Question Video: Applying Knowledge of Hydrogen Ions to the Electron Transport Chain Biology

Assume oxidative phosphorylation is happening continuously in mitochondria. If the number of hydrogen ions in the intermembrane space significantly increases, what effect will this have?

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Video Transcript

Assume oxidative phosphorylation is happening continuously in mitochondria. If the number of hydrogen ions in the intermembrane space significantly increases, what effect will this have? (A) Fewer molecules of carbon dioxide will be released. (B) More reduced NAD and FAD will be produced. (C) More ATP will be produced. Or (D) less ATP will be produced.

Oxidative phosphorylation takes place in the inner mitochondrial membrane of eukaryotic cells. Within the inner mitochondrial membrane are a collection of proteins, enzymes, proton pumps, and electron carriers that make up the electron transport chain. Let’s have a closer look at the electron transport chain to help us answer this question.

Here, we have a simplified version of the electron transport chain, showing just two proton pumps and the enzyme ATP synthase. The inner mitochondrial membrane, where the electron transport chain is found, separates the mitochondrial matrix from the intermembrane space. The primary role of the proton pumps is to actively transport hydrogen, H+, ions from the matrix and into the intermembrane space. These hydrogen ions accumulate in relatively high concentrations in the intermembrane space. They then move down their concentration gradient through the channel of ATP synthase. ATP synthase couples this movement of hydrogen ions to the phosphorylation of ADP, which produces ATP.

Let’s look back to our question. Using what we now know about oxidative phosphorylation, what will happen if the number of hydrogen ions in the intermembrane space significantly increases? If there are more hydrogen ions in the intermembrane space, this means there are more hydrogen ions available to move through the channel of ATP synthase. This in turn means that there will be an increase in the number of ADP molecules being phosphorylated. Therefore, more ATP will be produced.

Looking back to our answers, we can see that our only correct choice is option (C). If the number of hydrogen ions in the intermembrane space significantly increases, more ATP will be produced.

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