For 10 points, name this family of chemicals with a metal-coordinating ring structure, examples of which include chlorophyll and heme.
Dimeric arrays in which this molecule exists in zinc-bonded and free-base forms are capable of long-distance energy migration and have been used in artificial olfactory receptors.  Cationic manganese examples of these act as superoxide reductases.  One piece of evidence for the RNA world hypothesis is that bacteria and plants, but not humans, use glutamyl-tRNA in the C-5 pathway for the synthesis of the committed precursor of this family of compounds; in humans, glycine reacts with succinyl-CoA to form alpha-amino-beta-ketoadipate, which is decarboxylated to form the committed precursor D-aminolevulinate.  The addition of iron to one member of this family of compounds is catalyzed by ferrochelatase.  Defects in an early step in their biosynthesis can result in X-linked sideroblastic anemia.  For 10 points, name this family of chemicals with a metal-coordinating ring structure, examples of which include chlorophyll and heme.
Dimeric arrays in which this molecule exists in zinc-bonded and free-base forms are capable of long-distance energy migration and have been used in artificial olfactory receptors.  
porphyrins