haemoglobin Flashcards
what is haemoglobin?
-a protein that is present inside red blood cells. It is a large globular protein with a quaternary structure (made up of more then one polypeptide chain) made up of 4, 2 alpha and 2 beta chains
-each polypeptide chain is attached to a haem group
What is a haem group?
-haemoglobin’s prosthetic group, making it a conjugated protein
-it contains iron which gives it its high affinity for oxygen
-each haem group is attached to a chain, and combines with a single oxygen molecule which means that 1 haemoglobin molecule can carry 4 oxygen molecules altogether
What is the reversible reaction for oxyhemoglobin?
Haemoglobin + oxygen = oxyhaemoglobin
What is meant by the term loading?
- Adding oxygen to haemoglobin
- happens in the lungs because oxygen moves down the concentration gradient of the alveolar air space and into the erythrocytes (red blood cells)
- the haemoglobin has an affinity for the oxygen and they become associated. There is no bond between them
What is meant by the term unloading?
- the loss of oxygen from haemoglobin
- happens in respiring tissues because oxygen moves down the concentration gradient from the erythrocytes (red blood cells) into the tissues where oxygen is constantly being used in aerobic respiration and it’s concentration remains low
- as the haemoglobin releases the oxygen it dissociates
What is myoglobin? State it’s structure and function
- A protein which acts as an oxygen store in muscle cells
- Only has one poplypeptide chain and haem group
- forms oxymyoglobin when it picks up oxygen from oxyhaemoglobin
- it has a higher affinity for oxygen than haemoglobin
Describe the path of a molecule of oxygen from alveolus to aerobic respiration.
1) Oxygen loads onto haemoglobin in the lungs to make oxyhemoglobin
2) oxygen travels in the blood in the form of oxyhaemoglobin to the muscles
3) oxygen dissociates from the oxyhaemoglobin to associate with myoglobin to make oxymyoglobin
4) oxygen is stored in the muscles in the form of oxymyoglobin
5) oxygen is released when the muscles are working hard to allow aerobic respiration to continue for longer before switching to a anaerobic respiration
What is the partial pressure of oxygen (po2) a measure of?
- Oxygen concentration
- the greater the concentration of dissolved oxygen in cells, the higher the partial pressure
What is the partial pressure of carbon dioxide a measure of?
Concentration of carbon dioxide in a cell
Explain how haemoglobins affinity for oxygen varies depending on the partial pressure of oxygen.
-When there is a high partial pressure of oxygen, oxygen loads onto haemoglobin to form oxyhaemoglobin
-When there is a low partial pressure of oxygen, oxyhaemoglobin unloads it’s oxygen
Where in the body is there a high partial pressure of oxygen, and a low partial pressure of oxygen?
-alveoli have a high partial pressure of oxygen, allowing for oxygen to be loaded onto haemoglobin
-respiring cells have a low partial pressure of oxygen, so oxygen is unloaded from haemoglobin for respiration
What does an oxygen dissociation curve show?
-How saturated the haemoglobin is with oxygen at any given partial pressure
What does 100% saturation mean on an oxygen dissociation graph?
every haemoglobin molecule is carrying the maximum 4 molecules of oxygen
What does it mean when the partial pressure of oxygen is high on an oxygen dissociation graph?
Haemoglobin has a high affinity for oxygen, and it will readily combine with oxygen, so it has a high saturation
Describe and explain the shape of haemoglobin on an oxygen dissociation graph
- has a sigmoid or ‘s’ shaped curve
- the first part of the graph is because haemoglobin has a very low affinity for oxygen at low oxygen concentrations
- when haemoglobin combines with the first oxygen molecule, its shape alters in a way that makes it easier for other molecules to bind too (known as cooperative binding)
- as the haemoglobin starts to become saturated, it gets harder for more oxygen molecules to join
- as a result the curve has a steep bit in the middle where it’s really easy for oxygen molecules to join, and shallow bits at the end where it’s harder. -When the curve is steep, a small change in partial pressure of oxygen causes a big change in amount of oxygen carried by the haemoglobin
- at high partial pressure, there is a high affinity for oxygen and it is difficult to offload it, producing the flat part of the ‘S’ curve.