Hemoglobin is the most important element inside a red blood cell. It is a hemoprotein with the ability to transport oxygen, with the structure of a tetramer. Each molecule consists of four monomers, with loose bonds connecting them. The name comes from the components, since there are two globins, which are pairs of polypeptide chains, with a hemme molecule on each one of them. The hemme molecule is made of protoporphyrin with a large amount of iron.
The main role of this critical blood protein is to carry oxygen produced in our lungs to every single part of the body. Hemoglobin is also responsible for the distinctive red color of blood. When the cells are loaded with oxygen, the blood has a richer red color when compared to depleted blood that travels back to the lungs. Hemoglobin is constantly lost and the bone marrow always produces new amounts in order to replace it.
The mechanism of hemoglobin production and action is very complex and controlled by genetic coding. Mothers supply their own oxygenated blood to babies in the womb, which allows them to feed their tissues without actual respiration. To make this possible, hemoglobin is produced by the combination of two separate compounds, named hemoglobin alpha and hemoglobin gamma, along with an atom of iron and several of nitrogen. After birth, hemoglobin gamma is replaced by a different compound named hemoglobin beta but the rest of the process remains the same.
This essential protein has the ability to attract molecules of oxygen. This is due to the iron atom in its composition, which binds with any available oxygen as the blood travels through lungs. The blood will then flow and reach all parts of the body, supplying oxygen to internal organs, tissues or cells. Red blood cells need to be replenished constantly. Old and damaged cells are sent to the digestive system for recycling while new ones take over their duties.
However, there are many problems that can appear in the process of transporting oxygen from lungs to cells. Sickle cell anemia for example is a serious disease with genetic roots that causes alpha or beta hemoglobin to have a wrong shape. If one of them is sickle-shaped, which also gives the name of this condition, the two proteins can't bond properly.
In general, the term anemia implies that there isn't enough iron in the red blood cells, for various reasons. If hemoglobin lacks the atom of iron in its composition, it can't attract oxygen from the lungs, or does it very poorly. The effects become more and more severe in time and eventually cripple the entire body.
Several serious conditions, for example cancer or diabetes, can affect hemoglobin and blood composition in general. This is why hemoglobin levels are commonly measured in standard blood tests. The level of sugar in the blood stream is a more relevant test for diabetes, since it is directly influenced by this metabolic disease.
A well-known flaw of hemoglobin is that it can attract other gases instead of oxygen. It is 200 times more likely to bind with carbon monoxide for example, which is the reason why this gas is so dangerous. Carbon monoxide is produced by car exhausts among other sources and this toxin can reach our lungs instead of oxygen. As a result, hemoglobin transports a lower amount of oxygen to cells, a form of slow asphyxiation. Carbon monoxide is also found in cigarettes and smokers actually supply 20% less oxygen to their tissues than people who don't smoke.
In some cases, the fact that hemoglobin is attracted to other gases can be very useful. For example, anesthesia is based on the attraction between hemoglobin and the gases used in the procedure. The protein carries the anesthetic gas, for example nitrous oxide, to the brain. This effect can be controlled so that the patient is sedated as much as needed. Supplying oxygen to the lungs again cancels this effect, as the gases used as anesthetics become waste and are eliminated from the body.
Low levels of hemoglobin are popularly known as anemia, a term that also designates a low number of red blood cells. Of course, if the number of cells is lower than normal, this will be reflected in the total amount of hemoglobin.
There can be many causes for this condition. One of the most common is the direct loss of blood, due to various causes. These include surgery, wounds but also internal bleeding or diseases like stomach ulcer or some forms of cancer. If the bone marrow is affected, by cancer for example, it simply can't produce enough hemoglobin. Sickle cell anemia, thalassemia or other conditions related to an unusual structure of hemoglobin also lead to anemia. Kidney failure is another cause, as well as aggressive treatments like chemotherapy that inhibit the production of red blood cells. Finally, a common cause for anemia is improper nutrition, especially a diet poor in iron, folate or vitamin B12.
It is also possible to have a level of hemoglobin that is higher than normal. This is typical of smokers and people who live at high elevations but it can also be an effect of dehydration. It is just temporary in this case and the level drops back to normal after enough fluids are supplied.
Other causes are also possible but are quite uncommon. It can be a sign of doping, since some athletes try to artificially increase their blood cells count in order to boost the amount of available oxygen. Several banned substances can have this effect, especially erythropoietin. Some diseases can also increase hemoglobin levels, in particular polycythemia rubra vera, which is a bone marrow problem, some types of cancer as well as emphysema and other severe lung disorders.
Hemoglobin is a so-called tetramer molecule. It consists of two protein chains named globins, with the alpha globin being a chain of 141 amino acids, while there are 146 amino acids in the beta globin chain. There are 8 helical segments in the secondary and tertiary structures of both chains, which are identical. One hemme molecule is present in each chain and includes a ion of iron in the center, with four molecules of pyrrole linked to form a porphyrin ring. Globin chains are subdivided in two dimmers, with a very strong connection between them. The location of the critical hemme molecule is inside the globin protein, between the helixes E and F.
The main role of hemoglobin is to transport oxygen. Working with some other chemical compounds, the molecules take oxygen atoms from the lungs and ferry them to all parts of the body. An interesting effect is that the level of oxygen is actually the regulator of hemoglobin's affinity for this gas. If a lot of oxygen is present inside the lungs, hemoglobin becomes more attracted to it and transports increased amounts. If oxygen levels are low, the attraction also decreases. Even when oxyhemoglobin is saturated and the maximum level of oxygen has already been loaded, it still increases the attraction for this gas.
Scientists have named this effect cooperativity. It is considered to be very important in our metabolism, since it helps the transport of the maximum amount of oxygen to tissues and cells. In addition, it regulates the activity of deoxyhemoglobin. Some chemical factors that play a role in this process have been identified, these include the common carbon dioxide and also pH and DPG (2, 3-diphosphoglycerate).
Besides oxygen, hemoglobin can also carry some carbon dioxide, which is a by-product of our metabolism, back to the lungs. However, this is a secondary role and most carbon dioxide is ferried by the blood plasma.