Question

Statements
(A) Carbonic anhydrase is present in the erythrocytes
(B) In erythrocytes the carbon dioxide combine with water and is transported

• A. Statement $\left(\right.A\left.\right)$ is correct and is responsible for statement $\left(\right.B\left.\right)$
• B. Statement $\left(\right.A\left.\right)$ is not correct but statement $\left(\right.B\left.\right)$ is correct
• C. Both statements $\left(\right.A\left.\right)$ and $\left(\right.B\left.\right)$ are wrong
• D. Statement $\left(\right.A\left.\right)$ is correct but not involved in statement $\left(\right.B\left.\right)$

Answer 1

Answer: (A)

After the exchange of gases in the alveolar and tissue level, the gases are transported. Oxygen and carbon dioxide are transported by the blood. There are three main ways CO₂ is transported:

• In dissolved state CO₂ is transported. This accounts for nearly 7% of the total carbon dioxide. The gas gets dissolved in the plasma and is carried as solution. Deoxygenated or venous blood and oxygenated or arterial blood carries about 2.7 mL and 2.4 mL of this gas per 100 mL of blood in dissolved state.
• Major share of this gas is transported as Bicarbonate ( $HCO_{3}^{-}$ ) ions. Nearly 70% of the total gas is transported in this way. This reaction is slow in the plasma and fast in RBC due to carbonic anhydrase enzyme. CO₂ diffuses into the red blood cells and is converted to H⁺ and HCO₃^– by an enzyme called carbonic anhydrase. This HCO₃^– is transported back into the blood via a chloride-bicarbonate exchanger. The HCO₃^– can now act as a buffer against any hydrogen in the blood plasma.

$CO_{2}+H_{2}O\overset{C a r b o n i c a n h y d r a s e}{ \rightarrow }H_{2}CO_{3}\overset{C a r b o n i c a n h y d r a s e}{ \rightarrow }H^{+}+HCO_{3}^{-}$

• Nearly 23% of the gas is transported as Carbamino-haemoglobin and is transported. The gas directly reacts with the amine radical of the protein to form this unstable compound. This is a reversible reaction.

$HHbNH_{2}+CO_{2}\rightleftharpoonsHbNHCOOH+H^{+}$