Lesson 9 - Transport of Oxygen and Carbon dioxide in the blood Flashcards
Erthyroctyes
Red blood cells
Adaptations of Erythrocytes:
- Biconcave shape
- No nuclei
Effects of biconcave structure
- Large surface area for diffusion of gases
- Helps pass through narrow capillaries
Where are RBCs formed?
Red bone marrow
Effects of no nuclei of RBCs?
- Limits lifetime
- More haemoglobin fits into cells
Haemoglobin:
Red pigment that carries oxygen and gives RBCs colour
Structure of haemoglobin?
- Large globular conjugated protein
- Quaternary structure
- 4 polypeptide chains. Each has an iron containing haem prosthetic group
Reaction between oxygen + haemoglobin and oxyhaemoglobin
Reversible reaction
Hb + 4O2 –> Hb(O2)4
Name for process:
- Oxygen binds to haem group
- Molecule changes shape
- Easier for the next oxygen to bind
Positive cooperativity
Definition of haemoglobin
A group of chemically similar molecules found in a wide variety of organisms. Protein molecules with a quaternary structure that has evolved to make it efficient at loading oxygen under one set of conditions but unloading it under a different set of conditions. It has four polypeptide chains which are linked together – each polypeptide is associated with a haem group which contains a ferrous (Fe2+) ion which can combine with an oxygen molecule (O2).
Loading oxygen
The process by which haemoglobin binds with oxygen. Associating.
In humans this takes place in the lungs.
Oxygen unloading:
Process by which haemoglobin releases oxygen. Dissociation.
Occurs in humans in tissues
High affinity:
Haemoglobins with this for oxygen take up oxygen more easily but release it less easily.
Low affinity:
Haemoglobin with this for oxygen takes up oxygen less easily but releases it more easily.
Oxygen dissociation curve:
The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen. Shows how at low oxygen concentrations little oxygen binds to haemoglobin (shallow gradient initially). After the first oxygen molecule binding the quaternary structure of the haemoglobin molecule changes, making it easier for the other subunits to bind an oxygen molecule, therefore it takes a smaller increase in the partial pressure of oxygen to bind the second molecule and third molecule so the gradient steepens. After the binding of the third molecule, it is less likely that a single oxygen molecule will find an empty site to bind to so the gradient of the curve reduces and the graph flattens off.
Positive cooperativity
Binding of the first molecule makes binding of the second easier and so on, so the gradient of the curve steepens.
Partial pressure
A measure of the concentration of a gas in a mixture of gases by calculating the pressure it contributes to the overall pressure.
Bohr shift
The greater the concentration of carbon dioxide the more readily the haemoglobin releases its oxygen because the more carbon dioxide there is, the lower the pH, the greater the haemoglobin shape change, the more readily oxygen is unloaded, the more oxygen is available for respiration.
How many oxygen molecules can bind to one haemoglobin molecule?
4
One oxygen molecule (O2) binds to one Fe2+ molecule.
Conditions that effect haemoglobin’s affinity for oxygen?
- Partial pressure of oxygen (pO2)
- Haemoglobin saturation
- Partial pressure of carbon dioxide (pCO2)
High affinity –>
high pO2
low pCO2
How does pCO2 effect haemoglobin’s affinity for oxygen?
CO2 leads to reduction in pH of blood. Water and CO2 react to form carbonic acid.
Low pH causes the tertiary structure of haemoglobin to be altered, decreasing affinity for oxygen. This is known as the bohr effect.
Bohr shift
Left -> pH increases
Right -> pH decreases
Haemoglobin of foetus in the womb?
Higher affinity.
Low oxygen –> shift to the left
Why does foetus haemoglobin have a high affinity to oxygen?
A different structure gives foetal haemoglobin a greater affinity to oxygen than adult haemoglobin. Oxygen binds to foetal haemoglobin more easily and is more reluctant to dissociate. This is important, as foetal haemoglobin needs to “steal” oxygen away from the mother’s haemoglobin when they pass in the placenta. If the foetal and maternal haemoglobin had the same affinity for oxygen, there would be no incentive for the oxygen to switch from the maternal blood to foetal blood.
Low oxygen environments examples:
- High altitude
- Live in sand or sea bed
Animals living in low oxygen environment haemoglobin?
High affinity
Low oxygen –> left
Smaller organisms with high SA:V
lower affinity
High respiration –> right
Organisms with high metabolic rate
lower affinity
High respirations –> shift to right
Higher metabolic rate explanation
Higher metabolic rate = more respiration = greater oxygen demand. This means the organisms need haemoglobin with a lower affinity for oxygen as they need it to easily unload oxygen to meet their high oxygen demand and allow a faster respiration rate.
Larger SA:V explanation
Small mammals that have a higher SA:V than larger mammals will lose heat more quickly so they have a higher metabolic rate to help maintain their body temperature. Other high activity organisms will also have a higher metabolic rate.
Means of transporting carbon dioxide:
- 5% dissolved in plasma
- Carbaminohaemoglobin
- Hydrogen carbonate ions in cytoplasm of red blood cells
Carbaminohaemoglobin:
CO2 is combined with amino groups in the polypeptide chains of haemoglobin to form a compound.
Hydrogen carbonate ions
HCO3^-
Reaction of CO2 and water to carbonic acid to hydrogen and hydrogen carbonate ions
CO2 + H2O <–> H2CO3 <–> H+ + HCO3-
How does reaction of carbon dioxide and water occur in blood plasma?
Slowly
How does reaction of carbon dioxide and water occur in the red blood cells?
High levels of enzyme carbonic anhydrase.
Chloride shift
Negatively charged hydrogen carbonate ions move out of erythrocytes into the plasma by diffusion down a concentration gradient. Negatively charged chloride ions move into the erythrocytes, which maintains the electrical balance of the cell.
Why is CO2 converted into HCO3- ions.
Maintain steep concentration gradient of CO2 to diffuse from the respiring tissue into the erythrocytes.
When there is a relatively low CO2 concentration?
Hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to form carbonic acid.
Chloride ions diffuse out of the RBCs back into the plasma down the electrochemical gradient.
Haemoglobins role in the chloride shift
- Acts as a buffer
- Prevents change in pH by accepting free hydrogen ions in a reversable reaction to form haemoglobinic acid
Haemoglobinic acid
Hydrogen ions + haemoglobin
