HEMOGLOBIN

Most of us know that hemoglobin carries oxygen from the lungs to tissues. Some of us know that it carries CO2 from the tissues back to the lungs and kidneys. Fewer know that hemoglobin is made of four sub-units, 2 alpha units and 2 beta units, that assemble in such a way that a perfect basket-like space for the oxygen is made in the center.

Hemoglobin is rather like a car, or at least a "go-cart". It is made of:
o 2 proteins strands (another production line) globulus
o Heme like chlorophyll complex organic molecule (12 reactions to make heme) 12 genes
o Iron (pomegranate, food and water)

All proteins are made of these alpha and beta strands. Each strand is a polypeptide, a long many beaded chain of amino acids. Each of the four units is made of 146 amino acid links. These strands fold to the required shape. It was one of the very first proteins to have its 3-D structure mapped. The hero was Max Perutz and his colleagues, working in the late 50s at Cambridge University.

The center, called a 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).

Look at the molecule:
http://wsrv.clas.virginia.edu/~rjh9u/hemoglob.html
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You mnight be able to see it in 3-D here: http://cheetah.ma.iup.edu/courses/ls499/molecule/, and follow the path of Oxygen as it enters the blood stream and attaches to a heme molecule.

The basic backbone of the chain is straight, but there are side chains, very important for the molecule's functioning. And at the amino acid proline, the chain kinks.

When oxygen is inserted, the molecule changes to hold it securely. This made the great chemist Roald Hoffman think of the way a puck settles into the glove of a great hockey goalie. And when it is time for hemoglobin to give up the oxygen, it changes again. There is some iron in the center of the molecule, and oxygen attaches to the iron.

As we know, small changes make big differences. Carbon monoxide fits into that basket space too. Cyanide works by changing the heme structure so it cannot carry oxygen. An alteration of only ONE amino acid in the protein strand causes Sickle Cell Anemia. This disease lowers the amount of oxygen that can be carried, and slows bloods passage.

Accompany the investigators of Sickle Cell Anemia here, and see if you can follow their steps as they thought about the disease with the evidence available to them.
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