Flashcards in 10. The Variety Of Life Deck (35):
Describe the primary structure of a haemoglobin molecule:
Primary structure: four polypeptide chains.
Describe the secondary structure of a haemoglobin molecule.
Secondary structure: in which each of these polypeptide chains is coiled into a helix.
Describe the tertiary structure of a haemoglobin molecule.
Tertiary structure: in which each polypeptide chain is folded into a precise shape - an important factor in its ability to carry oxygen.
Describe the quaternary structure of a haemoglobin molecule.
Quaternary structure: in which all polypeptides are linked together to form an almost spherical molecule. Each polypeptide is associated with a haem group- which contains a ferrous (Fe2+) ion. Each Fe2+ ion can combine with a single oxygen molecule (O2) making a total of four O2 molecules that can be carried by a single haemoglobin molecule in humans.
What is the role of haemoglobin?
To transport oxygen.
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.
As a result of which property are the requirements of haemoglobin achieved?
It changes it's affinity for oxygen under different conditions. It's shape changes in the presence of certain substances, for example, carbon dioxide.
At the gas exchange surface where the oxygen concentration is high and carbon dioxide concentration low what is the affinity of haemoglobin and what is the result of this?
High haemoglobin affinity for oxygen - oxygen is attached.
At respiring tissues where oxygen levels are low and carbon dioxide levels are high what is the affinity of haemoglobin for oxygen and what is the result?
Low haemoglobin affinity for oxygen and so oxygen is released.
Describe haemoglobins with a high oxygen affinity.
These take up oxygen more easily but release it less readily.
Describe haemoglobins with a low oxygen affinity.
These take up oxygen less easily but release it more readily.
There is a correlation between...
The type of haemoglobin in an organism and factors such as the environment in which it lives or it's metabolic rate.
An organism living in an environment with little oxygen requires...
A haemoglobin that readily combines with oxygen if it is to absorb enough of it.
(Provided that the organism's metabolic rate is not very high, the fact that this form of haemoglobin does not release it's oxygen as readily into the tissues will not be a problem.)
An organism with a high metabolic rate needs...
Haemoglobins with a low oxygen affinity. Oxygen must be readily released into its tissues. As long as there is plenty of oxygen in the organism's environment, it is more important that the haemoglobin releases oxygen readily rather than taking it up readily.
Why do different haemoglobins have different affinities for oxygen.
Different haemoglobin molecules have slightly different sequences of amino acids and therefore slightly different shapes.
What is loading/associating?
The process by which haemoglobin combines with oxygen.
What is unloading/dissociating?
The process in which haemoglobin releases it's oxygen.
When haemoglobin is exposed to different partial pressures of oxygen...
It does not absorb the oxygen evenly.
How does haemoglobin absorb the first oxygen molecule at very low concentrations of oxygen?
The four peptides of the haemoglobin molecule are closely united and so it is difficult to absorb the first oxygen molecule.
What happens after the first oxygen molecule is loaded?
The initial oxygen molecule causes the polypeptides to load the remaining three oxygen molecule very easily.
What is the loading/unloading graph of oxygen to/from haemoglobin named?
The oxygen dissociation curve.
In the oxygen dissociation curve why does it level off at the top?
The haemoglobin is almost saturated with oxygen.
What occurs in the middle of the oxygen dissociation curve?
A very small decrease in the partial pressure of oxygen leads to a lot of oxygen becoming dissociated from haemoglobin.
There are a number of different types of haemoglobin molecules...
Each with a different shape and hence, different affinity for oxygen.
The shape of any one type of haemoglobin can change under different conditions.
What are there a large number of because of the variability of haemoglobin molecules?
There are a large number of different oxygen dissociation curves. They all have a roughly similar shape but differ in their position on the axes.
If an oxygen dissociation curve is far to the left what is the oxygen affinity?
The further to the left, the greater the oxygen affinity.
If an oxygen dissociation curve is far to the right what is the oxygen affinity?
The further to the right, the lower the oxygen affinity.
Haemoglobin has a ............ Affinity for oxygen in the presence of carbon dioxide.
Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.
E greater the concentration of carbon dioxide...
The more readily the haemoglobin releases its oxygen.
At the gas exchange surface (lungs) how high are carbon dioxide levels? What effect does this have on the oxygen affinity of the haemoglobin?
The level of carbon dioxide is low because it diffuses across the exchange surface and is expelled from the organism. Therefore the oxygen affinity is increased, which, coupled with the high concentration of oxygen in the lungs, means that oxygen is readily loaded by haemoglobin. The curve is to the left.
In rapidly respiring tissues the level of carbon dioxide is high. What is the oxygen affinity of haemoglobin near these tissues?
The affinity for oxygen is low, the coupled with the low oxygen concentration in the muscles means oxygen is readily unloaded from the haemoglobin into the muscle cells. The curve is to the right.
Explain this statement: the greater the concentration of carbon dioxide, the more readily haemoglobin releases it's oxygen.
Dissolved carbon dioxide is acidic and the low pH causes haemoglobin to change shape.
If carbon dioxide concentration is high, where does the oxygen dissociation curve shift to?
The right, the lower pH changes the shape of haemoglobin to one with a lower affinity for oxygen. Oxygen is released to highly respiring tissues readily.
Tell me the carbon dioxide/affinity for oxygen in haemoglobin cycle/progression.
The higher the rate of respiration --> the more carbon dioxide the tissues produce --> the lower the pH --> the greater the haemoglobin shape change --> the more readily oxygen is unloaded --> the more oxygen is available for respiration.