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.
