CBSE Class 10 Answered

The porphyrins are an enormous group of organic compounds, found all over the living world. A porphyrin is an organic compound that contains four pyrrole rings. A pyrrole is a pentagon-shaped ring of four carbon atoms with a nitrogen atom at one corner. The special thing about porphyrins is that they bind metals. The four nitrogens in the middle of the porphyrin molecule can grab and hold metal ions such as magnesium, iron, zinc, nickel etc.

Depending upon the metal attached, the porphyrin molecule acquires different properties and gets a different name. So, if the central metal is iron (Fe), the porphyrin complex is called heme. Hemoglobin, the molecule in red blood cells that combines with oxygen, has four of these heme groups. The iron ion of the heme group is responsible for binding the oxygen.

Chlorophyll allows plants to capture the sun's energy, and is responsible for plants' green color. It is made up in part of a porphyrin molecule whose central metal ion is magnesium (Mg).

The vitamin B₁₂ consists of a porphyrin molecule with a cobalt ion in the middle