Role of Hemoglobin at the Molecular Level - Essay Example

To understand the transportation of oxygen and carbon dioxide at a molecular level, it is important to understand the structure of Hemoglobin (Figure).  A heme group consists of an iron (Fe) ion (charged atom) held in a heterocyclic ring, known as a porphyrin. As seen from the figure the iron ion is the site of oxygen binding and bonds with the four nitrogens in the center of the ring. The iron is also bound strongly to the globular protein. A sixth position can reversibly bind oxygen, completing the octahedral group of six ligands. Oxygen binds in an "end-on bent" geometry where one oxygen atom binds Fe and the other protrudes at an angle. When oxygen is not bound, a very weakly bonded water molecule fills the site, forming a distorted octahedron.

Oxyhemoglobin is formed during respiration when oxygen binds to the heme component of the protein hemoglobin in red blood cells and occurs in the pulmonary capillaries near the alveoli of the lungs. The oxygen then travels through the bloodstream to all the tissues and cells where it is utilized in aerobic glycolysis and the production of ATP by the process of oxidative phosphorylation. Deoxyhemoglobin is the form of hemoglobin without bound oxygen (Wikipedia, 2007).

The following are the important reactions that occur:

1. Involving oxygen

Hemoglobin bonds with oxygen according to the following reaction:

            Hb                +        O2    ----->      HbO2            

2. Carbon Dioxide

Bicarbonate ions react with the Hydrogen ions that are released from reduced hemoglobin and are in turn converted to water and carbon dioxide. For this reaction to occur an enzyme called Carbonic Anhydrase is required as a catalyst. The end product of the reaction is water and carbon dioxide which are then exhaled.                                                     

                                                         carbonic
                                                         anhydrase
   HCO3-             +          H+                 ----->       H2CO3       ----->           CO2 (exhaled)     +                  H2O (exhaled)

3. Hemoglobin

Hemoglobin carrying Hydrogen ions is called reduced hemoglobin. Hemoglobin releases the Hydrogen ions it is carrying.

          HHb                        ----->           Hb       +                   H+

Hemoglobin carrying Carbon Dioxide is called carbaminohaemoglobin. Hemoglobin releases the Carbon Dioxide it is carrying according to the following reaction:

               HbCO2                    -------->         Hb                  +               CO2 (exhaled)

(abbysenior.com, N.D.)

To put it in simple terms hemoglobin can bind oxygen and carbon dioxide. The amount of oxygen bound to hemoglobin is determined by oxygen concentration, carbon dioxide concentration, and pH. In general, the following seven steps occur:

1. Hemoglobin in RBCs entering the lungs has carbon dioxide bound to it.
2. In the lungs, the oxygen concentration is high and carbon dioxide concentration is low due to breathing.
3. Due to this variation of concentration the hemoglobin binds oxygen and releases carbon dioxide.
4. The oxygen-bound hemoglobin then gets transported through the heart and blood vessels to the muscle.
5. In muscle, the carbon dioxide concentration is high and the oxygen concentration is low due to metabolism.
6. At this point, hemoglobin releases oxygen and binds carbon dioxide.
7. Hemoglobin together with the CO2 gets transported back to the lungs and the cycle repeats (Freudenrich, 2007).

Relationship between oxygen and hemoglobin in hot working muscle

Our skeletal muscle burns both carbohydrates and fat for producing energy and is capable of functioning with or without oxygen. However, it is noticed that in the absence of oxygen, metabolism produces lactic acid and consumes glucose stores. When a muscle works under anaerobic conditions, it produces lactic acid and is highly inefficient. And this is the reason for the feeling of fatigue. When the oxygen supply is scarce, only glucose can be used to produce energy and it can quickly get depleted. Muscles have adapted to this frequent imbalance between energy demand and supply by switching between fat and carbohydrate metabolism, based on oxygen availability.

Initially, when a person starts to do some exercise, muscles generally work anaerobically and produce lactic acid until the blood rich in oxygen is carried to the muscles and supplies enough oxygen. Further, as exercise continues at a steady pace, the muscle begins to utilize more fat as fuel for energy. If a person continues the exercise, the muscles cannot get adequate oxygen and go back to the anaerobic metabolism. The lactic acid produced by anaerobic metabolism eventually blocks the metabolism and the muscles develop severe spasms, felt as cramps. However, if enough oxygen is available, glucose is metabolized to carbon dioxide. Muscle fatigue occurs when the glucose stores are consumed and the muscle needs to work in an anaerobic condition (Bove, N.D.). This is what happens in hot working muscles. For example, athletes burn up more calories than non-athletes and hence they require food that gives enough energy to help their muscles. Therefore, it can be said that hemoglobin is important for good health. To increase the iron content which determines the oxygen-carrying capacity of the blood, an individual needs to consume iron-rich food such as a good amount of green leafy vegetables.  A well-balanced diet can keep each one of us healthy.