3B: Mass transport Flashcards
Describe 3 adaptations of red blood cells
- Biconcave shape = maximises SA for gas exchange
- Small + flexible = to pass through narrow capillaries (pressed to the sides to maximise gas exchange)
- No nucleus = more room to carry respiratory gases
What is the function of red blood cells?
To transport O₂ around the body
How does haemoglobin allow RBCs to carry respiratory gases (especially oxygen)
- It has an affinity for oxygen (can carry up to 4 O2 molecules)
- Oxygen binds to the ‘haem’ Fe2 + group of haemoglobin
What is haemoglobin called when it becomes oxygenated?
Oxyhaemoglobin
What are the haemoglobins?
- The haemoglobins are a group of chemically similar molecules found in many different organisms.
- They are protein molecules with quaternary structures
Describe the primary structure of a haemoglobin molecule.
Sequence of amino acids in the 4 polypeptide chains
Describe the secondary structure of a haemoglobin molecule.
Each of the 4 polypeptide chains is coiled into a helix
Describe the tertiary structure of a haemoglobin molecule.
Each polypeptide chain is folded into a precise shape
Why is the tertiary structure of a haemoglobin molecule so important?
- The tertiary structure of a protein determines the 3D shape of the protein
- For haemoglobin this is an important factor in its ability to carry oxygen
Describe the quaternary structure of a haemoglobin molecule.
- All 4 polypeptides are linked together to form an almost spherical molecule
- Each polypeptide is associated with a haem group
What does each haem group, in haemoglobin, contain?
Each haem group contains a ferrous group (Fe2+) ion
- Each iron ion can combine with a single oxygen molecule
= a total of 4 O2 molecules can be carried
In humans, where does the loading/ associating of haemoglobin & oxygen take place?
In the lungs
In humans, where does the unloading/ dissociating of haemoglobin & oxygen take place?
In the tissues
What is the process by which haemoglobin binds with oxygen called?
Loading/ associating
What is the process by which haemoglobin releases its oxygen called?
Unloading/ dissociating
What is the role of haemoglobin?
To transport oxygen from gas exchange surafces to respiring tissues
To be efficient at transporting oxygen, haemoglobin must:
- Readily associate with oxygen at the surface where gas exchange takes place
- Readily dissociate from oxygen at those tissues requiring it
What adaptation allows haemoglobin to readily associate + dissociate from oxygen in different environments?
The fact that haemoglobin can change its affinity for oxygen under different conditions.
How does haemoglobin change its affinity for oxygen in different environments?
Because its shape changes in the presence of certain substances, e.g carbon dioxide
Describe what happens to haemoglobin in respiring tissue.
- In respiring tissue there’s a high CO₂ conc. and a low O₂ conc.
- In the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely to oxygen
- It has a low affinity for O₂
= resulting in the haemoglobin unloading its oxygen
Describe what happens to haemoglobin at the gas exchange surface.
- At the exchange surface there’s a high O2 conc. and a low CO2 conc.
- This means that the haemoglobin will have a high affinity for O2
= resulting in the haemoglobin loading its oxygen
Why do different hemoglobins have different affinities for oxygen?
Due to the shape of the molecule
Why do different organisms have haemoglobins with different shapes - and therefore oxygen affinities?
- Because each species produces a haemoglobin with a slightly different amino acid sequence
- Therefore the haemoglobin of each species will have a different tertiary + quaternary structure
= and hence different oxygen binding properties
What is the partial pressure of oxygen (PO2) referring to?
The amount of oxygen in the tissue