Biochemistry : Oxidative Phosphorylation Energetics

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Oxidative Phosphorylation Energetics

Below are standard reduction potentials of components in carbohydrate metabolism 

 

 

What is the free energy change for this reaction?

Possible Answers:

Correct answer:

Explanation:

First, let's consider the half reactions involved to determine 

This overall reaction involves the donation of 2 electrons, so

 is defined as . The reaction we drew earlier is shown below:

We can see that  was oxidized and  was reduced. Find .

 is Faraday's constant, and is defined as: 

Solve for 

 

Example Question #2 : Oxidative Phosphorylation Energetics

Which of the following processes involved in cellular respiration has a positive Gibbs Free energy?

Possible Answers:

The movement of the electrons through the electron transport chain

The combination of oxaloacetate and acetyl-CoA to form citrate in the Kreb's cycle

The movement of hydrogens through ATP synthase

The pumping of hydrogens from the mitochondrial matrix to the intermembrane space

The final step in glycolysis

Correct answer:

The pumping of hydrogens from the mitochondrial matrix to the intermembrane space

Explanation:

A positive Gibbs free energy implies that the process in question should be unfavorable under normal conditions.  The only process listed that is unfavorable and requires an input of energy is the pumping of hydrogen ions into the intermembrane space.  This occurs during the electron transport chain.

Example Question #3 : Oxidative Phosphorylation Energetics

In what phase of cellular respiration is not ATP produced?

Possible Answers:

Pyruvate dehydrogenase complex

Electron transport chain

Glycolysis

Krebs cycle

Every phase of cellular respiration produces some ATP

Correct answer:

Pyruvate dehydrogenase complex

Explanation:

The phases of cellular respiration are glycolysis, pyruvate dehydrogenase complex, Krebs cycle, electron transport chain. Glycolysis produces a net total of 2 ATP, the Krebs cycle produces 1 GTP that is converted to ATP in another process, and the electron transport chain is where almost all of the ATP made in cellular respiration is formed. However, during the pyruvate dehydrogenase complex phase of cellular respiration, pyruvate is converted to acetyl-CoA as a preparation for the Krebs cycle, but no ATP is created.

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