H.6.2+HA

haemoglobin is: -an oxygen-carrying pigment made up mainly of proteins -it has 4 hemes so 4 oxygens can attach to it -at moderate partial pressures haemoglobin releases oxygen

myoglobin is: -also oxygen-carrying pigment -it has 1 heme group and so 1 oxygen attaches to it -releases oxygen when partial pressure of oxygen is low - therefore acts as an oxygen store, allowing muscle fibres to continue aerobic respiration for longer

The percentage saturation of haemoglobin with oxygen (i.e. how many haemoglobins have oxygen attached-they can only have either 0 or 4 oxygens) at each partial pressure of oxygen is shown on an oxygen dissociation curve.

The myoglobin oxygen dissociation curve is further left than that of haemoglobin

This is how myoglobin shifts the curve:



The fetal haemoglobin curve is farther left than that of adult haemoglobin. This is because fetal haemoglobin has a greater affinity for oxygen than adult haemoglobin. This allows for oxygen that dissociates from adult haemoglobin in the placenta to be quickly picked up and bound to the fetal haemoglobin. This oxygen is then carried to the tissues of the fetus, to allow for its cellular respiration.

__In other words:__ An oxygen dissociation curve shows that percentage saturation of hemoglobin with oxygen at each partial pressure of oxygen. The oxygen curve for myoglobin is to the left of the curve for adult hemoglobin because myoglobin has a higher affinity for oxygen.

The dissociation curves for myoglobin and hemoglobin contrast in their shape. The curve for hemoglobin is S-shaped while that for myoglobin is not. Hemoglobin has four heme groups, each of which is attached to different globins that interact with each other. Myoglobin, on the other hand, only consists of one heme group attached to a globin. As the oxygen molecules dissociate from hemoglobin, a structural change occurs which makes it easier for other oxygen molecules to dissociate. Blood with adult hemoglobin releases large amounts of oxygen over a narrow range of oxygen partial pressures.

Fetal hemoglobin is structurally different from normal hemoglobin. The fetal dissociation curve for myoglobin is shifted to the left relative to the curve for the normal adult. Typically, fetal oxygen pressures are low, and hence the leftward shift enhances the placental uptake of oxygen.