This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: HAEM synth and porphyrias, Subject name: Biochemistry
Heme is which porphyrin: 
Select and explain. 
A. Type I, B. Type II, C. Type III, D. Type IV
C: Type III
Answer: C: Type III 
Explanation: The side chain groups in porphyrins may be arranged in four different structural configurations (I to IV). Only type I and type III series are found in nature and the porphyrins of type III series are not only more abundant but are also physiologically impoant in humans. Haem is a type III porphyrin.