Which of the following molecule/ion is not transported/buffered by hemoglobin?
Show Hint
Think of hemoglobin's main jobs: gas transport (O\(_2\), CO\(_2\)) and pH buffering (H\(^+\)). Common electrolytes like Na\(^+\), K\(^+\), and Cl\(^-\) are generally handled by membrane pumps and channels, not by hemoglobin.
Step 1: Understanding the Concept:
Hemoglobin (Hb) is a protein in red blood cells that has several crucial roles in respiratory gas transport and blood pH regulation. We need to identify which of the given options is not involved in these functions. Step 2: Detailed Explanation:
Let's examine the interaction of hemoglobin with each molecule/ion:
O\(_2\): This is the primary function of hemoglobin. It binds reversibly to the heme iron in Hb to transport oxygen from the lungs to the tissues.
CO\(_2\): Hemoglobin transports a fraction (about 20-25\%) of carbon dioxide directly. CO\(_2\) binds to the amino groups of the globin chains to form carbaminohemoglobin.
H\(^+\): Hemoglobin is a major blood buffer. Deoxyhemoglobin has a higher affinity for protons (H\(^+\)) than oxyhemoglobin. It binds H\(^+\) ions produced from the dissociation of carbonic acid, thus helping to maintain blood pH. This is part of the Bohr effect.
Na\(^+\): Sodium ions (Na\(^+\)) are crucial for maintaining osmotic balance and membrane potential in cells, including red blood cells. However, their transport and concentration are regulated by pumps (like Na\(^+\)/K\(^+\)-ATPase) and channels, not by binding to hemoglobin.
Step 3: Final Answer:
Hemoglobin transports O\(_2\) and CO\(_2\), and buffers H\(^+\). It does not transport or buffer Na\(^+\) ions.
