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# Calculating ATP produced in cellular respiration

Created by Jasmine Rana.

Video transcript

alright so if we were going to go on the
ambitious task of telling up how much ETP was produced in one cycle of
cellular respiration or just to be super clear here I mean how much ETP was produced per the oxidation or
breakdown of one molecule of glucose in cellular respiration we might start off by just get yourself
organized and remind yourself that there are two kind of main ways that we
produce ATP and cellular respiration so the first minor contribution comes from
something called substrate level phosphorylation and remember that this
is exactly what it sounds like we have a substrate or a molecule i'm just going
to say our and remember that in the context of cellular respiration this is
usually we think this is it kind of metabolites an intermediate metabolite
of glucose so somewhere along glucose oxidation we get a metabolite and we
activate this metabolite with a phosphate group and from the phosphate
group we can actually donate it directly to adp to produce ATP and of course our
molecule also gets modified in the process usually gaining a hydroxyl group
but the details aren't entirely important except to realize that this
phosphorylation is occurring at the level of a substrate this is in contrast of course to
oxidative phosphorylation which is where we get the bulk of our ETP and in this
oxidative refers to the fact that this process requires oxygen and in fact the
importance of oxygen here is that this oxygen is reduced my electron carrier
molecules in something called the electron transport chains so remember that we have electron
carrier molecules called n-ath and fadh2 that are produced at various
stages of cellular respiration glycolysis the oxidation of pyruvate the
krebs cycle and it's basically storing up all of that energy from the glucose
molecule and it's going to donate it into with the electron transfer chain
and of course the final electron acceptor is oxygen which is then reduced
to water but the important part here is that this flow of electrons is able to
power something essentially fuel something called ATP synthase which is
an enzyme that is in the mitochondrial membrane that produces the bulk of our
ETP now the next point I want to make here is that it's actually been possible
for us to calculate the exact number of ATP producing substrate level
phosphorylation and we've also nailed down the amount of nadh and fadh2
molecules that are produced in this process as well but for quite a while it
was difficult to nail down the exact number of ATP molecules that were
produced in oxidative phosphorylation and for this reason actually i'll get
back to kind of why were unable to you know kind of nails and a number here but
for this reason you might often see quite a range of predictions for how
much etps actually produced in one cycle of cellular respiration just to give you
an idea that you know when I look at some textbooks you can see a range of
anywhere from 30 to 38 molecules of ATP that are predicted to be produced for
the oxidation of one molecule of glucose of course to get back to this kind of
elusive calculation of PTP researchers have done controlled studies in which
they basically take a known amount of energy to or fadh2 and they have my
country available in the lab and they basically allow the mitochondria to
oxidatively phosphorylate these molecules and essentially measure how
much ATP is produced but kind of to their surprise at first
they found that for nadh for one molecule of nadh they calculated there
was not a whole number of ATP produced in fact they found that there was
somewhere between two to three ATP molecules produced for everyone any deets molecule and for fadh they
also found that there was no hole integer number of ATP but rather there
was a range somewhere between 12 2 ATP produced now for the longest time
researchers kind of looked at these results and said you know whole numbers
are a lot easier to deal with and so why don't we just assume for the sake of
assumption that we can kind of round up and will say that for every one molecule
of nadh let's say that we have three molecules of ATP produced and for every
molecule of fadh2 rather we have two molecules of ATP produced and so using
these kind of estimations they calculated essentially the upper range
of ATP so these calculations were ultimately used to calculate kind of
this number of 38 ETP produced in cellular respiration kind of the upper
limit of ATP produced but of course we still have this range in fact it's worth
kind of pausing to stop and think about for a second if it is surprising that we
have this range in the first place and so to think about this a little bit
further I want to go ahead and kind of just draw out without getting too
detailed kind of a depiction of what's going on in the electron transport chain
so remember that the electron transfer chain is taking place in the
mitochondria in the mitochondria has two membranes we have the inner
mitochondrial membrane to my label here it's I and we have the outer
mitochondrial membrane and along the inner mitochondrial membrane we have a
series of proteins that are known as protein complexes and you know these all have specific
names but just for our purposes it's important to recognize their kind
of just for mean protein complexes and in some textbooks people will actually
call ATP synthase which i'm going to go ahead and draw here in yellow as complex
number five so let's let me go ahead and label these
one through five just so we remember that so these four
represent the protein complexes that shuttle electrons and of course 5
represents ATP synthase now recall that the basic premise here is that these
reduced electron carriers donate electrons to the electron transfer chain
and in fact specifically nadh donates to electrons to protein complex number one
and fadh2 donates to electrons to protein complex number two now the second important point is that
as these electrons are kind of flowing down these proteins for every two
