7.2- TRANSPORT OF OXYGEN BY HAEMOGLOBIN Flashcards
How does haemoglobin bind to oxygen when it’s exposed to different partial pressures of oxygen?
does not bind oxygen evenly
What is the graph of the relationship between the saturation of haemoglobin with oxygen + partial pressure of oxygen known as?
oxygen dissociation curve
Why is the gradient of the oxygen dissociation curve initially shallow?
shape of haemoglobin molecules makes it difficult for first oxygen molecules to bind to one of its sites on its four polypeptide subunits as they’re closely united
so at low oxygen conc., little oxygen binds to haemoglobin
What does the binding of the first oxygen molecules do?
changes quaternary structure of haemoglobin molecule, causing it to change shape
What does the change is shape after the binding of the first molecule to haemoglobin do?
makes it easier for other subunits to bind to an oxygen molecule
In other words what does the first oxygen molecule induce?
induces other subunits to bind to an oxygen molecule
What does it take to bind second oxygen molecule?
takes smaller increase in partial pressure of oxygen than it did to bind to first one
What is positive cooperativity?
binding of first molecule makes binding of second easier + so on
What happens to the gradient of the oxygen dissociation curve due to positive cooperativity?
gradient steepens
What happen after the binding of the third molecule?
in theory it’s easier for haemoglobin to bind to fourth oxygen molecule, in practice it’s harder
Why is it harder for the fourth oxygen molecule to bind?
due to probability
majority of binding sites occupied, less likely that single oxygen molecule will find empty site to bind to
What happens to the gradient of the oxygen dissociation curve as its harder for the fourth oxygen molecule to bind?
curve reduces + graph flattens off
What does it say about affinity for oxygen when the oxygen dissociation curve is further to left?
further to the left the curve, the greater is the affinity of haemoglobin for oxygen (so its loads oxygen readily but unloads it less easily)
What does it say about affinity for oxygen when the oxygen dissociation curve is further to the right?
further to the right the curve, the lower the affinity of haemoglobin for oxygen (so it loads oxygen less readily but unloads more easily)
In what presence does haemoglobin have a reduced affinity for oxygen?
in presence of carbon dioxide
What happens to haemoglobin the greater the conc. of CO2?
more readily haemoglobin releases its oxygen (Bohr effect)
What is the conc. of CO2 like at the gas-exchange surface (e.g. lungs)?
conc. of CO2 low
Why is the conc. of CO2 low at the gas-exchange surface (e.g. lungs)?
as it diffuses across the exchange surface + is excreted from organism
As the conc. of CO2 at the gas-exchange surface is low, what is the affinity of haemoglobin for oxygen like?
affinity of haemoglobin for oxygen increased, which, coupled with high conc. of O2 in lungs, means oxygen readily loaded by haemoglobin
What does the reduced CO2 conc. do to the oxygen dissociation curve?
shift oxygen dissociation curve to the left
What is the conc. of CO2 like in rapidly respiring tissues (e.g. muscles)
conc. of CO2 high
As the conc. of CO2 in rapidly respiring tissues (e.g. muscles) is high, what is the affinity of haemoglobin for oxygen like?
affinity of haemoglobin for oxygen reduced, which, coupled with low conc. of oxygen in muscles, means oxygen readily unloaded from haemoglobin into muscle cells
What does the increased CO2 conc. do to the oxygen dissociation curve?
shift oxygen dissociation curve to right
Why does haemoglobin readily release O2 more the greater the conc. of CO2?
as dissolved CO2 acidic + low pH causes haemoglobin to change shape
What is constantly being removed from the gas-exchange surface? (loading, transport and unloading of oxygen 1)
CO2 constantly being removed
What happens to pH due to low conc. of CO2? (loading, transport and unloading of oxygen 2)
pH slightly raised
What does a higher pH do to the shape of haemoglobin? (loading, transport and unloading of oxygen 3)
higher pH changes shape of haemoglobin into one that enables it to load oxygen readily
What else does the shape of haemoglobin from pH increase? (loading, transport and unloading of oxygen 4)
increases affinity of haemoglobin for oxygen, so it’s not released while being transported in blood to tissues
What is produced in respiring cells? (loading, transport and unloading of oxygen 5)
in tissues, CO2 produced by respiring cells
What condition does CO2 in solution make + what happens to pH of blood within tissue? (loading, transport and unloading of oxygen 6)
carbon dioxide acidic in solution, so pH of blood within tissue lowered
What does lower pH do to haemoglobin? (loading, transport and unloading of oxygen 7)
lower pH changes shape of haemoglobin into one with lower affinity for oxygen
What does haemoglobin release? (loading, transport and unloading of oxygen 8)
haemoglobin releases it oxygen into respiring tissues
What happens to haemoglobin as it passes through the lungs in humans?
becomes saturated with oxygen
In practice are all haemoglobin molecules loaded with their maximum four oxygen molecules?
no
What is the overall saturation of haemoglobin at atmospheric pressure?
normally around 97%
When haemoglobin reaches a tissue with a low respiratory rate, how many molecules would normally be released?
only one molecules normally released
As the haemoglobin usually only releases one molecule to tissue with low respiratory rate, what is the saturation of the haemoglobin in the blood returning to the lungs?
blood returning to lungs will contain haemoglobin that’s still 75% saturated with oxygen
If a tissue is very active e.g. exercising muscle, how many oxygen molecules will usually be unloaded from each haemoglobin molecule?
3 oxygen molecules will usually be unloaded from each haemoglobin molecule
What have species of animals living in environment with lower partial pressure of oxygen evolved about haemoglobin?
evolved haemoglobin that has higher affinity for oxygen than haemoglobin of animals that live where partial pressure of oxygen higher
How active is the lugworm?
not very active
Where does the lugworm spend almost all of its life?
in a U-shaped burrow
What is the lugworm covered in most of the time?
covered by sea water, which it circulated through its burrow
How does oxygen diffuse into the lugworm?
diffuses into lugworm’s blood from water
What does lugworm use to transport oxygen to its tissues?
uses haemoglobin to transport oxygen to its tissues
What can lugworms no longer do when tides go down?
lugworm can no longer circulate fresh supply of oxygenated water though its burrows
What happens to the water in the burrow when the tides go down?
water in burrow contains progressively less oxygen as lugworm uses it up
What must the lugworm do when the tides go down?
has to extract as much O2 as possible from water in burrow if it’s to survive until tide covers it again
What is the dissociation curve of the lugworm like in comparison to that of a human?
dissociation curve shifted far to left of that of human
What does it mean as the dissociation curve of lugworm is shifted far to the left of human’s?
haemoglobin of lugworm fully loaded with oxygen even when there’s little available in the environment
What conditions do llamas live in?
at high altitudes
What is the atmospheric pressure + partial pressure of oxygen like at high altitudes?
atmospheric pressure lower + so partial pressure of oxygen lower
As the atmospheric pressure lower + so partial pressure of oxygen lower at high altitude, what does this mean for haemoglobin?
difficult to load haemoglobin with oxygen
What is the affinity of oxygen for haemoglobin in llamas like in comparison to human haemoglobin?
haemoglobin has higher affinity for oxygen than human haemoglobin- shifted to left of human haemoglobin
