Question

Discuss the roles of hemoglobin and myoglobin in transporting oxygen and carbon dioxide, including process/strategy of oxygen uptake and release in the body, and location of molecule in the body.

Answer 1

Hemoglobin is an essential component of red blood cells that transport oxygen throughout the blood from the lungs to all tissues of the body.Hemoglobin also carries carbondioxide to the lungs to complete the process of respiration.Once the Hb-O₂ complex reaches the tissue that consumes oxygen ,the O₂ molecules are transferred to another protein myoglobin which transports oxygen through the muscle tissue. Myoglobin supplies oxygen to muscles only which is helpful at the starving time of oxygen.

Vertebrate hemoglobin is a spherical protein molecule consisting of an array of four globin polypeptide chains,each contain a heme group which is the oxygen binding site.Its molecular weight is approximately 64500 daltons. The oxygen uptake of hemoglobin exhibits cooperatively such that each oxygen successfully increase the affinity of the molecule for adding another oxygen up to four.The site at which oxygen binds to both hemoglobin and myoglobin is the heam. The cooperative interaction between different binding sites makes hemoglobin an unusual good oxygen transport because it enables the molecule to pickup as much oxygen as possible when the partial pressure of oxygen drops significantly below this threshold level.

The structure of myoglobin suggest that the oxygen carrying heme group is buried inside the protein portion of the molecule ,which keeps pair of heme groups from coming too close together.This is important because these proteins needs to bind oxygen reversabily and the Fe(II) heme by itself cannot do this.When there is no globin to protect the heme,it react with oxygen to form an oxidised Fe(III) atom instead of an Fe(II)-O₂ complex.

The changes that occur in the structure of hemoglobin when oxygen binds to the hemes are so large that crystals of deoxygenated hemoglobin shatter when exposed to oxygen.Further evidence for the flexibility of proteins can be obtained by noting that there is no path in the crystal structures of myoglobin and hemoglobin along which an oxygen molecule can travel to reach the heme group.The fact that these proteins reversibly bind oxygen suggests that they must undergo simple changes in their conformation changes that have been called breathing motions that open up and close down the pathway along which an oxygen molecule travels as it enters the protein.