The portal has been deactivated. Please contact your portal admin.

Question Video: Recalling How Many Molecules of Carbon Dioxide are Released by the Krebs Cycle Biology

For each turn of the Krebs cycle, how many molecules of CO₂ are released?

02:26

Video Transcript

For each turn of the Krebs cycle, how many molecules of CO2 are released?

Cellular respiration is an important process in all living organisms. It is the process in which glucose is broken down to release energy that is then stored in molecules of ATP. There are four main steps in cellular respiration: glycolysis, the link reaction, Krebs cycle, also known as the citric acid cycle, and oxidative phosphorylation, also known as the electron transport chain.

During glycolysis, glucose is converted into pyruvate in the cytoplasm. Then in the link reaction, this pyruvate is moved into the mitochondrion where it is converted into acetyl coenzyme A, or acetyl-CoA. This acetyl-CoA is a reactant that then enters the Krebs cycle in the mitochondrion. In the first step, the four-carbon molecule oxaloacetic acid reacts with the two-carbon molecule acetyl-CoA to form the six-carbon molecule citric acid. Then, the six-carbon molecule citric acid breaks down and releases a molecule of carbon dioxide to form the five-carbon molecule ketoglutaric acid. This also reduces a molecule of NAD+ to NADH.

Next, the five-carbon molecule ketoglutaric acid breaks down to form the four-carbon molecule succinic acid, releasing a molecule of carbon dioxide in the process. A molecule of NAD+ is reduced to NADH and a molecule of ATP is also formed in this step.

Next, the four-carbon molecule succinic acid is converted into the four-carbon molecule malic acid. This process reduces a molecule of FAD to FADH2 and uses a molecule of water. Then the four-carbon molecule malic acid is converted into the four-carbon molecule oxaloacetic acid while reducing a molecule of NAD+ to NADH. This completes one turn of the Krebs cycle. You’ll notice that one turn of the Krebs cycle produces two molecules of carbon dioxide as indicated here.

Therefore, the correct answer is two molecules.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.