What is heme?

What is heme?

• A. This porphyrin contains iron and binds oxygen to hemoglobin.
• B. A nitrogen-containing ring hydrocarbon molecule.
• C. A carbohydrate used for energy storage.
• D. A mineral cofactor.

Answer: (A)

Heme is an iron-containing porphyrin prosthetic group that sits in hemoglobin and provides the site where oxygen binds. The porphyrin ring coordinates a central iron ion, and this iron reversibly binds oxygen, allowing hemoglobin to pick up O2 in the lungs and release it in tissues. This distinguishes it from simple nitrogen-containing hydrocarbons or carbohydrates, and from a vague mineral cofactor—the essential feature is the iron within the planar, four-pyrrole-ring structure of the porphyrin.

Heme is an iron-containing porphyrin prosthetic group that sits in hemoglobin and provides the site where oxygen binds. The porphyrin ring coordinates a central iron ion, and this iron reversibly binds oxygen, allowing hemoglobin to pick up O2 in the lungs and release it in tissues. This distinguishes it from simple nitrogen-containing hydrocarbons or carbohydrates, and from a vague mineral cofactor—the essential feature is the iron within the planar, four-pyrrole-ring structure of the porphyrin.