Complete the sentences about heme. some terms will not be used. the prosthetic group of hemoglobin and myoglobin is . the organic ring component of heme is . under normal conditions, the central atom of heme is . in , the central iron atom is displaced 0.4 å out of the plane of the porphyrin ring system. the central atom has bonds: to nitrogen atoms in the porphyrin, one to a residue, and one to oxygen. heme porphyrin fe2+fe2+ oxyhemoglobin six four cysteine