Question Video: Recalling How Many Molecules of Reduced NAD Are Produced per Turn of the Krebs Cycle Biology

Video Transcript

For each turn of the Krebs cycle, how many molecules of reduced NAD are produced?

Cellular respiration is the process used by cells to release energy from sugars. The general, overall equation for cellular respiration is glucose plus oxygen forms carbon dioxide plus water. Energy is released during this process in the form of ATP. Cellular respiration occurs in four main stages: glycolysis, the link reaction, the Krebs cycle, and finally oxidative phosphorylation.

The Krebs cycle is the third stage of cellular respiration. Let’s have a look at the Krebs cycle in a bit more detail. Here, we have a diagram to show the basic outline of the Krebs cycle. By going through each reaction sequentially, we can count how many molecules of reduced NAD are produced in one full turn. Firstly, the two carbon acetyl coenzyme A joins with a four carbon compound called oxaloacetic acid, which is sometimes called oxaloacetate. This form is a six-carbon compound called citric acid, or citrate. So far, no molecules of NAD have been reduced.

Next, citric acid is converted into a five-carbon compound. We can see that one molecule of reduced NAD is produced in this process. Now, this five-carbon compound is converted into a four-carbon compound. As we can see from the diagram, this conversion results in another molecule of reduced NAD being produced. Our new four-carbon compound is now converted into oxaloacetic acid. As this happens, we can see that another molecule of NAD is reduced. And as oxaloacetic acid is our final molecule, we have come full circle through the Krebs cycle.

So using this information, we can tally up the total amount of reduced NAD produced by one turn of the Krebs cycle. Our correct answer is three molecules of reduced NAD are produced.