Haemoglobin Flashcards
Haemoglobin shape
- biconcave shape, maximise SA:Vol
- flexible to fit down narrow capillaries
- no nucleus- other organselles, maximise space for Hb
- complex protein with quaternary structure (four subunits, each containing a haem group)
Haemoglobin and Oxygen
- Hb has an affinity to O2
- Hb must readily associate with O2 and dissociate O2 at respiring cells
Hb + O2 -> Oxyhaemoglobin (associate)
Oxyhaemoglobin -> Hb + O2 (dissociate)
Percentage Saturation
% saturation of Hb with O2
oxygenated Hb/ max saturation x100
(Hb with 3 O2 + Hb with 4 O2 = 7/8x100)
Partial pressure of O2 (pO2) definition
The amount of oxygen in a mixture of gases or a solution
Oxygen in blood
The more oxygen there is in the blood, the more the oxygen is LOADED onto haemoglobin. The haemoglobin becomes more saturated.
Lower pO2 MEANS less haemoglobin is saturated
pO2 graph
Low pO2:
- low affinity
- low saturation
- unloading in cells
High pO2 in lungs:
- high pO2
- high affinity
- high saturation
- loading in lungs
(where curve flips= lower pO2 in tissue when at rest)
Loading / association definition
: When oxygen is taken up by haemoglobin
Unloading / dissociation definition
When oxygen is released/given up by haemoglobin
Loading
- High O2 Concentration (High pO2) – More oxygen loaded onto Hb
- Low O2 Concentration (Low pO2) – Less oxygen loaded onto Hb
Unloading
As well as haemoglobin loading oxygen, oxyhaemoglobin must also be able to unload oxygen so the tissues around the body can use it.
If oxyhaemoglobin moves to an area of low O2 concentration, then oxygen will be unloaded to the surroundings
Haemoglobin structure Graph description
PROTEINS OFTEN CHANGE SHAPE WHEN THEY BIND TO OTHER SUBSTANCES
oxygen dissociation curve is always ‘S’ shaped and is described as a ‘sigmoid curve’
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.
Explain why.
- Binding of first oxygen changes tertiary structure of haemoglobin;
- Exposes 2nd and 3rd O2 binding sites. making it easier for 2nd/3rd O2 molecules to bind
referred to as:
cooperative nature of oxygen loading.
Explain how the graph provides evidence for the change in shape making it easier for O2 to bind
- at low pO2 little increase in saturation as O2 increases
- rapid increase as it gets easier for O2 to bind
Effect of Increased Respiration on Oxygen Dissociation
- Tissue cells respire aerobically, quickly reducing the dissolved O2 in the surrounding the tissue fluid.
- This reduces the pO2 to a level lower than normal
- The oxygenated blood arriving with fully saturated haemoglobin will begin to unload more oxygen (become less saturated) and more oxygen will be released from the haemoglobin to the tissue cells. This is because the surrounding pO2 is lower and so haemoglobin will have an even lower affinity to oxygen.
% saturation at either a low or high pO2 calculation from graph
draw a line from a low or high pO2 up the sigmoid curve and across to the Y axis to see the effect on Hb % saturation.
Calculate the difference between these 2 points.
Lungs – tissues = % of oxygen unloaded
Bohr shift
- The more that tissue cells respire, the more the carbon dioxide concentration will increase and cause a shift to the right in the haemoglobin-oxygen dissociation curve.
- Hb now has a lower affinity to oxygen at the respiring cells.
- As a result, more oxygen is unloaded from the haemoglobin as it becomes less saturated.
- MORE oxygen is now available to meet the oxygen demands of the respiring cells/tissues.
Why does Hb have a lower affinity to O2 at high levels of CO2?
When CO2 dissolves in the blood it makes the blood acidic, thus lowering the pH.
As Hb is a protein, a change in pH slightly alters its tertiary structure
Heat from respiration helps mammals to maintain a constant body temperature.
Use this information to explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins.
- Smaller mammal has greater surface area to volume ratio
- Smaller mammal more heat lost
- Smaller mammal has greater rate of respiration
- Oxygen required for aerobic respiration
- Haemoglobin releases more oxygen
Describe the advantage of the Bohr effect during intense exercise.
- Increases dissociation of oxygen;
- For aerobic respiration at the tissues/muscles/cells
Different Hb have different affinities to Oxygen.
- This type of haemoglobin is found in adult humans and many other species that live on land at sea level.
- This is found in species that live in environments where the environmental pO2 is lower (high altitude, bottom of lakes, etc)
- They have a form of haemoglobin where the dissociation curve is shifted to the left.
- Their Hb has a higher affinity for O2.
- It becomes fully saturated at a lower pO2 and rapidly unloads its oxygen when the haemoglobin passes into the tissues
- Human foetal haemoglobin has a curve similar to this
- species that have a higher metabolic rate. These are animals like cheetahs (very active) or small mice
In these animals:
- Hb has a lower affinity for O2
- So dissociates from the haemoglobin more readily
- O2 is more readily available to respiring cells
The oxygen dissociation curve of the foetus is to the left of that for its mother.
Explain the advantage of this for the foetus.
- Higher affinity / loads more oxygen;
- At high pO2;
- Oxygen moves from mother to foetus;
Explain how oxygen is loaded, transported and unloaded in the blood.
- Haemoglobin carries oxygen
- In red blood cells;
- Loading in lungs;
- at high p.O2;
- Unloads to respiring cells/tissues;
- at low p.O2;
- Unloading linked to higher carbon dioxide conc.
Describe how haemoglobin normally loads oxygen in the lungs
- Oxygen combines to produce oxyhaemoglobin;
- each haemoglobin molecule may transport 4 molecules of oxygen;
- high partial pressure of oxygen concentration in lungs;
- haemoglobin 100% saturated;
- unloads at low oxygen tension in tissues
- presence of carbon dioxide increases oxygen dissociation;
- allows more O2 to be unloaded;
- increase acidity allows more O2 to be unloaded;
- low pO2 occur in vicinity of respiring tissue;
Explain how oxygen in a red blood cell is made available for respiration in active tissues
- CO2 (increased) respiration;
- (increased) dissociation oxygen from haemoglobin;
- Low partial pressure in tissues
- Oxygen diffuses from r.b.c. to tissues;
Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.
- more oxygen dissociation
- by increasing acidity
