Video Transcript
The diagram provided shows a basic
outline of the Krebs cycle. What are the products of the Krebs
cycle? (A) ATP, reduced FAD, reduced NAD,
and carbon dioxide. (B) ADP, FAD plus, and NAD
plus. (C) Oxaloacetic acid and acetyl
coenzyme A. (D) Carbon dioxide and acetyl
coenzyme A.
The Krebs cycle is the third major
stage of cellular respiration. Let’s briefly recap the other
stages to see where this cycle fits in. Firstly, glycolysis takes a
molecule of glucose and, through a series of biochemical reactions, converts it into
two molecules of pyruvate. Then, the link reaction converts a
molecule of pyruvate into a compound called acetyl coenzyme A. Acetyl coenzyme A then becomes the
primary reactant of the Krebs cycle, also known as the citric acid cycle. After the Krebs cycle, the final
stage of cellular respiration is oxidative phosphorylation. But we won’t worry about this too
much for now.
Let’s take a look at the diagram to
determine what the products of the Krebs cycle are. Firstly, the two-carbon acetyl
coenzyme A joins with a four-carbon compound called oxaloacetic acid. You may also see this called
oxaloacetate. This forms a six-carbon compound
called citric acid or citrate. So far, no products have been given
out by the Krebs cycle. Next, citric acid is converted into
a five-carbon compound. We can see two molecules are
produced in this process, one molecule of carbon dioxide and one molecule of reduced
NAD. Let’s use this table to continue to
record the products of the Krebs cycle.
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, another molecule of
carbon dioxide, and one molecule of ATP. Our new four-carbon compound is now
converted into oxaloacetic acid. As this happens, we see that
another molecule of reduced NAD is produced and one molecule of reduced FAD. Finally, we’ve come full circle
around the Krebs cycle. So let’s see, using our tally of
products, what our correct answer is. The only option to correctly show
all of the products of the Krebs cycle is option (A): ATP, reduced FAD, reduced NAD,
and carbon dioxide.
