Hemoglobin from a molecular point of view.

Hemoglobin from a molecular point of view. As such, hemoglobin is the main structure responsible for gaseous exchange, from the alveoli to the tissues, to determine the molecular structure were developed various physical-chemical analyzes such as X-ray crystallography, among others. In general hemoglobin is a protein that consists of four polypeptide chains (a quaternary structure) 2 alpha chains and 2 beta chains called globins and linked together by sulfur-sulfur bridges. Recall our biochemical classes ... an amino acid is formed by an amino functional group (NH3) and a carboxylic acid group (COOH). When two amino acids are bound together they form peptides, when they are joined by peptide bonds, they form polypeptides and when they are considerably large, they have a stable and three-dimensional structure, we can call it protein. 


Now, each of these globin chains is joined by a "hemo" group, let's remember our organic classes again and analyze ...


 the "hemo" group consists of a protoporphyrin structure, now what is it ?, is nothing (Pyrrole groups are 4 carbon atoms heterocycles and 1 heteroatom "Nitrogen") these pyrrole groups are joined by methylene (R = CH 2) linkages. In the center of the protoporphyrin ring, there is an iron ion with oxidation state of +2, then broadly the hemoglobin is formed by a protein part (globine) and another non-protein (heme group), which in turn The form the porphyrin and an atom of iron. 

After this, if we analyze the structure in detail, conjugated double bonds can be observed and these are susceptible to the electromagnetic radiation, as they contain "pi" electrons, they can be excited going from a basal state to one of maximum energy and therefore can absorb Visible light at wavelengths of 540 nm (clear, in addition to the Soret band characteristic of porphyrins). For this reason we can measure the maximum absorbance and quantify the hemoglobin concentration in the blood in a spectrophotometer following Beer's law, in fact most of the automated equipment base the physical principle on this.