it's 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
glycolysis or a 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
flea 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 holiday in effect but let's talk about the hemoglobin 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
hemoglobin 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 25 75 this is the po2 what we're talking about here and up
to about 80 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 adding any given po2 let's say
50 in this case you'll see that in the blue hemoglobin binding
curve has a lower saturation than 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 are 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 gonna see a high or a
low pH you're gonna 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 P G dye
phosphoglycerate otherwise known as 2 3 B PG or bisphosphoglycerate this as you
may recall is an intermediate of glycolysis and this is where
3-phosphoglycerate goes to 2 phosphoglycerate and that's an important
step in glycolysis because as that happens and as you have this buildup of
2 3 B P G 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 get more oxygen to the fetus you're going to
do that you're gonna see this increased in pregnancy and you're going to see
your hemoglobin molecule giving up more oxygen to the fetus and you're gonna see
this helical 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're gonna have a low acidity so you're gonna 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 gonna have a low temperature number three as we
already mentioned we're gonna have a low partial pressure of carbon dioxide and
of course four we're not gonna see maybe possibly as much DPG and so you're gonna
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 okay
and that's fetal hemoglobin sucks up that oxygen like no other human loeben
as it comes by the placenta so that is the hemoglobin molecule and the
disassociation curve thanks for joining us
you
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