Porphyrin is a compound

made of four pyrrole rings

The internal machinery of life “the chemistry of the parts is something beautiful.”

Richard P. Feynman, The Meaning of It All: Thoughts of a Citizen-Scientist. (1998), pp.11-12

pyrrole rings

of four pyrrole rings

Fe	Co	Mg
IRON	COBALT	MAGNESIUM
heme	B-12	chlorophyll
oxygenates blood	vitamin	essential to photosynthesis

Porphyrin is a flat molecule that can act as a tetradentate (i.e., four nitrogen "teeth") chelating molecule for metals such as Mg, Fe, Zn, Ni, Co, Cu, & Ag (i.e., has "claw" that can grab and hold these metals). The red arcs represent the electrostatic interaction of the nitrogen's electrons. If the central metal is iron, the resulting iron porphyrin complex is the the heme group. There are four heme groups in hemoglobin in your blood. Heme is also the key part of enzymes like peroxidase, catalase, and cytochrome c. (In most heme compounds the iron picks up a top and a bottom atom producing a 6-coordinate, octahedral complex, rather than the square-planar 4-coordinate bare porphyrin.) A magnesium porphyrin complex is the heart of chlorophyll, the active molecule of photosynthesis.