B2. Haemoglobin Flashcards
The role of haemoglobin
Many organisms have to transport substances over large distances to get them to and from their exchange surfaces. Mass transport systems, such as the ____________ system in animals, ensure the efficient movement of substances throughout the organism.
_______________is an important part of the circulatory system. Human haemoglobin is found in ___ ________ ____ its role is to carry _________around the body. There are many chemically similar types of haemoglobin found in many different organisms, all of which carry out the same function. As well as being found in all ______________, haemoglobin is found in earthworms, starfish, some insects, some plants and even in some bacteria.
Many organisms have to transport substances over large distances to get them to and from their exchange surfaces. Mass transport systems, such as the circulatory system in animals, ensure the efficient movement of substances throughout the organism.
Haemoglobin is an important part of the circulatory system. Human haemoglobin is found in red blood cells its role is to carry oxygen around the body. There are many chemically similar types of haemoglobin found in many different organisms, all of which carry out the same function. As well as being found in all vertebrates, haemoglobin is found in earthworms, starfish, some insects, some plants and even in some bacteria.
Haemoglobin and oxyhaemoglobin
Haemoglobin (Hb) is a large _________with a _____________structure - it’s made up of ____polypeptide chains. Each chain has a _____group which contains an ____ion and gives haemoglobin its red colour. Each molecule of human haemoglobin can carry _____oxygen molecules.
In the lungs, oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin. This is a reversible reaction near the _____ ____, oxygen leaves oxyhaemoglobin and it turns back to haemoglobin. When an oxygen molecule joins to haemoglobin it’s referred to as ____________ or __________, and when oxygen leaves oxyhaemoglobin it’s referred to as _______________ or ____________.
Haemoglobin (Hb) is a large protein with a quaternary structure - it’s made up of four polypeptide chains. Each chain has a haem group which contains an iron ion and gives haemoglobin its red colour. Each molecule of human haemoglobin can carry four oxygen molecules.
In the lungs, oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin. This is a reversible reaction near the body cells, oxygen leaves oxyhaemoglobin and it turns back to haemoglobin (see Figure 2). When an oxygen molecule joins to haemoglobin it’s referred to as association or loading, and when oxygen leaves oxyhaemoglobin it’s referred to as dissociation or unloading.
Affinity for oxygen and pO₂
Affinity for oxygen means the tendency a molecule has to bind with oxygen. Haemoglobin’s affinity for oxygen varies depending on the conditions it’s in one of the conditions that affects it is the partial pressure of oxygen (pO2).
pO2, is a measure of oxygen concentration. The greater the concentration of dissolved oxygen in cells, the higher the partial pressure. As pO2, increases, haemoglobin’s affinity for oxygen also increases
Describe the process of Hb (5 steps)
Oxygen loads onto haemoglobin to form oxyhaemoglobin where there’s a high pO2
Oxyhaemoglobin unloads its oxygen where there’s a lower pO2
1) Oxygen enters blood capillaries at the alveoli in the lungs.
2) Alveoli have a high pO2, so oxygen loads onto haemoglobin to form oxyhaemoglobin.
3) When cells respire, they use up oxygen - this lowers the pO2.
4) Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen.
5) The haemoglobin then returns to the lungs to pick up more oxygen.
Figure 3: Oxygen loading and unloading in the body.
Alveoli in lungs - (4 things)
Respiring tissue - (4 things)
Alveoli in lungs:
- HIGH oxygen concentration
- HIGH PO2
- HIGH affinity
- Oxygen LOADS
At respiring tissue:
- LOW oxygen concentration
- LOW PO2
- LOW affinity
- Oxygen UNLOADS
Dissociation curves
An oxygen dissociation curve shows how _____________ the ______________is with _________at any given ________ __________. The ___________of haemoglobin for oxygen affects how saturated the haemoglobin is
Dissociation curves
An oxygen dissociation curve shows how saturated the haemoglobin is with oxygen at any given partial pressure. The affinity of haemoglobin for oxygen affects how saturated the haemoglobin is
Dissociation curves
Where pO2 is high (3 things)
Where pO2 is low (3 things)
Where pO2 is high
- (e.g. in the lungs)
- haemoglobin has a high affinity for oxygen
- so it has a high saturation of oxygen.
