THE AMAZING HEMOGLOBIN MOLECULE---A MIRACLE OF DESIGN

“Breathing seems so simple, yet it appears as if this elementary manifestation of life owes its existence to the interplay of many kinds of atoms in a giant molecule of vast complexity.”—Max F. Perutz, a sharer of the Nobel Prize in 1962 for his studies of the hemoglobin molecule.

BREATHING—what could be more natural? Most of us rarely give it a thought. Breathing, however, could not keep us alive if it were not for the human hemoglobin molecule, a complex molecular masterpiece designed by our Creator. The hemoglobin that is inside each of our 30 trillion red blood cells transports the oxygen from the lungs to the tissues throughout the body. Without hemoglobin, we would die almost instantly.

How do hemoglobin molecules manage to pick up tiny oxygen molecules at the right time, hold them safely until the right time, and release them at the right time? Several amazing feats of molecular engineering are required.

Tiny Molecular “Taxis”

You might think of each hemoglobin molecule in a cell as a tiny four-door taxi, with room for exactly four “passengers.” This molecular taxi does not require a driver, since it is riding inside a red blood cell, which could be described as a traveling container full of these hemoglobin molecules.

The journey for a hemoglobin molecule begins when red blood cells arrive at the alveoli of the lungs—the “airport.” As we inhale air into our lungs, the huge crowds of tiny recently arrived oxygen molecules start looking for a ride in a taxi. These molecules quickly diffuse into red blood cells, the “containers.” At this point, the doors of the hemoglobin taxis within each cell are closed. However, it does not take long before a determined oxygen molecule in the bustling crowd squeezes in and takes a seat in a hemoglobin taxi.

Now something very interesting happens. Inside the red cell, the hemoglobin molecule begins to change its shape. All four “doors” of the hemoglobin taxi begin to open automatically as the first passengers get in, which allows the remaining passengers to hop aboard more easily. This process, called cooperativity, is so efficient that in the time it takes to draw a single breath, 95 percent of the “seats” in all the taxis in a red blood cell are taken. Together the more than one quarter of a billion hemoglobin molecules in a single red blood cell can carry about a billion oxygen molecules! Soon the red blood cell containing all these taxis is off to deliver its precious supply of oxygen to body tissues that need it. But, you might wonder, ‘What keeps oxygen atoms inside the cell from getting out prematurely?’

The answer is that inside each hemoglobin molecule, oxygen molecules attach to waiting atoms of iron. You have probably seen what happens when oxygen and iron get together in the presence of water. The result is usually iron oxide, rust. When iron rusts, the oxygen is locked up permanently in a crystal. So how does the hemoglobin molecule manage to combine and uncombine iron and oxygen in the watery environment of the red blood cell without producing rust?

Taking a Closer Look

To answer that question, let us take a closer look at the hemoglobin molecule. It is made up of some 10,000 atoms of hydrogen, carbon, nitrogen, sulfur, and oxygen that are carefully assembled around just 4 atoms of iron. Why do four iron atoms need so much support?

First, the four iron atoms are electrically charged and must be carefully controlled. Charged atoms, which are called ions, can do a lot of damage inside cells if they get loose. So each of the four iron ions is secured in the middle of a protective rigid plate. Next, the four plates are carefully fitted into the hemoglobin molecule in such a way that oxygen molecules can get to the iron ions but water molecules cannot get to them. Without water, rust crystals are unable to form.

By itself the iron in the hemoglobin molecule cannot bind and unbind oxygen. Yet, without the four charged iron atoms, the rest of the hemoglobin molecule would be useless. Only when these iron ions are perfectly fitted into the hemoglobin molecule can the transport of oxygen through the bloodstream occur.

Releasing the Oxygen

As a red blood cell leaves the arteries and moves into the tiny capillaries deep in the body tissues, the environment around the red blood cell changes. Now the environment is warmer than in the lungs, and there is less oxygen and more acidity from the carbon dioxide surrounding the cell. These signals tell the hemoglobin molecules, or taxis, inside the cell that it is time to release their precious passengers, oxygen.

When the oxygen molecules get out of the hemoglobin molecule, it changes its shape once more. The change is just enough to “close the doors” and leave the oxygen outside, where it is most needed. Having the doors shut also prevents the hemoglobin from transporting any stray oxygen on the way back to the lungs. Instead, it readily picks up carbon dioxide for the return trip.

Soon the deoxygenated red blood cells are back in the lungs, where the hemoglobin molecules will release the carbon dioxide and be recharged with life-sustaining oxygen—a process that is repeated many thousands of times during a red blood cell’s life span of about 120 days.

Clearly, hemoglobin is no ordinary molecule. It is, as stated at the beginning of this article, “a giant molecule of vast complexity.” Surely, we are awed and thankful to our Creator for the brilliant and meticulous microengineering that makes life possible!

[Footnote]

This plate is a separate molecule called heme. It is not made of protein but is incorporated into the protein structure of hemoglobin.

 

TAKE GOOD CARE OF YOUR HEMOGLOBIN!

  “Iron poor blood,” an expression common in some places, is really hemoglobin-poor blood. Without the four essential iron atoms in a hemoglobin molecule, the other 10,000 atoms in the molecule are useless. So, it is important to get enough iron by eating a healthful diet. Some good sources of iron are listed in the accompanying chart.

  Besides consuming foods rich in iron, we should heed the following advice: 1. Get regular and appropriate exercise. 2. Do not smoke. 3. Avoid secondhand smoke. Why are cigarette and other forms of tobacco smoke so dangerous?

  It is because such smoke is loaded with carbon monoxide, the same poison emitted as exhaust by automobiles. Carbon monoxide is the cause of accidental deaths and is also a means by which some people commit suicide. Carbon monoxide binds to iron atoms in hemoglobin over 200 times more readily than oxygen does. So cigarette smoke quickly affects a person adversely by crowding out his intake of oxygen.

[Chart]

THE FOOD               PORTION SIZE               IRON(mg)

Blackstrap molasses    1 tablespoon               5.0

Raw tofu                         1/2 cup                    4.0

Lentils                             1/2 cup                    3.3

Beef chuck                    3 ounces                   3.2

Dried peaches                5 halves                   2.6

Kidney beans                  1/2 cup                    2.6

Wheat germ              1 ounce (1/4 cup)          2.6

Chickpeas                       1/2 cup                    2.4

Broccoli                      1 medium stalk             2.1

Dark meat turkey           3 ounces                   2.0

Spinach                         1 cup raw                  0.8

 

Heme

In the oxygen-rich environment of the lungs, an oxygen molecule will bind to the hemoglobin

After the first oxygen molecule binds, a slight change in the shape of hemoglobin allows three more oxygen molecules to bind rapidly

Hemoglobin transports the oxygen molecules away from the lungs and then releases them where they are needed in the body

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