Question

When hemoglobin is converted from the deoxy (T) form to oxyhemoglobin (R), A. it becomes more acidic and releases protons. B. carbamino formation is promoted. C. binding of 2,3 -bisphosphoglycerate (BPG) is favored. D. bound NO is transferred to glutathione. E. all of the above.

Short answer

Answer: The correct answer is D: "bound NO is transferred to glutathione" as it is the only option that accurately describes a change occurring when hemoglobin is converted from the deoxy (T) form to oxyhemoglobin (R).

Step-by-step solution

Understanding hemoglobin conversion

Hemoglobin is a protein in red blood cells responsible for carrying oxygen from the lungs to the rest of the body. It can exist in two forms: the deoxy form (T) that doesn't have oxygen bound and the oxyhemoglobin form (R) that has oxygen bound. The conversion between these two forms involves changes in the protein structure and its interactions with other molecules.

Option A: Acidity and proton release

When hemoglobin binds to oxygen, it undergoes a conformational change which helps release protons. This makes the hemoglobin molecule less acidic, not more acidic. Therefore, option A is incorrect.

Option B: Carbamino formation promotion

Carbamino formation refers to the binding of carbon dioxide (CO2) to hemoglobin. The deoxy form (T) of hemoglobin has a higher affinity for CO2, promoting carbamino formation. When it binds to oxygen and converts to the oxyhemoglobin form (R), it releases CO2. So, option B is also incorrect.

Option C: Binding of 2,3-bisphosphoglycerate (BPG)

2,3-bisphosphoglycerate (BPG) is a molecule that stabilizes the deoxy form (T) of hemoglobin, thus favoring the release of oxygen. When hemoglobin binds to oxygen, its affinity for BPG decreases, so the binding of BPG is not favored in the oxyhemoglobin form (R). Hence, option C is incorrect.

Option D: Bound NO transferred to glutathione

Nitric oxide (NO) can bind to hemoglobin and be transferred to glutathione, effectively reducing its vasoconstriction effects. This transfer occurs when hemoglobin is in the R state; therefore, option D correctly describes a change that occurs during the conversion from the deoxy (T) form to oxyhemoglobin (R).

Option E: All of the above

Since options A, B, and C are incorrect, option E, which states that all of the options are correct, is also incorrect.

Answer

The correct answer to the question is D: "bound NO is transferred to glutathione" as it is the only option that accurately describes a change occurring when hemoglobin is converted from the deoxy (T) form to oxyhemoglobin (R).

Key concepts

Oxygen Transport in Blood

Our remarkable bloodstream, a highway for essential molecules, employs hemoglobin as the primary vehicle for oxygen transport from our lungs to the entirety of our body. Hemoglobin, found in the red blood cells, performs exceptional feats of binding and releasing oxygen based on the body's demand.

Oxygen molecules hitch a ride on hemoglobin through a fascinating process. Each hemoglobin molecule is equipped with four heme groups, and it's here that oxygen molecules make a temporary but vital bond. When hemoglobin breezes through the oxygen-rich environment of the lungs, it transforms into oxyhemoglobin, its oxygen-laden form, by snapping up oxygen molecules. Once it travels to oxygen-starved tissues, the bond loosens, delivering the much-needed oxygen.

This cycle is critical for survival, maintaining optimum levels of oxygen throughout the tissues of the body. It's akin to a delivery service that picks up and drops off parcels at various destinations – in this case, the precious cargo is life-sustaining oxygen.

Hemoglobin Structure Changes

Hemoglobin's ability to transport oxygen is owed to its dynamic structure, which undergoes meticulous changes enabling it to pick up and release oxygen effectively. In its deoxy form, known as the T (tense) state, hemoglobin is like a relaxed hand, not holding onto anything. Without oxygen, its structure is primed to pick up the next batch of oxygen molecules in the lungs.

Once oxygen enters the scene, the entire scene shifts as hemoglobin transitions to the R (relaxed) state forming oxyhemoglobin - akin to a hand now firmly grasping the objects it once hovered over. This structural transformation involves the iron atoms within the heme groups moving and creating the perfect seat for oxygen molecules.

Understanding this structural ballet is crucial, as it drives home the incredible precision with which hemoglobin operates. It's a meticulously choreographed dance between taking on oxygen when needed and releasing it when the body calls for it.

Hemoglobin Oxygen Affinity

The performance of hemoglobin can be measured by its oxygen affinity, essentially its attraction to oxygen. Various factors influence hemoglobin's eagerness or reluctance to bond with oxygen. These factors include the concentration of hydrogen ions (pH), levels of carbon dioxide, temperature, and the presence of 2,3-bisphosphoglycerate (BPG), a molecule produced by red blood cells.

Consider the affinity like a love story: under certain conditions, hemoglobin eagerly embraces oxygen, while other times, it's more standoffish. In the acidic environment produced by high levels of carbon dioxide, or in the presence of BPG, hemoglobin's affinity diminishes, favoring oxygen release to the tissues. Conversely, in the lungs where conditions are inverse, affinity increases, allowing oxygen to bind meticulously.

This delicate balance ensures that oxygen is picked up where it's plentiful and released where it's scarce, a fine-tuned mechanism that sustains life on a breath-by-breath basis.