oxygen is transported in blood in two ways:
dissolved in plasma (only 1.5% because O2 is poorly soluble in plasma)
bound to hemoglobin inside RBCs (98.5% is carried this way)
Hemoglobin
hemoglobin (Hb) is a protein composed of 4 polypeptide chain subunits
each subunit is bound to an iron-containing heme group
since iron ions serve as oxygen-binding sites, each hemoglobin can rapidly and reversibly bind 4 oxygen molecules
Hemoglobin II
a hemoglobin molecule bound with oxygen is called oxyhemoglobin (HbO2)
a hemoglobin molecule that has released its oxygen is called deoxyhemoglobin (HHb)
Hemoglobin and Oxygen Transport
when the first oxygen molecule binds the first iron molecule, the hemoglobin changes shape and the affinity for the other 3 oxygen molecules progressively increases
Hemoglobin and Oxygen Transport II
similarly, when the first oxygen is unloaded, the affinity for oxygen is decreased and it becomes progressively easier for the other 3 oxygen molecules to dissociate from the hemoglobin
Hemoglobin and Oxygen Transport III
hemoglobin is fully saturated when all four heme groups are bound to oxygen
if fewer than all four heme groups are bound, the hemoglobin is said to be partially saturated
