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 7.3, the pH of the matrix has been measured as 7.6. (a)  Calculate [H+] in the external medium and in the matrix under these conditions. (b)  What is the outside-to-inside ratio of [H+]? Comment on the energy inherent in this concentration difference (just the energy from the concentration gradient, not the electrochemical potential). Assume this a mammalian system, so the temperature is constant at 37oC). (c)  Calculate the number of free protons in a respiring liver mitochondrion, assuming its inner matrix compartment is a sphere of diameter 1.6 microns.  (volume of a sphere is 4/3 pi r3 )

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
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  1. 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 7.3, the pH of the matrix has been measured as 7.6.

(a)  Calculate [H+] in the external medium and in the matrix under these conditions.

(b)  What is the outside-to-inside ratio of [H+]? Comment on the energy inherent in this concentration

difference (just the energy from the concentration gradient, not the electrochemical potential). Assume this a mammalian system, so the temperature is constant at 37oC).

(c)  Calculate the number of free protons in a respiring liver mitochondrion, assuming its inner matrix compartment is a sphere of diameter 1.6 microns.  (volume of a sphere is 4/3 pi r3 )

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