How Does Hemoglobin Help Us Breathe? Part II-
the heme

There was a solution, and it was a chemical one. If Oxygen was bound to a chemical such as iron using a covalent [LINK] bond, the strongest of molecular connections, then more oxygen could get in, -- you wouldn't need it in the spacing-taking gas form; it could be moved as a solid. A protein called a heme that carries Oxygen bound to iron is found by the time worms crawled the earth.

The heme is made of a ring structure with an iron atom at the center. The iron gives hemoglobin its color, just as it gives the red soils of the American Southwest their color, too. The four hemes are "cooperative" with each other. The first Oxygen has a hard time attaching, but once it is in the next attachment is easier, the next easier yet, and the last very easy. Hemoglobin has, then, two shapes, one receptive to Oxygen (R state) and one stable and unreceptive (T state).

The process of combining of of a metal such as iron with Oxygen is called oxidation. Rust is a good example of this combination. But why wasn't it enough to have iron powder in the blood? Having the heme was not enough for larger animals.

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