Haemoglobin Flashcards
What is haemoglobin?
a large protein with a quaternary structure = it carries oxygen around the body
Describe the structure of haemoglobin
primary structure = amino acid sequence of the four polypeptide chains
secondary structure = polypeptide chains folded into an alpha helix
tertiary structure = each polypeptide chain is folded in a precise shape
quaternary structure = all four polypeptides are linked to form an almost spherical form. Each polypeptide is associated with a haem group, which contains Fe 2+ ion. Fe2+ can bind to oxygen. Therefore haemoglobin can bind to four o2 moles
What is the function of haemoglobin?
load oxygen in the lungs and deliver it to the respiring tissues
What does affinity mean?
the level of attraction haemoglobin has to oxygen
(high affinity = strong attraction, low affinity = weak attraction)
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What does loading/associating and unloading/disassociating mean?
loading/associating = when haemoglobin binds with oxygen
unloading/disassociating= when haemoglobin release its oxygen
Role of haemoglobin in oxygen transport?
haemoglobin has High Affinity in the lungs– due to high partial pressure of oxygen and low partial pressure of carbon dioxide,
so haemoglobin associates oxygen in the lungs and becomes saturated (full)
the haemoglobin is transported in the blood in the red blood cell
at the respiring tissues, haemoglobin has Low Affinity
– due to low partial pressure of oxygen and high partial pressure of carbon dioxide,
so oxygen is dissociated and haemoglobin becomes unsaturated
Why are there different haemoglobins which have different affinities?
change in the environment (e.g. ph or temperature) causes haemoglobin to change its tertiary structure and therefore affects the way it functions
different shape of the molecule due to a slightly different sequence in amino acid (primary structure) = different tertiary structure = different oxygen-binding properties
How do you know haemoglobin is a protein with a quaternary structure?
4 oxygen is able to binds to it (each polypeptide chain has a haem group which can bind to one o2 molecule)
Draw the oxygen dissociation curve for adult human haemoglobin
Explain the shape for the oxygen dissociation curve
low pressure -beginning of curve: the shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bind to one of the sites on its four polypeptide subunits because they are closely united, therefore low oxygen concentration means little oxygen binds to haemoglobin
higher oxygen partial pressure - Middle of the curve (when the gradient of the curve steepens): first oxygen molecule changes the Quaternary structure of the haemoglobin molecule = changes shape = easier or the other subunits to bind to an oxygen molecule **(positive cooperativity)**
End of the curve: longer for the oxygen molecule to bind to due to it being more difficult to find a binding site
What does it mean when the oxygen dissociation curve is more the left and when it is more the right?
left = greater affinity of haemoglobin for oxygen
right = lower affinity of haemoglobin for oxygen (unloads really easily)
What is the Bohr effect?
the greater the CO2 concentration, the more readily the haemoglobin releases its oxygen (as it has a lower affinity in the presence of CO2)
How does co2 concentration affect haemoglobin?
(mention pH)
low co2 concentration = haemoglobin changes shape into one of high affinity, so is able to load oxygen more readily, due to pH being slightly high
high co2 concentration = pH is lower as CO2 is acidic = lower affinity so oxygen disassociates more readily for the same partial pressure of oxygen, unloads more oxygen and has reduced saturation
Why does haemoglobin in the lungs have a higher affinity than haemoglobin in the respiring tissue?
Because in the lungs there is a low co2 concentration (due to the CO2 diffusing across the exchange surface and being excreted) and a high oxygen concentration
In respiring tissue, the co2 concentration is high (as the products of respiration is CO2 +water + energy) and the concentration of oxygen is low due to oxygen being used in respiration. This makes the affinity of haemoglobin in respiring tissue low
Why is low-affinity haemoglobin good for respiring tissues?
this means more readily oxygen is unloaded so more oxygen is available for respiriation