Where pO2 is low
- (e.g. in respiring tissues)
- haemoglobin has a low affinity for oxygen
- so it has a low saturation of oxygen.
Dissociation curves
The saturation of haemoglobin can also affect the affinity - this is why the graph is ‘S-shaped’ and not a straight line.
Describe the events that make the graph is S-shaped (3) and extra information about it (1)
1) When haemoglobin combines with the first O2 molecule, its tertiary structure change making it easier for other O2 molecules to join.
2) The curve has a steep bit in the middle where it’s really easy for oxygen molecules to join
3) As the haemoglobin starts to become saturated, it gets harder for more oxygen molecules to join so there is shallow bits at each end
When the curve is steep, a small change in pO2, causes a big change in the amount of oxygen carried by the haemoglobin.
Figure 5: The S-shaped dissociation curve for haemoglobin.
Exam Tip
Always be specific in your exam answers. For example, don’t just say that human haemoglobin has a high affinity for oxygen - it only has …
Exam Tip
Always be specific in your exam answers. For example, don’t just say that human haemoglobin has a high affinity for oxygen-it only has a high affinity for oxygen in the lungs.
Carbon dioxide concentration - Bohr Effect in 3 steps
1) Respiring cells produce CO2 and increases the rate of oxygen unloading
2) Haemoglobin gives up its oxygen more readily at a higher pCO2 to get more O2 to cells during activity.
3) This results in the Bohr effect in which the dissociation curve ‘shifts’ right. This means haemoglobin’s affinity with oxygen is lower for a given pO2, meaning that more oxygen is being released.
Figure 6: The Bohr effect. - Relationship between saturation and pO2
Different types of haemoglobin - Low oxygen environments
What is the effect? (1)
An example using a lugworm?
Organisms that live in environments with a low concentration of oxygen have haemoglobin with a higher affinity for oxygen so it binds to oxygen more readily and their dissociation curve of their haemoglobin is to the left.
Example - A lugworm lives in burrows beneath sand where there’s a low oxygen concentration. Its haemoglobin has to be able to pick up as much oxygen as possible it has a high affinity for oxygen.
Tip: Environments with a low oxygen concentration are… (3 places)
- underground
- at high altitudes
- close to the seabed.
Tip: The curve shifts to the ______for organisms that live in Low oxygen environments. The curve shifts to the ______for organisms that have a high Respiration rate.
Tip: The curve shifts to the LEFT for organisms that live in LOW oxygen environments. The curve shifts to the RIGHT for organisms that have a high RESPIRATION rate.
Different types of haemoglobin - High activity levels
What is the effect? (1)
An example using a hawk?
Organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen so it unloads oxygen more readily to respiring cells and their dissociation curve of their haemoglobin is to the right
Example - A hawk has a high respiratory rate (because it is very active) and lives where there’s plenty of oxygen. Its haemoglobin has to be able to unload oxygen quickly in order to meet the high oxygen demand it has a low affinity for oxygen.
Reading values from a dissociation curve - Example-Maths Skills
The graph on the right shows the oxygen dissociation curves for two animals. At a pO2 of 6 kPa, what is the difference between the percentage saturation of haemoglobin with oxygen for the two animals?
- Find 6 kPa on the x-axis.
- Use a ruler to draw a line up to the curve for animal A. Make sure the line is parallel to the y-axis.
- Then draw a line across to the y-axis. Make sure this line is parallel to the x-axis.
- Read off the value at this point on the axis-84%-
- Repeat for the curve for animal B-60%.
6.Find the difference between them: 84-60-24%
