Question

11. (13 pts) Electron transfer Electron transfer translocates protons from the mitochondrial matrix to the external medium, establishing a pH gradient across the inner membrane (outside more acidic than inside). The tendency of protons to diffuse back into the matrix is the driving force for ATP synthesis by ATP synthase. During oxidative phosphorylation by a suspension of mitochondria in a medium of pH 6.9, the pH of the matrix has been measured as 7.7. The temperature is 37 °C. A. (2 pts) Calculate (H') in the external medium and in the matrix under these conditions. B. (2 pts) What is the outside-to-inside ratio of [H*]? Comment on the energy inherent in this concentration difference.

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Answer 1

2 A. - log 10 (4+) = Pu; inverse - (H* J = 10-24 ſmit) in external medium = 10-7-44:0X 10-8M 147) in matrix = 10-7.7 = 2.0X10-8M 2 a B. The outside-to-inside ratio is 2:1, The free energy inherent in this concentration difference can be - calculated across inner membrane at a temperature of 25c. K = (C2/C1) = 2 mo Aco = - RT Ink Aco= A'GE-RIIN KIT T = Imlime imo OG'Or - RT In (3101) = -2476 fn( 2 ) =-17165 mol-1 51-72 KS MOI1 200 The energy available from tt concentation gradient ; 234pH RT = 9.3(0-3)(2476) = 1.7 KJ mol-1

to E. Synthesis of ATP arises from the proton gradient. All of the following from mitochondria except pentos phosphate pathway of 3 3 Election transport chain come to halt when ATP synthesis is blocked because it is necessary for oxidative phosphorylation of ADP to ATP.