3B - Haemoglobin Flashcards
What is the function of haemoglobin?
To carry oxygen around the body.
Where is Hb?
RBC
What does Hb stand for?
Haemoglobin
What is Hb?
A large (globular) protein with a quaternary structure - it is made up of 4 polypeptide chains and 4 iron ions.
What does each polypeptide chain in Hb have?
A haem group, which contains an iron ion and gives Hb its red colour.
What gives Hb its red colour?
A haem group, which contains an iron ion and gives Hb its red colour.
What is the relationship between Hb and oxygen?
It has a high affinity for oxygen.
How many molecules of oxygen can each Hb molecule carry?
4
What do oxygen and Hb join to form in the lungs?
Oxyhaemoglobin
What type of reaction is it between Hb and oxygen?
Reversible
How is oxygen joining to Hb a reversible reaction?
As when oxygen leaves oxyhaemoglobin (dissociates from it) near the body cells, it turns back to Hb.
In what organisms is Hb found?
All vertebrates, earthworms, starfish, some insects, some plants and even in some bacteria.
What is the scientific name for RBC?
Erythrocytes.
How are RBC adapted for their function?
Biconcave shape to increase SA:V ratio.
Small and flexible shape to be squeezed through capillaries.
Missing a nucleus as are produced in the bone marrow leaving more space for oxygen.
Packed with Hb for oxygen transport.
How is oxygen transported around the body in Hb?
In the lungs, oxygen diffuses into the blood plasma then passes down a conc. gradient into RBC.
It binds to Hb to maintain this conc. gradient. It binds to the ‘haem’ Fe2+ group of the Hb.
In respiratory tissue, oxygen dissociates from the oxyhaemoglobin.
Oxygen can then diffuse out of the RBC and into the respiring cells.
What does Hb saturation depend on?
The partial pressure of oxygen.
What is the symbol for partial pressure of oxygen?
pO2
What is meant by the partial pressure of oxygen?
A measure of oxygen concentration.
How does Hb’s affinity for oxygen vary depending on the partial pressure of oxygen?
Oxygen loads onto Hb to form oxyhaemoglobin where there is a higher partial pressure of oxygen. Oxyhaemoglobin unloads its oxygen where there is a lower pO2.
What is the pO2 like in alveoli?
High so oxygen unloads onto Hb to form oxyHb.
What do dissociation curves show?
How affinity for oxygen varies.
What does 100% saturation of Hb mean?
Every Hb molecule is carrying the max 4 molecules of O2.
What is the shape of oxygen dissociation curves?
S-shaped.
Why is the oxygen dissociation curve S-shaped?
Because of conformational change.
Because when Hb combines with the first oxygen molecule, its shape (conformation) alters in a way that makes it easier for other molecules to join to. But as the HB starts to become saturated, it gets harder for the last oxygen molecule to join due to the reduced probability of an oxygen molecule hitting the final binding site. As a result, the curve has a steep bit in the middle where it is really easy for oxygen molecules to join, and shallow bits at each end where it is harder. When the curve is really steep, a small change in pO2 causes a big change in the amount of oxygen carried by the Hb.
What does an oxygen dissociation graph show the relationship between?
% saturation of Hb with oxygen and the pO2 (kPa).
Why does the oxyHb dissociation graph plateau just below 100% saturation?
As the Hb starts to become saturated, it gets harder for the last oxygen molecule to join due to the reduced probability of an oxygen molecule hitting the final binding site.
How does CO2 concentration affect oxygen unloading (dissociation)?
Hb gives up its O2 more readily at higher partial pressures of CO2.
Explain the Bohr effect
When cells respire they produce CO2 which raises the pCO2.
This increases the rate of oxygen unloading so the dissociation curve ‘shifts’ right. the saturation of blood with oxygen is lower for a given pO2 meaning that more oxygen is being released.
This is called the Bohr effect.
What is the Hb’s affinity for oxygen like for organisms that live in environments with a low conc. of oxygen and what does this mean for the dissociation curve?
They have Hb with a higher affinity for O2 than human Hb so the curve is to the left of ours.
What is the Hb’s affinity for oxygen like for organisms that are very active with a high oxygen demand and what does this mean for the dissociation curve?
Have Hb with a lower affinity for oxygen than human Hb so the curve is to the right of ours.
How is foetal Hb different to human Hb and what does this mean for the dissociation curve?
It has a stronger affinity for O2 than adult Hb so conc. gradient made with the mother, so O2 diffuses from adult blood to foetal blood.
Foetal curve is to the left of ours.
In what 3 ways is CO2 transported through the circulatory system?
5% dissolved in plasma.
10% associated with Hb to form carbaminohaemoglobin.
85% as hydrogen carbonate ions.
How is 85% of CO2 transported through the circulatory system as hydrogen carbonates?
CO2 dissolves in water to form carbonic acid (carbonic anhydrase catalyst) and the carbonic acid releases H+ protons (acid dissociation).
What happens with oxygen and Hb when there are H+ ions present?
If H+ ions can bind with Hb, they must compete with oxygen.
How can H+ ions be produced to compete with oxygen for Hb?
CO2 dissolves in water to form carbonic acid (carbonic anhydrase catalyst) and the carbonic acid releases H+ protons (acid dissociation).
Why is there competition between H+ ions and oxygen in respiring tissue?
Because more CO2 is produced so more carbonic acid is formed which means more H+ ions are dissociated so there is more competition for Hb so there is more oxygen dissociation.
