Case 4- carrying O2 and CO2 Flashcards
Structure of Haemoglobin
Haemoglobin is a complex protein with a quaternary structure, it is made of 4 polypeptide chains. In Haemoglobin A1: 2 are alpha and 2 are beta, in Haemoglobin A2: 2 are alpha and 2 are delta, in foetal Haemoglobin: two are alpha and two are gamma. Most Haemoglobin is the type A1. Within each polypeptide chain there is a haem group which contains an Iron atom.
Dalton’s law
In areas of low 02 partial pressure there will be a low affinity. This means that oxygen will be released in tissues which are oxygen deficient
Change in the structure of haemoglobin as it bonds to oxygen
Within the alpha helix you have a histidine protein which is bonded to iron, this is in its tense state. When the oxygen bonds with the Iron it causes a shift to the relaxed state. It changes the shape of the other sub units so its easier for oxygen to bond with the other haem groups. The alpha helix refers to the secondary structure of a molecule and not the alpha polypeptide.
The Haemoglobin-oxygen dissociation curve
A sigmoid shape which plateaus at the top. Haemoglobin saturation increases as the partial pressure of oxygen increases
How increased temperature, decreased pH and increased 2-3 DPG affects the haemoglobin-oxygen dissociation curve
The curve goes to the right as these factors decrease the affinity of haemoglobin for O2 which increased O2 release. These factors are normally present with increased exercise which means the cells would require more oxygen, which is why more is being released
What is 2-3 DPG
A product of respiration
How decreased temperature, increased pH and decreased 2-3 DPG affects the haemoglobin-oxygen dissociation curve
The graph shifts to the left as the haemoglobin increases its affinity for oxygen. The pH is higher because there is less CO2 in the blood in the blood from metabolicaly active tissue
Why the shift in curve is important
Important for metabolically active tissue, so areas which have higher oxygen need get it as they generate heat and a lower pH (release of Co2) and more 2-3DPG is released.
The Bohr effect
The lower pH changes haemoglobin conformation as the hydrogen binds to the Hb and O2 dissociates.
Link between CO2 and H+- case 4
When there is more CO2 it can bond to the haemoglobin, the O2 disasociates and H+ ions are generated
How 2-3 DPG affects oxygen affinity
2-3 diphospgoglycerate is a metabolite of glycolysis and interacts with the amino acids on the beta chain, this destabilises the interaction of haemoglobin with O2. In hypoxia there is low PO2 in the tissues, so there is more glycolysis and more 2-3DPG release causing more O2 to be released which counters hypoxia.
The three ways carbon dioxide are carried in the blood stream
- Dissolved in plasma as CO2- more common in vein then arteries
- Bicarbonate- most is transported this way. More common in arteries then veins
- Bound to haemoglobin (carbamino haemoglobin)- More common in veins then arteries as less oxygen is being picked up by the haemoglobin.
What happens when CO2 binds with haemoglobin
CO2 dissolves through the endothelial capillary walls and enters the red blood cells. In binds to the NH2 group on the hameoglobin to form carbaminohaemoglobin and H+
How CO2 interacts with bicarbonate to be carried in the blood
CO2 dissolves through the endothelial capillary walls and enters the red blood cell. The CO2 combines with water using the enzyme carbonic anhydrase to form H+ and HCO3- (bicarbonate). The haemoglobin has a higher affinity for hydrogen then oxygen. So the oxygen disasociates from the haemoglobin and the hydrogen joins instead. The oxygen is then taken up by the cells. So high levels of CO2 leads to increased O2 dissociation
Chloride shift in red blood cell after CO2 reacts with water
After CO2 reacts with water an increased number of HCO3- ions diffuse out of the cell down the gradient. There is now an electrical imbalance as there are lots of negative ions outside the cell so more Cl- ions enter the cell down the gradient in order to equilibrate.
