Identify the true statements regarding the heme group of myoglobin and hemoglobin:
a. a heme group contains four pyrrole rings, which are linked via methene (methine) bridges.
b. the cooperativity of oxygen binding in hemoglobin arises from a shorter Fe-O₂ bond length in the T state compared to the R state.
c. The globin chains of myoglobin and hemoglobin prevent the oxidation of Fe²⁺ to Fe³⁺, which irreversibly binds oxygen.
d.the R state of hemoglobin has greater affinity for O₂ than the T state because the iron atom is in the plane of the porphyrin ring.
e. The heme group is conjugated.
f. Myoglobin contains one heme group.
g. the iron in the heme group can form six bonds. The fifth is with an imidazole ring of a histidine, and the sixth is with oxygen.
