Question

In what form is the majority of carbon dioxide transported in the blood? a. Bicarbonate ion b. Carbaminohemoglobin c. Carbonic acid d. Carbonic an hydrase

Short answer

Answer: Bicarbonate ion

Step-by-step solution

Understand the options

The four options provided are different forms of carbon dioxide transport in the blood. Let's briefly understand each: a. Bicarbonate ion (HCO3-) is formed when CO2 combines with water (H2O) in the presence of the enzyme carbonic anhydrase. It is a major form of CO2 transport in the blood. b. Carbaminohemoglobin is formed when CO2 reacts with hemoglobin, binding directly to it in the blood. c. Carbonic acid (H2CO3) is formed when CO2 combines with water, but it is an unstable intermediate form that quickly dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+). d. Carbonic anhydrase is an enzyme found in red blood cells that catalyzes the formation of carbonic acid from CO2 and water, which then dissociates into bicarbonate ions and hydrogen ions.

Identify the most prevalent form

Given the information above, we can deduce that the majority of carbon dioxide is transported in the blood as bicarbonate ions (HCO3-). Bicarbonate ions account for up to 70% of the total CO2 transport in the blood. Carbaminohemoglobin and carbonic acid account for smaller percentages, and carbonic anhydrase is an enzyme involved in the process, but is not a form of CO2 transport itself.

Select the correct answer

Therefore, based on the information provided, the correct answer is: a. Bicarbonate ion

Key concepts

Bicarbonate ion

Bicarbonate ions, represented scientifically as \(\text{HCO}_3^-\), play a crucial role in the transportation of carbon dioxide (\(\text{CO}_2\)) within the blood. When carbon dioxide enters the bloodstream, it interacts with water (\(\text{H}_2\text{O}\)). This reaction is significantly accelerated by the presence of the enzyme carbonic anhydrase, resulting in the formation of carbonic acid (\(\text{H}_2\text{CO}_3\)). However, carbonic acid is highly unstable and rapidly dissociates into bicarbonate ions and hydrogen ions (\(\text{H}^+\)).

• The bicarbonate ions are the primary mode of transport for carbon dioxide in the blood, accounting for approximately 70% of the total carbon dioxide transported.
• The chemical reaction can be summarized as follows: \[ \text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+\]
• This equilibrium reaction ensures efficient transport and release of carbon dioxide depending on the physiological needs of the body, such as exhalation.

The conversion into bicarbonate ions not only helps in transporting carbon dioxide but also plays a role in maintaining the pH balance of the blood. The bicarbonate buffer system is essential in regulating acidity, providing stability for essential physiological processes.

Carbaminohemoglobin

Carbaminohemoglobin is another important form of carbon dioxide transport in the blood. This molecule forms when carbon dioxide binds directly with hemoglobin, a protein within red blood cells responsible for carrying oxygen.

• This process does not involve carbonic anhydrase or water, making it a distinct method of carbon dioxide transport.
• In this mechanism, carbon dioxide attaches to the amino groups of the hemoglobin, creating carbamino compounds.
• Carbaminohemoglobin is responsible for approximately 23% of the carbon dioxide transport within the bloodstream.
• The binding of carbon dioxide reduces hemoglobin's affinity for oxygen, a phenomenon known as the Bohr effect, enhancing oxygen release where it is needed most.

Unlike oxygen, which binds to the iron in hemoglobin, carbon dioxide interacts with the protein structure itself, thus not competing directly with oxygen but rather influencing its transport through physiological effects.

Carbonic anhydrase

Carbonic anhydrase is a vital enzyme that facilitates one of the most crucial reactions within the human body for gas transport. Present in red blood cells, this enzyme accelerates the reaction between carbon dioxide and water.

• It rapidly catalyzes the conversion of carbon dioxide and water to carbonic acid, which then dissociates into bicarbonate ions and hydrogen ions:
• \[\text{CO}_2 + \text{H}_2\text{O} \xrightarrow{\text{Carbonic Anhydrase}} \text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+\]
• The enzyme’s primary function is to speed up this reaction, facilitating efficient CO2 transport and aiding in regulatory processes, like blood pH balance.
• Without carbonic anhydrase, the process would be significantly slower, impeding the body's ability to handle carbon dioxide effectively during respiration.

This enzyme's presence underscores the complexity of cellular processes, highlighting how biological catalysts are essential for maintaining life-sustaining functions efficiently.