Question

When we exhale we expire CO2 as a byproduct of our cellular respiration. What are the specific enzymes that are responsible for catalyzing the production of CO2 in cellular metabolism (explain clearly for full points). (3pts)

Answer 1

Carbohydrates, proteins and fats are all used by the body as fuels in cellular respiration. However, the major source is glucose. Glucose is broken down to carbon dioxide and water, with the formation of ATP. Carbon dioxide formed is exhaled out by the lungs as a water product.

There are 6 molecules of CO2 produced per glucose. Glucose is broken down to two pyruvate molecules by glycolysis. Each pyruvate is converted to acetyl CoA by accepting CoA. In this process carbon dioxide is released/removed from pyruvate. The enzyme involved is pyruvate dehydrogenase. NAD+ is converted to NADH.

The Krebs cycle or TCA cycle produces the rest CO2 during cellular respiration. The step 3 and 4 of TCA cycle produce CO2.

Step 3: Alpha ketoglutarate is formed when isocitrate is oxidized by isocitrate dehydrogenase. In this process, NAD+ is converted to NADH and CO2 is released.

Step 4: Alpha ketoglutarate is then converted to succinyl CoA by alpha ketoglutarate dehydrogenase. This is a redox reaction where NADH is formed from NAD+. CoA is added and there is a release of CO2 in the process.

Each of these steps produce 1 CO2 each (pyruvate to acetyl CoA, isocitrate to alpha ketoglutarate, alpha ketoglutarate to succinyl CoA). As there are two pyruvate molecules formed from 1 glucose, the total CO2 formed from glucose is 6.

In liver, ethanol is metabolized to acetaldehyde, which is then converted to acetate by aldehyde dehydrogenase. Acetate can then be converted to carbon dioxide and water, mostly by other tissues.