Final answer:
Heme is composed of iron and protoporphyrin, and it is found in proteins such as hemoglobin and myoglobin.
Step-by-step explanation:
Heme is composed of iron and protoporphyrin. It is an iron porphyrin structure that is synthesized in the reticuloendothelial cells (bone marrow) of adult human beings. Protoporphyrin is a type of porphyrin that is present in heme. In addition, heme is also found in proteins such as hemoglobin and myoglobin, but it is the combination of iron and protoporphyrin that defines the composition of heme.