<prompt> The heme portion of the hemoglobin molecule consists of:Porphyrin ring with a molecule of Fe in the centerA polypeptide chain containing FeA pyrole ring with four molecules of Fe in the centerFour porphyrin rings, each containing a molecule of Fe in the center  <response>: Structurally, porphyrin consists of four pyrrole rings five-membered closed structures containing one nitrogen and four carbon atoms linked to each other by methine groups CH.The iron atom is kept in the centre of the porphyrin ring by interaction with the four nitrogen atoms. 