Question

The enzyme essential for the transport of $C{O}_2$ as bicarbonate in blood is

• A. carboxypeptidase
• B. succinic dehydrogenase
• C. carbonic anhydrase
• D. thrombokinase
• E. lactase

Answer 1

Answer: (C)

The large fraction of carbon dioxide (about 70%) is converted to bicarbonate ions ($HC{O}_3^{-}$) and transported in plasma. When carbon dioxide diffuses into the RBCs, it combines with water, forming carbonic acid ($H_{2}C{O}_3$). $H_{2}C{O}_3$ is unstable and quickly dissociates into hydrogen ions and bicarbonate ions.
$\underset{\stackrel{\text{Carbon}}{\mathrm{dioxide}}}{C{O}_2}+\underset{\text{Water}}{H_{2}O}\stackrel{\text{Carbonic anhydrase }}{\rightleftharpoons }\underset{\stackrel{\text{Carbonic}}{\mathrm{acid}}}{H_{2}C{O}_3}$
$\rightleftharpoons \underset{\stackrel{\text{Hydrogen}}{\mathrm{ion}}}{H^{+}}+\underset{\stackrel{\text{Bicarbonate}}{\mathrm{ion}}}{HC{O}_3^{-}}$
This reaction is thousands times faster in erythrocytes because they contain carbonic anhydrase, an enzyme that reversibly catalyses the conversion of carbon dioxide and water to carbonic acid.