Dissolution, hemoglobin binding, and the bicarbonate buffer system are ways in which carbon dioxide is transported throughout the body. Carbon dioxide molecules are transported in the blood from body tissues to the lungs by one of three methods:.
Several properties of carbon dioxide in the blood affect its transport. First, carbon dioxide is more soluble in blood than is oxygen. About 5 to 7 percent of all carbon dioxide is dissolved in the plasma. Second, carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin. This form transports about 10 percent of the carbon dioxide. When carbon dioxide binds to hemoglobin, a molecule called carbaminohemoglobin is formed.
Binding of carbon dioxide to hemoglobin is reversible. Therefore, when it reaches the lungs, the carbon dioxide can freely dissociate from the hemoglobin and be expelled from the body.
Third, the majority of carbon dioxide molecules 85 percent are carried as part of the bicarbonate buffer system. In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase CA within the red blood cells quickly converts the carbon dioxide into carbonic acid H 2 CO 3. Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood, down its concentration gradient. The newly-synthesized bicarbonate ion is transported out of the red blood cell into the liquid component of the blood in exchange for a chloride ion Cl- ; this is called the chloride shift.
When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion. This produces the carbonic acid intermediate, which is converted back into carbon dioxide through the enzymatic action of CA. The carbon dioxide produced is expelled through the lungs during exhalation.
This is important because it takes only a small change in the overall pH of the body for severe injury or death to result. The presence of this bicarbonate buffer system also allows for people to travel and live at high altitudes. When the partial pressure of oxygen and carbon dioxide change at high altitudes, the bicarbonate buffer system adjusts to regulate carbon dioxide while maintaining the correct pH in the body.
To learn more about Healthwise, visit Healthwise. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated. It looks like your browser does not have JavaScript enabled. Please turn on JavaScript and try again. It's a colourless, odourless, and tasteless gas that is lighter than air and can be fatal to life.
It has a greater affinity for hemoglobin than oxygen does. It displaces oxygen and quickly binds, so very little oxygen is transported through the body cells.
Does it have anything to do with the oxidation state of oxygen in each molecule? You might also look at the orbital pictures in this answer by Martin.
Copied from this site and first used in this answer of mine. Metal orbitals are 3d, 4s, 4p from bottom to top; ligand orbitals are of s-type.
You will notice that figure 1 contains the irreducible representations of the orbitals beneath them. Orbitals can only interact if they have identical irreducible representations; otherwise, their interactions will sum up to zero.
Further down in the internet scriptum I originally copied the picture from , you can see a set of two pictures that introduce p-orbitals.
Such is the case for the porphyrin-iron II system that forms the heart of haemoglobin: The central iron II ion is coordinated well from five directions four from the porphyrin ring and one histidine of haemoglobin and has a weakly bound water atom in the ground state in its sixth coordination slot, sometimes displaced by a distal histidine.
Carbon monoxide can diffuse in and bind very well to this system, displacing the weakly bound water and histidine. What happens here is rather complex, and the last lecture I heard on the topic basically said that final conclusive evidence has not yet been provided. Orthocresol discusses the different viewpoints in detail in this question. The diamagnetic properties of the resulting complex are, however, unquestioned and thus one must assume a singlet ground state or one where antiferromagnetic coupling cancels any spins at molecular levels.
Since the ground state of haemoglobin has a high-spin iron II centre and the ground state of oxygen is a paramagnetic triplet, it makes sense to assume those two to be the initial competitors. This induces a high-spin low-spin transition on iron and slightly reorganises the ligand sphere pulling oxygen closer to the iron centre.
We can attribute that electron to the iron centre. Content in the link I quoted from are in German; translation mine and shortened from the original. Only due to the complexly tuned ligand sphere and also due to the stabilising high-spin low-spin transition plus reorganising is oxygen able to bind to iron at all. The distal histidine further stabilises the complex by a hydrogen bond, alleviating the charge slightly.
It is to be assumed that nature did a great deal of tuning throughout the evolution since the entire process is rather complex and well-adjusted for collecting oxygen where it is plentiful in the lungs and liberating it in tissue where it is scarce. The simpler picture I drew above for carbon monoxide is not correct. This is because the entire binding pocket is made to allow oxygen to bind as I stated thus attempting everything to make oxygen a comfortable home.
But since carbon monoxide was so good and oxygen so poor to start with, the former still binds better than the latter. The answer has to do with pi-backbonding. In essence, the CO molecule has a negative formal charge on the carbon it's neutral because of the oxygen having a positive formal charge. However, C is quite electropositive, and would like to relieve the stress caused by the negative formal charge. To relieve the stress caused by the negative charge, the CO molecule will want to bond to the iron.
Note that the 4, 5, and 6 sigma orbitals, as well as the 2 pi orbital, are all antibonding. Carbon monoxide impedes the transport of oxygen in blood by competitive binding to the oxygen binding sites on hemoglobin. The affinity of these sites for carbon monoxide is much greater than that for oxygen.
Reported values differ between authors Douglas et al. However, this ratio is not a constant but depends on the level of saturation Roughton, as well as on pH Joels and Pugh, This means that simple procedures cannot be used to calculate the combined effects of simultaneous oxygen and carbon monoxide binding.
Application of our mathematical model of hemoglobin Zock, shows that this model can account for the above-mentioned phenomena in a straightforward way. Unable to display preview. Download preview PDF. Skip to main content. This service is more advanced with JavaScript available.
0コメント