Why is hemoglobin red?

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The human blood consists of red blood corpuscles, or RBCs, along with other types of blood cells. The higher the number of RBCs which constitute the blood vessels, they will give the color to the blood. As there are trillions of RBCs that are present circulating in the human body, their higher number keeps the hemoglobin content also higher in the blood. Hemoglobin is the red-colored pigment and imparts the red color to the blood. This molecule is found to be comprised of protein and iron.

The hemoglobin is the molecule that resides in the RBCs, and it carries oxygen in the blood. The term “hemoglobin” originates from two words called “globin” and “heme.” The hemoglobin constitutes the subunits of globin protein with a group called heme embedded into it. The heme part of the hemoglobin molecule consists of an iron atom which is involved in oxygen binding. The capacity of hemoglobin is to carry oxygen. The non-protein group that constitutes the hemoglobin is “heme.” This group is known to be comprised of an organic ring which surrounds the iron atom.

The porphyrin ring is built by porphyrins also called a tetrapyrrole ring. This ring consists of numerous double bonds of conjugated types that make the porphyrins to absorb the light in the visible region of the spectrum. The iron atom, which is attached to the protein chain, will alter the absorption wavelength, and it provides the hemoglobin its red color which is considered to be characteristic of the molecule.

The hemoglobin that exists along with oxygen as present in the arteries is red in color. The hemoglobin that is devoid of oxygen will get converted into a dark red color. The blood in the vein and the veins that are observed far inside the skin appears a blue color. This is because of the blue light reflection from the venous tissues.

Author: Hari M

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