Biological Systems MCAT Practice Exam

Which enzyme catalyzes the conversion of carbon dioxide and water into carbonic acid in red blood cells?

1. Bicarbonate

2. Carbonic anhydrase

3. Hemoglobin

4. Protease

The correct answer is: Carbonic anhydrase

The enzyme that catalyzes the conversion of carbon dioxide and water into carbonic acid in red blood cells is carbonic anhydrase. This enzyme plays a crucial role in regulating pH and facilitating gas exchange in the body. When carbon dioxide produced by metabolizing tissues enters red blood cells, carbonic anhydrase catalyzes the rapid reaction between carbon dioxide and water to form carbonic acid. This reaction is vital for maintaining acid-base balance in the blood and assisting in the transport of carbon dioxide from tissues to the lungs for exhalation. Carbonic acid can further dissociate into bicarbonate and hydrogen ions, which allows for efficient transport of carbon dioxide in the form of bicarbonate ions in the plasma. The presence of carbonic anhydrase ensures that this process occurs quickly, which is essential given the high levels of carbon dioxide produced during cellular metabolism. In contrast, bicarbonate is a product of this reaction, not an enzyme. Hemoglobin is a protein that carries oxygen and can bind carbon dioxide, but it does not catalyze this specific conversion. Proteases are enzymes that break down proteins and are unrelated to the process of converting carbon dioxide and water into carbonic acid. Thus, carbonic anhydrase is