ) x (0.07 V) - (8.3145 J mol -1 K -1 ) x (298 K) x (ln10) x (-1.4) Δµ H+ = +14.74 kJ mol -1 The energy required for phosphorylation of ADP to ATP under biological standard conditions is
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31 kJ mol -1 . The Gibbs energy available for phosphorylation from the transport of 4 mol H + is: ΔG = (+14.74 kJ mol
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Homework+6+Solutions - BME 221 Homework #6 Due: Beginning...

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