Question

Which of the following occurs in hemoglobin upon oxygen binding?

a) The heme Fe²⁺ is pulled towards the plane of the heme group
b) The His coordinated to the heme Fe²⁺ is pulled towards the heme group
c) The central cavity between the four subunits is decreased in size
d) Hemoglobin changes from the T state to the R state

Answer 1

Upon oxygen binding to hemoglobin, the heme Fe²⁺ ion moves towards the plane of the heme group, and hemoglobin transitions from the T state to the R state, increasing its oxygen affinity.

Step-by-step explanation:

Upon oxygen binding to hemoglobin, several events occur to facilitate the transportation of oxygen through the blood. One of the events that takes place is:

• The heme Fe²⁺ is pulled towards the plane of the heme group.

This is part of the cooperative binding process that alters the quaternary structure of hemoglobin. Specifically:

• Hemoglobin changes from the T state to the R state (tense state to relaxed state), which enhances its ability to bind more oxygen molecules. This conformational shift is attributed to the affinity increase for oxygen as other heme sites get occupied.

The increased affinity and subsequent binding causes hemoglobin to undergo a structural change, through which the Fe²⁺ ion is drawn into the plane of the heme, allowing for further oxygen binding. While the central cavity may slightly change, and the movement of His is involved, they are not the primary changes upon initial oxygen binding.