Problem 26 - Anatomy and Physiology of Animals

Question

Which reaction is catalyzed by carbonic anhydrase? a. \(\mathrm{HPO}_{4}^{2-}+\mathrm{H}^{+} \leftrightarrow \mathrm{H}_{2} \mathrm{PO}_{4}\) b. \(\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \leftrightarrow \mathrm{H}_{2} \mathrm{CO}_{3}\) c. \(\mathrm{H}_{2} \mathrm{PO}_{4}-\mathrm{OH}^{-} \leftrightarrow \mathrm{HPO}_{4}^{2}-\mathrm{H}_{2} \mathrm{O}\) d. \(\mathrm{H}_{2} \mathrm{CO}_{3} \leftrightarrow \mathrm{HCO}_{3-}+\mathrm{H}^{+}\)

Step-by-Step Solution

Answer

Option (b) is catalyzed by carbonic anhydrase.

Step 1: Identify the Function of Carbonic Anhydrase

Carbonic anhydrase is a well-known enzyme that catalyzes the interconversion between carbon dioxide and water to form carbonic acid (\( \mathrm{H}_{2} \mathrm{CO}_{3} \)). Therefore, we need to match this reaction with the options given.

Step 2: Match the Reaction to the Options

The enzyme catalyzes the reaction \( \mathrm{CO}_{2} + \mathrm{H}_{2} \mathrm{O} \leftrightarrow \mathrm{H}_{2} \mathrm{CO}_{3} \). We need to see which option states exactly this or a very close form of this reaction.

Step 3: Focus on Option (b)

Option (b) describes the reaction: \( \mathrm{CO}_{2} + \mathrm{H}_{2} \mathrm{O} \leftrightarrow \mathrm{H}_{2} \mathrm{CO}_{3} \). This matches perfectly with the reaction catalyzed by carbonic anhydrase.

Key Concepts

Enzyme Function

Enzymes are fascinating biological molecules. They're proteins that speed up chemical reactions without being consumed in the process. This special ability is called catalysis. Enzymes significantly lower the energy needed for reactions to occur—this is known as the activation energy. By doing so, they allow reactions to proceed faster and more efficiently than they would without the enzyme.
Enzymes are highly specific. Each enzyme catalyzes a particular reaction or set of reactions. This specificity is due to the unique shape of the enzyme's active site, which is where the reaction occurs. The active site is like a lock, while the substrate—the molecule the enzyme acts on—fits into it like a key. This ensures that enzymes facilitate the correct chemical pathways needed for life's processes.

• E.g., Carbonic Anhydrase is an enzyme with a specific role in converting carbon dioxide and water into carbonic acid.
• The speed of the reaction is increased, aiding processes essential for life, like respiration.

Catalyzed Reaction

When we say a reaction is catalyzed, it means an enzyme is making it happen faster. The term comes from the Greek word 'katalysis,' meaning to dissolve or break down. In biology, catalyzed reactions are crucial since many of them would naturally occur far too slowly to sustain life processes.
In the reaction catalyzed by the enzyme carbonic anhydrase, carbon dioxide ( CO_2 ) and water ( H_2O ) are rapidly converted into carbonic acid ( H_2CO_3 ). This catalysis is strikingly efficient, with the enzyme speeding up the reaction up to one million times faster, illustrating just how powerful enzymes can be!
Let's break it down further:

• Substrate: Carbon dioxide and water are the substrates for this reaction.
• Product: The result is carbonic acid, which can rapidly turn into bicarbonate and a proton, impacting the acid-base balance in the blood.

Without enzymes like carbonic anhydrase, the conversion would be slow, hampering physiological functions like gas exchange.

Carbon Dioxide Conversion

Carbon dioxide conversion is a critical biochemical process, especially in the context of respiration. It's the process by which carbon dioxide produced in cells during metabolism is converted quickly to other forms that can be transported by blood.
In this reaction, carbon dioxide combines with water—a reaction facilitated by the enzyme carbonic anhydrase—to become carbonic acid ( H_2CO_3 ). From here, carbonic acid often dissociates into bicarbonate ( HCO_3^- ) and a hydrogen ion ( H^+ ).
The process has several essential roles:

• Regulating pH: The formed bicarbonate ion is a major component in the body's buffering system, which helps regulate pH levels in blood and tissues.
• Respiration: It enables effective transport of CO_2 from body tissues to lungs, where it is exhaled.
• Maintaining balance: Assists in maintaining the balance of ions in cells, crucial for cellular activities.

This conversion ensures that carbon dioxide, a waste product, is efficiently processed and expelled, sustaining cellular and whole-body homeostasis.