For each turn of the Krebs cycle,
how many molecules of ATP are produced?
This question asks us about the
Krebs cycle, which is one of the stages in cellular respiration. Cells perform cellular respiration
in order to extract energy from sugar and transfer this energy to a molecule called
ATP. There are four stages in cellular
respiration. These stages are glycolysis, the
link reaction, the Krebs cycle, and oxidative phosphorylation.
The question is asking us about the
third stage in respiration: the Krebs cycle. So let’s have a closer look at the
Krebs cycle. The Krebs cycle takes place in the
mitochondria. The product of the link reaction, a
two-carbon compound called acetyl coenzyme A, enters the Krebs cycle. This two-carbon compound joins with
the four-carbon compound oxaloacetic acid to produce citric acid, which has six
carbons. Citric acid then undergoes a series
of reactions, eventually reforming oxaloacetic acid.
So what is the point of the Krebs
cycle if the intermediate compounds continually cycle? Well, the series of reactions in
the cycle both produce ATP and reduce the coenzymes NAD and FAD. Reduced NAD and FAD are crucial for
the next, and final, stage of aerobic cellular respiration, which is oxidative
phosphorylation. This is the stage in respiration
where the majority of ATP is produced, the ultimate aim of the entire process.
Now that we have reviewed the Krebs
cycle, let’s take another look at our question. We are asked for each turn of the
Krebs cycle, how many molecules of ATP are produced. We can see from the diagram that
one molecule of ATP is produced per turn. So the correct answer is one.