Question

The hydration product formed during carbon dioxide transport in the blood is

• A. Acetic acid
• B. Lactic acid
• C. Citric acid
• D. Carbonic acid

Hint:

Carbonic anhydrase is one of the fastest enzymes known, increasing the rate of carbon dioxide hydration by up to a million-fold compared to the uncatalyzed reaction.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Carbon dioxide (\(\text{CO}_2\)) is a waste product of cellular respiration that must be transported from peripheral tissues to the lungs for excretion.
It is transported in the blood in three primary forms: dissolved in plasma, bound to hemoglobin as carbamino compounds, or as bicarbonate ions (\(\text{HCO}_3^-\)).

Step 2: Detailed Explanation:
The majority of carbon dioxide (about \(70\%\)) is transported as bicarbonate ions.
This pathway relies on the hydration of carbon dioxide within red blood cells:
Dissolved \(\text{CO}_2\) diffuses from tissue cells into erythrocytes.
Inside the erythrocyte, \(\text{CO}_2\) reacts with water (\(\text{H}_2\text{O}\)) to form Carbonic acid (\(\text{H}_2\text{CO}_3\)).
This hydration reaction is catalyzed by the enzyme carbonic anhydrase: \[ \text{CO}_2 + \text{H}_2\text{O} \xrightleftharpoons{\text{Carbonic Anhydrase}} \text{H}_2\text{CO}_3 \]
Carbonic acid is a weak acid that rapidly dissociates into hydrogen ions (\(\text{H}^+\)) and bicarbonate ions (\(\text{HCO}_3^-\)): \[ \text{H}_2\text{CO}_3 \xrightleftharpoons{\quad} \text{H}^+ + \text{HCO}_3^- \]
The bicarbonate then leaves the erythrocyte via a chloride-bicarbonate exchanger (the chloride shift) to be carried in the plasma.
Therefore, the initial hydration product formed during this process is carbonic acid.

Step 3: Final Answer:
The hydration product formed during carbon dioxide transport is carbonic acid.