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The Electron Transport Chain

4. Electron transport translocates protons from the mitochondrialmatrix 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 7.4, the pH of the matrix has been measured as 7.7.
a. Calculate [H+] in the external medium and in the matrix under these conditions.
b. What is the outside: inside ratio of [H+] ? Is there energy inherent in this concentration? Explain.
c. Calculate the number of protons in a respiring liver mitochondrian, assuming its inner matrix compartment is a sphere of diameter of 1.5 micro meter.

5. Calculate:
a. The protonmotive force across the inner mitochondrial membrane at 25 degree celsius when the elcetrical difference is -0.18 V (inside negative), the pH outside is 6.7, and the pH inside is 7.5.
b. The percentage of energy from the chemical (pH) gradient and the percentage from the charge gradient.
c. The total free energy available for the phosphorylation of ADP.

6. In the presence of saturating amounts of oxaloacetate,the activity of citrate synthase from pig heart tissue shown a sigmoid dependence on the concentration of acetyl-CoA. When succinyl- CoA is added, the curve shifts to the right and the sigmoid dependence is more produced.
a. On that basis of those observations, suggest how succinyl- CoA regulates the activity of citrate synthase.
b. Why is succinyl - CoA an appropriate signal for the regulation of the citric acid cycle?
c. How does the regulation of citrate synthase control the rate of cellular respiration in pig heart tissue?
4. Electron transport translocates protons from the mitochondrialmatrix 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 7.4, the pH of the matrix has been measured as 7.7.
a. Calculate [H+] in the external medium and in the matrix under these conditions.
b. What is the outside: inside ratio of [H+] ? Is there energy inherent in this concentration? Explain.
c. Calculate the number of protons in a respiring liver mitochondrian, assuming its inner matrix compartment is a sphere of diameter of 1.5 micro meter.

5. Calculate:
a. The protonmotive force across the inner mitochondrial membrane at 25 degree celsius when the elcetrical difference is -0.18 V (inside negative), the pH outside is 6.7, and the pH inside is 7.5.
b. The percentage of energy from the chemical (pH) gradient and the percentage from the charge gradient.
c. The total free energy available for the phosphorylation of ADP.

6. In the presence of saturating amounts of oxaloacetate,the activity of citrate synthase from pig heart tissue shown a sigmoid dependence on the concentration of acetyl-CoA. When succinyl- CoA is added, the curve shifts to the right and the sigmoid dependence is more produced.
a. On that basis of those observations, suggest how succinyl- CoA regulates the activity of citrate synthase.
b. Why is succinyl - CoA an appropriate signal for the regulation of the citric acid cycle?
c. How does the regulation of citrate synthase control the rate of cellular respiration in pig heart tissue?

Solution Preview

4. Electron transport 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 7.4, the pH of the matrix has been measured as 7.7.

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

pH = - log [H+]

Therefore, for the medium, 7.4 = - log [H+]

[H+] = antilog -7.4

[H+] = 4.0x10^-8 M

And, for the matrix, you do the same thing. Work it out. You should get:

[H+] = 2.0x10^-8 M

b. What is the outside: inside ratio of [H+] ? Is there energy inherent in this concentration? Explain.

Therefore, the outside:inside ratio is simply:

4.0x10^-8 / 2.0x10^-8 = 2

Concentration gradients have free energy inherent in them. Why? Because, a concentration gradient will always tend towards equilibrium. That will be a spontaneous process. For spontaneous processes, deltaG is negative, indicating a release of free energy.

c. Calculate the number of protons in a respiring liver mitochondrian, assuming its inner matrix compartment is a sphere of diameter of 1.5 micrometer.

First, we need to calculate the volume of the sphere. You can look up the mathematical equation describing the volume of a sphere in any mathematics textbook.

V = 4/3 x (pi ...

Solution Summary

The solution provides detailed calculations and explanations for various questions regarding the electron transport chain.

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