hemoglobin is made up of globin proteins and an iron-rich compound known as heme it is found in red blood cells and is involved in the transport of oxygen around the body red blood cells do not have a nucleus increasing the amount of space for hemoglobin there are approximately 300 million hemoglobin molecules in each red blood cell the structure of hemoglobin enables it to carry oxygen with high efficiency it has a quaternary structure made up of four globin subunits most commonly - alpha and two beta subunits in the center of each globin subunits is a heme group which is where oxygen binding takes place each hemoglobin molecule can therefore bind with four molecules of oxygen one on each hand group oxygen binds to hemoglobin in their lungs where the concentration of oxygen is high binding of oxygen is a cooperative process this means that when an oxygen molecule binds to one of the heme groups it causes a conformational change in the protein which makes it easier for oxygen to bind to the other heme groups the cooperative binding process of hemoglobin is highlighted in the oxygen dissociation curve this graph shows the partial pressure of oxygen a way of measuring the concentration of oxygen on the x-axis and the percentage saturation of hemoglobin on the y-axis the graph is sigmoidal or s-shaped once oxygen has loaded onto hemoglobin it is transported by the red blood cells to tissues around the body and unloaded into cells which need oxygen for aspiration carbon dioxide in the tissues creates an acidic environment affecting the structure of hemoglobin and lowering its affinity for oxygen a small decrease in the pH results in a large decrease in the percentage saturation of oxygen the oxygen dissociation curve is affected by levels of carbon dioxide in the blood for example when carbon dioxide levels go up after exercising the presence of carbon dioxide helps the release of oxygen from hemoglobin so the curve shifts to the right this is known as the Bohr effect oxygen unloads from hemoglobin one molecule at a time and hemoglobin returns to its deoxyhemoglobin structure a developing fetus also needs oxygen from its mother's blood fetuses and young infants have a different type of hemoglobin from adults fetal hemoglobin has two alpha and to gamma globin chains and this structure enables it to bind oxygen with a greater affinity this means that the fetal hemoglobin will always load oxygen from the mothers hemoglobin hemoglobin is found in the red blood cells of most vertebrates and some invertebrates different organisms have different types of hemoglobin and their dissociation curves reflect this for example alarma living at high altitude where oxygen levels are reduced needs to be able to pick up oxygen even at low levels so the curve shifts to the left you