n hemoglobin, the transition from the low affinity T state to high affinity R state is triggered by: A. Fe2 binding B. Heme binding C. Oxygen binding D. Subunit association E. Subunit dissociation

Answer: C). Oxygen binding

Explanation: Hemoglobin is a protein present in the red blood cells that transports oxygen to the body cells and tissues. Hemoglobin has four subunits with four binding sites: one binding site on each protein subunit. Hemoglobin exists in two states: the tensed (T) state and the relaxed (R) state. The T state has low affinity for oxygen while the R state has high affinity for oxygen. The binding of oxygen to the T state triggers a conformational change in the protein and its transition to R state. The binding of oxygen to one binding site on hemoglobin increases the binding of oxygen to the remaining subunits, this phenomenon is known as cooperativity.