Oxygen Dissociation Curves Flashcards
What is the structure of a haemoglobin molecule
Each haemoglobin molecule is a large globular protein made up of 4 polypeptide chains each with an iron-containing prosthetic group which can pick up 4 molecules of oxygen in a reversible reaction to form oxyhemoglobin.
How quickly do the oxygen molecules bind to the haemoglobin
The first oxygen molecule that binds to the haemoglobin alters the arrangement of the molecule making it easier for the following oxygen molecules to bind. The final oxygen molecule binds several hundred times faster than the first. The same process happens in reverse when oxygen dissociates from haemoglobin.
What is the concentration of oxygen like in red blood cells in the lungs
The concentration of oxygen in red blood cells when the blood enters the lungs is relatively low. Oxygen moves into the red blood cells from the air in the lungs by diffusion. Because the oxygen is picked up and bound to the haemoglobin the free oxygen concentration in the cytoplasm of the red blood cells stays low. This maintains a steep concentration gradient from the air in the lungs to the red blood cells so more and more oxygen diffuses in and is loaded onto the haemoglobin
What is the concentration of oxygen like in the body tissues
In the body tissues the oxygen levels are relatively low. The conc of oxygen in the cytoplasm of the red blood cells is higher than in the surrounding tissue. As a result oxygen moves out into the body cells by diffusion down its conc gradient. The haemoglobin molecules give up some of their oxygen. When you are at rest or exercising gently only 25% of the oxygen carried by the haemoglobin is released into your cells. There is another 75% reserve in the transport system for when you are very active.
What result does the strong affinity of haemoglobin for oxygen have
A small change in the proportion of oxygen in the surrounding air can have a big effect on the saturation of the blood with oxygen. So in the lungs the haemoglobin loads up rapidly with oxygen and in the tissues as the oxygen saturation of the environment falls oxygen is released rapidly as well
What is the Bohr effect
The Bohr effect is when the partial pressure of carbon dioxide is high the affinity of haemoglobin for oxygen is reduced. So haemoglobin needs higher levels of oxygen to become saturated and it gives up oxygen more easily. So in active tissues with high carbon dioxide levels haemoglobin releases oxygen very readily. Carbon dioxide levels in the lung capillaries are relatively low which makes it easier for oxygen to bind to the haemoglobin.
What is the function of fetal haemoglobin
Fetal haemoglobin is only found in the developing fetus. When it is in the uterus it is dependent on its mother to supply it with oxygen. Oxygenated blood from the mother runs through the placenta close to the deoxygenated fetal blood. If the blood of the fetus had the same affinity for oxygen as the blood of the mother very little oxygen would be transferred. But fetal haemoglobin has a higher affinity for oxygen and so can remove oxygen from the maternal blood. There is also a counter current exchange system.
What is the function of myoglobin
Myoglobin is a respiratory pigment found in the muscle tissue of vertebrates. It is a small bright red protein and has a similar structure to a single haemoglobin chain containing a haem group which binds oxygen. Myoglobin has a much higher affinity for oxygen than haemoglobin so it easily becomes saturated with oxygen and this affinity is not affected by the partial pressure of oxygen in the tissues. Once myoglobin is bound to an oxygen molecule it doesn’t give it up easily and so acts as an oxygen store. When oxygen levels in very active muscle tissue get really low and the CO2 levels are correspondingly high then myoglobin releases its store of oxygen when it is most needed.
