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.