In which state does hemoglobin have a higher affinity for oxygen?

Hemoglobin exhibits two primary conformations: the tense (T) state and the relaxed (R) state. The correct answer is the relaxed (R) state, as this conformation has a higher affinity for oxygen.

In the R state, hemoglobin's structure allows for a better fit for oxygen molecules, making it more likely to bind to them. This increased affinity is a critical aspect of oxygen transport, as it enables hemoglobin to pick up oxygen in the lungs, where oxygen concentration is high, and release it in tissues, where it is needed and oxygen concentration is lower.

The T state, on the other hand, has a lower affinity for oxygen. This state is favored in conditions where oxygen is released, such as in metabolically active tissues. The transition from the T state to the R state is brought about by the binding of oxygen, which stabilizes the R conformation and facilitates further oxygen binding in a cooperative manner.

Understanding the dynamics between these states is key to grasping how hemoglobin efficiently transports oxygen throughout the body.