this is adult human hemoglobin it is responsible for the transport of oxygen throughout the body enabling all cells within the body to acquire oxygen from their environment it is present in the cytoplasm of red blood cells oxygen is needed in the body to act as the terminal electron acceptor in the electron transport chain through aerobic respiration this protein is made up of four subunits two alpha and two beta subunits each containing an essential iron heme prosthetic group in a pocket within the protein an important feature of hemoglobin is a cooperative binding of oxygen to each subunit due to the conformational changes upon oxygen binding to the heme iron it is a globular protein which is located in the aqueous cytoplasm of the cell in order to become soluble within the cytoplasm hemoglobin folds into a globular protein with hydrophilic amino acid side chains on the exterior of the protein and this the electron density surface of hemoglobin hydrophilic residues are blue this further illustrates how hemoglobin is able to exist within the cytoplasm of the cell this is adult human myoglobin which is structurally similar to the beta subunits of hemoglobin unlike human loeben where the functional structure is a hetero tetramer made up of four monomers the functional myoglobin unit is one Americ myoglobin is responsible for oxygen storage within muscle cells it is made up of one polypeptide and an iron bound heme group which is the portion of the protein responsible for binding the oxygen like hemoglobin myoglobin is a soluble called popular protein that exists in the cytoplasm of cells however my globin is located in muscle cells similarly to hemoglobin the myoglobin monomer folds so that the hydrophobic amino acids face the interior of the protein and the hydrophilic residues face the exterior in order to interact favorably with water in this the electron density surface of myoglobin hydrophilic residues are blue in both myoglobin and hemoglobin the iron center of the heme group carries out the important job of reversibly binding to oxygen the heme group itself is a large aromatic protoporphyrin ring the iron has a to plus oxidation state with six valence D electrons during reversible binding to oxygen the iron Center alternates between five and six coordinate species and alternates between high-spin iron 2 and low-spin iron to the four equatorial coordination sites arise from binding with the for aromatic nitrogen's within the protoporphyrin ring there's also an axial ligand for a histidine the midazolam which anchors the heme complex to the protein the last coordination site which may or may not be occupied is where oxygen reversibly binds when oxygen is bound to the iron 2 in the heme group it is 6 coordinate low-spin the geometry of the system is an octahedral and the charge transfer electron transitions within the system are what is responsible for the red color of oxygenated blood when hemas deoxygenated the iron remains in the 2 plus oxidation state but is 5 coordinate high-spin the geometry of the system is square pyramidal as it has 5 ligands the DTD energy transitions within this system result in the transmission of blue light explaining why deoxygenated blood is blue as oxygen binds to the iron within the heme group it changes the spin of the iron to go from high spin to low spin causing the iron to enter into the same plane as the protoporphyrin ring the movement of the iron into the plane of the Ring causes the histidine to be pulled towards the iron into the pocket of the protein in the case of hemoglobin the playing of this histidine results in the characteristic cooperative binding of oxygen among hemoglobins four subunits the movement of this histidine causes the hemoglobin protein to change confirmations depending upon whether oxygen is bound to the protein or not this change in conformation causes a change in the affinity of the other subunits of the protein for oxygen when the first oxygen binds to hemoglobin the slight structural shift that with dioxygen binding result in the increased oxygen affinity of the other three subunits allowing hemoglobin to more easily bind to the additional oxygen molecules you