well welcome to another MedCram lecture we're going to talk about the effect of
different things on the oxygen hemoglobin dissociation curve okay so
we've got a red blood cell from end on kind of also looks like that with a
little bit of a bulge in the middle and that's because it's lost its nucleus
what this is you have to remember is simply a bag of hemoglobin it's got no
nucleus it's got no mitochondria so the only form of energy that it can do is
glycol Isis or glycolysis and remember that's where we get glucose and it goes
to basically goes to pyruvate and that gives off forms of ATP this is not
oxidative phosphorylation this is substrate level phosphorylation but it
gives the cell the ATP that it needs and that's important because there's an
intermediate in this glycolysis that's actually going to do something story
hemoglobin binding curve which we're going to talk about next but before we
get to that I wanted to explain to you what the hemoglobin molecule looks like
if you can kind of imagine it's four different subunits that are connected to
each other okay and usually there's two alphas and two betas but that's not
important right now so there's for binding spots for oxygen
to bind to so if it binds to the first spot what happens is it causes a
conformational shift with the next one that causes oxygen to bind more affinity
and that causes a conformational shift with the next one which causes the
oxygen to bind even more affinity and finally that causes a conformational
shift that causes the last one to bind with even more affinity and so what
happens is you get something called cooperativity
the other turn that they like to use in biochemistry is called allosteric
interaction in this case it's not allosteric inhibition because it's
actually making these globin molecules more apt to bind the oxygen molecule the
other thing that you might want to be aware of is sometimes they have
different terms for these hemoglobin sub units if they are not bound to oxygen
they're known as the tense form or T and if they get bound to oxygen then they're
known as R or the relaxed form the other thing that happens that you may want to
know is that when an oxygen binds to this hemoglobin molecule a little carbon
dioxide molecule comes off a little co2 and you should probably know that that's
known as the Haldane effect just some trivia there so that when oxygen binds
to hemoglobin it releases co2 and if you see the co2 go up a little bit that's
known as the Haldane effect but let's talk about the human lobe and binding
curve so the way that this is represented we've kind of talked about
this before in the other lecture on delivery of oxygen is there's a
relationship between the partial pressure of oxygen in the blood and the
saturation of the humic loeben molecule so this is saturation here and this is
PA o2 and we can take that all the way up to a hundred so this is a hundred
this would be 50 this would be twenty five seventy five this is the po2 what
we're talking about here and up to about eighty we're starting to see here that
there's a kind of a curviness to this hemoglobin binding curve and so
the key points here that I want to show you is that there's this sort of a
plateau area here where increasing levels of po2 will not yield much more
in terms of the saturation so there's kind of a diminishing marginal utility
in sociated with that the other thing I want you to sort of notice is that if we
were to shift this human blown hemoglobin binding curve to the right in
other words if it were to go from this point
to this point notice that in fact what you're seeing here is you're seeing the
hemoglobin molecule as a whole being more apt to release oxygen it's more apt
to release oxygen and why is that because at any given po2 let's say 50 in
this case you'll see that in the blue hemoglobin binding curve has a lower
saturation then the yellow hemoglobin binding curve and so therefore the blue
hemoglobin binding curve is more apt to be less saturated at a given po2 than
the yellow hemoglobin binding curve and that's important because what's actually
happening as this thing is shifting back and forth as it goes through the
bloodstream depending on where it is so this is kind of something that you
should know so here's a question what are some things that are going to shift
the hemoglobin binding curve to the right and remember these are things that
make it less affinity so the things that make the hemoglobin binding curve less
affinity to oxygen or all of the things that you would expect to find in the
blood where oxygen needs to be given off by the hemoglobin molecule and that
would be in the muscles or placenta and what are they what do you find in the
muscles are you going to see a high or a low pH you're going to see a low pH
because this is where lactic acid is being produced this is where carbon
dioxide is being given off and we know that carbon dioxide is a Lewis acid
number two we would see a high temperature okay your muscles are hot
right when they're working so that would shift it to the right we already said
that a high partial pressure of carbon dioxide is going to shift the hemoglobin
binding curve to the right another thing that shifts it to the
right is a molecule called D e P G die phosphoglycerate otherwise
known as to 3b PG or bisphosphoglycerate this as you may recall is an
intermediate of glycolysis and this is where 3-phosphoglycerate
goes to to phosphoglycerate and that's an important step in glycolysis because
as that happens and as you have this buildup of 2 3 BPG which is by the way
seen elevated in pregnancy which makes sense because in pregnancy you're going
to want your hemoglobin molecule to be able to give up more oxygen to the fetus
you're going to do that you're going to see this increased in pregnancy and
you're going to see your hemoglobin molecule giving up more oxygen to the
fetus and you're going to see this hemoglobin molecule shift to the right
okay now what are some things that you would see cause it to shift to the left
these are things that you would see in the lungs so for instance in the lungs
you're breathing off carbon dioxide you could have a low acidity so you're going
to have a high pH of course in the lungs you're breathing in air which is cooler
than body temperature so generally speaking you're going to have a low
temperature number 3 as we already mentioned we're going to have a low
partial pressure of carbon dioxide and of course 4 we're not going to see maybe
possibly as much DPG and so you're going to see a shift to the left
the other thing that'll shift it to the left is fetal hemoglobin so H not a but
actually F which is way out here ok and that's fetal hemoglobin sucks up that
oxygen like no other human globin as it comes by the placenta so that is the
hemoglobin molecule and the disassociation curve thanks for joining
us you
you