Biological complexity: how hemoglobin wolrks (Introduction)

by David Turell , Thursday, March 30, 2017, 01:56 (2796 days ago) @ David Turell

this amazing molecule carries oxygen to the tissues and takes back C02 to the lungs. At either end of the cycle the molecule easily releases its carried gas:

https://www.evolutionnews.org/2017/03/why-understanding-intelligent-design-helps-us-to-...

. Specifically, the hemoglobin molecule has an increased affinity for oxygen (O2) in the alveoli of the lung, where the O2 level is high. But it has a decreased affinity for O2 in the capillaries of the peripheral tissues, where the O2 is low and the high level of carbon dioxide (CO2) makes the tissues more acidic. (This is called the Bohr effect, after Danish physiologist Christian Bohr.) So hemoglobin releases O2 at precisely the point where it has the shortest path to diffuse from the blood to the mitochondria of the cells.

By a different mechanism, hemoglobin in the peripheral capillaries binds to CO2. This converts the molecule to carbaminohemoglobin, which has a low affinity for O2. In the alveolar capillaries of the lung, where the level of CO2 is low and the level of O2 is high, carbaminohemoglobin releases its CO2 and reverts to hemoglobin, with its high affinity for O2. (This is called the Haldane effect, after Scottish physiologist John Haldane.)

We are able to plot an Oxyhemoglobin Saturation curve comparing the degree of oxygen saturation of hemoglobin to the level of oxygen in the blood. Under conditions in the lung represented by the green curve (high O2, low CO2) hemoglobin takes up oxygen more readily; under conditions represented by the red curve in the peripheral tissues (low O2, high CO2), hemoglobin takes up oxygen less readily.

Comment: This is a very large molecule with very special properties. It has a cousin in the muscles of the body where extra oxygen is stored for use. It is called myoglobin and looks a lot like hemoglobin. This arrangement cannot be the result of a chance process. The size of the molecule in terms of the number of amino acids is shown here:

https://www.google.com/?gws_rd=ssl#q=hemoglobin+molecule+size&*&spf=569

"Protein Structure. The hemoglobin molecule is made up of four polypeptide chains: two alpha chains < >of 141 amino acid residues each and two beta chains < > of 146 amino acid residues each. The alpha and beta chains have different sequences of amino acids, but fold up to form similar three-dimensional structures." That is 574 smino acids in a precise structure to make it act as it does.

If anything shows design, this does!