CH=CH. CH CH N N一Fe—N N CH C C CH=CH CH CH CH 3 N CH O Globin polypeptide Hemoglobin is the gas-transport molecule inside erythrocytes Oxygen binds to the iron atom. Heme attaches to a polypeptide chain subunits bind to each other to make a single hemoglobin molecule o by a nitrogen atom to form one subunit of hemoglobin. Four of thesHemoglobin is the gas-transport molecule inside erythrocytes. Oxygen binds to the iron atom. Heme attaches to a polypeptide chain by a nitrogen atom to form one subunit of hemoglobin. Four of these subunits bind to each other to make a single hemoglobin molecule