electrons that kind of flow by it's actually been calculated that protein
complex number one pumps for protons into the intermembrane
space protein complex three pumps also for protons and protein complex number
four pumps two protons and protein complex number two doesn't really
contribute now with the facts in mind we can go
ahead and actually calculate how many protons are pumped for a molecule of
fadh2 and how many protons are pumped for molecules of NADH so let's go ahead
and just quickly do that here so because any d.h donates at the very first
electron complex it contributes to a total of four plus four plus two or 10
protons are pumped out for every molecule of nad ph on the other hand fadh2 enters in complex number two so it would only contributes to the
total pumping of six protons and so we can say that there are six protons that
are pumped for every molecule of fadh2 all right so here's a good place to
pause and kind of get back to the original question which was we have this
kind of range of ATP molecules produced per molecule of nadh or fadh2 and why is
it that you know we don't have a whole number integer ratio between the amount of ATP
and NADH that we have and the reason kind of that we might be able to justify
this looking at our diagram here is that nadh and fadh2 each contribute to this
proton gradient but really it's not any teacher f ed - that's directly donating
anything to form ATP because remember that it's this proton gradient that
forms in the intermembrane space here that essentially fuels is ATP synthase
remember that protons flow back through this ATP synthase molecule and in doing
so they essentially power this pump to phosphorylate adp into ATP and so and so
of course maybe the question we should really be asking is how many protons
does it take or how many pretending to flow through this ATP synthase to
phosphorylate one molecule of ATP into ATP and so i'm actually gonna go ahead
back to our ratios appear and right out here that if we knew how many protons
weren't necessary to produce one molecule of ATP we would be able to
calculate essentially the ratio of ATP to nadh or fadh2 and it's this
calculation that I think researchers are actually still trying to know nail down and you know I'm sure
depending on the type of cell and a state of the cells the efficiency of
this process is going to be different and might you know change moment to
moment and so maybe maybe you know the expectation to have an exact number not realistic but researchers are pretty
confident with the number right now currently of four protons being
necessary to produce one molecule of ATP so i'm going to go ahead and just write
that in here and with this number we can actually go ahead and calculate the
ratio of ETP to nadh and so simply we have here for every molecules of NADH we
have 2.5 molecules of ATP and for every molecule of fh we have 6/4 or 1.5
molecules of ATP that are produced so remember that even though it was kind
of funky that we're talking about kind of two and a half ATP per molecule of any detour per
molecule of fadh2 really what this is alluding to is the role of this
chemiosmotic coupling or using this proton gradient to fuel ATP synthase and
because we're talking about protons now we need to factor in that we end up
getting these non whole-number ratios between ATP and NADH or fadh2 but with
these racers in mind i actually want to go ahead and calculate kind of the sum
total of ATP that we produce in cellular respiration so I've already gone ahead
and kind of created a table here and remember that we're talking about one
cycle of cellular respiration so it's a totally TP yield let's say / 1 molecule of glucose
remember and so I've already kind of written out
here how many ATP and electron carrier molecules are produced in glycolysis and
the oxidation of pyruvate and the Krebs and TCA cycle now let's go ahead and
using our ratios here let's go ahead and write out how much ETP we have so two atps to ATP into any
th using our conversion factors to x 2.5 which is going to be 5 ATP and then we have again five ATP and two ATP
here four min substrate level phosphorylation is to ATP and six nadh x
2.5 is going to yield 15 and 2 Fe teach two times the 1.5 is going to yield
three and so if we add all of this up we get
32 ATP now before I call it good i want to make
one more last nit picky . which is to realize that glycolysis remember takes
place in the cytosol so unlike the oxidation of pyruvate and the krebs
cycle which take place in the mitochondria the N ETH that's produced
by glycolysis much must actually be shuttled somehow into the inner
mitochondrial membrane in order to donate its electrons into the electron
transport chain but for some reason it turns out that the inner mitochondrial
membrane is actually not permeable to this molecule nadh so the body is
actually come up with something called shuttle transport systems to show this
NADH into the mitochondria and it turns out that depending on where the NAD each
is shuttled into the electron transfer chain so if we actually go back to our
diagram here some of the electrons from the NADH produced in glycolysis can be
shuttled into the first electron first protein complex and some of them are
actually shuttled into this third protein complex here and so depending on
whether it's you know shuttled earlier leader on in the electron transfer chain
a different number of protons will be pumped into the proton gradient remember and so the conversion factor for the
amount of ATP produced is going to be different depending on which shuttle is
used so I just want to make that point and have you be aware of the fact that
this number right here this number here is actually arranged
you can actually range from anywhere - 325 ATP produced per molecule of any
deej I'm going to go ahead and kind of the Justice to say that really the rain cheer is 32 32 ATP produced per one
cycle of cellular respiration and this right here is the generally accepted
number for the amount of ATP produced in one cycle of cellular respiration