Question

Which of the following occurs in hemoglobin upon oxygen binding?

a) The heme Fe(2+) is pulled into the plane of the heme group
b) The His coordinated to the heme Fe(2+) is pulled towards the heme group
c) The central cavity between the four subunits is increased in size
d) Hemoglobin changes from the T state to the R state
e) All of the above

Answer 1

When oxygen binds to hemoglobin, several adjustments occur, including the Fe2+ being pulled into the plane of the heme group, the proximal His shifting position, the expansion of the central cavity, and the protein transitioning from the T to the R state.

Step-by-step explanation:

Upon oxygen binding to hemoglobin, several changes occur at the molecular level:

• (a) The heme Fe2+ is pulled into the plane of the heme group, allowing for a more efficient binding of oxygen.
• (b) The His coordinated to the heme Fe2+ is pulled towards the heme group, altering the conformation of the protein.
• (c) The central cavity between the four subunits is increased in size, aided by the conformational changes induced by oxygen binding.
• (d) Hemoglobin changes from the T (tense) state to the R (relaxed) state, facilitating the cooperative binding of oxygen molecules.

Together, these changes enhance hemoglobin's ability to bind and transport oxygen. Thus, the correct answer is (e) All of the above.