- [Voiceover] All right, cellular respiration
includes the metabolic pathways of glycolysis,
the Krebs cycle, and the electron transport chain,
as represented in the figures.
So we have the figures here of,
glycolysis, the Krebs cycle,
and the electron transport chain.
If all of this looks completely foreign to you,
I encourage you to watch the videos on Khan Academy
on glycolysis, the Krebs cycle,
and the electron transport chain,
and on cellular respiration in general.
All right, but let's tackle this problem.
It's a nice review of all of those things.
In cellular respiration, carbohydrates
and other metabolites are oxidized,
meaning electrons are taken away from them,
and the resulting energy-transfer reactions
support the synthesis of ATP.
All right, using the information above,
describe one contribution of each of the following
in ATP synthesis.
All right, the first one.
Catabolism of glucose in glycolysis and pyruvate oxidation.
The second was oxidation of intermediates
in the Krebs cycle.
And the third one is formation of a proton gradient
by the electron transport chain.
Now, each of these statements seem kind of intimidating,
but they're really just saying, describe how
glycolysis and pyruvate oxidation
contribute to ATP synthesis.
Describe how the Krebs cycle, because the Krebs cycle
is essentially nothing but the oxidation
of these intermediates to produce things
that are useful for ATP synthesis.
And then the formation of the proton gradient
by the electron transport chain.
Well that's what the electron trans-prit (laughs),
that's what the electron transport chain does.
It takes high energy electrons from NADH or FADH2,
and then as those high energy electrons
go to lower and lower energy states,
it's pumping these hydrogen protons across the membrane
and when they come back in, that's used to synthesize ATP.
So let's just answer.
We have to describe one contribution of each.
So, let's first focus on glycolysis.
So if we look here, there's more than one contribution.
You see that it can phosphorylate
these two ADPs to two ATPs.
So that's one contribution we could list.
We could say that it's producing these NADHs.
It's producing these NADHs, which can provide
both the hydrogen proton and, more importantly,
the high-energy electrons
for the electron transport chain later on.
You see that right over here.
Or you could say that, well, look,
it's producing the Acetyl-CoA,
which can enter the Krebs cycle,
which is used to produce GTP
or more NADHs or FADH2.
So all of these are contributions,
and since we only have to list one,
I'll list the most direct and obvious one,
although you could list any of these,
is, I will list, so this is one contribution.
I'll say the phosphorylation,
phosphorylation
of two ADPs, two ADPs,
to two ATPs,
to two ATPs.
And I could list several more,
but that's a good one right over there,
we just have to have one contribution.
All right, oxidation of intermediates in the Krebs cycle.
So, the oxidation of the intermediates,
that's just talking about each of these things
keep getting oxidized, and as they get oxidized,
we can use that to reduce other things,
including NAD plus to NADH.
So, when you reduce it, it's gaining electrons.
Notice, NAD plus is positive
and then it becomes NADH, which is neutral.
And these NADHs are used later on
in the electron transport chain
to pump hydrogen protons across the membrane
which are then used in oxidative phosphorylation
to produce the ATP as they go back through the membrane.
So, you could talk about the NADHs or FADH2s,
or you could talk about the direct creation of GTPs
which could be used to create ATPs.
So any of that is fine.
So I'll just list one of them.
So, I'll write
reduction of
NAD plus
to NAD, NADH,
which is used in
electron transport chain,
in electron
transport chain
to pump hydrogen protons to get,
to create proton gradient,
to create proton
gradient, gradient.
And once again, I could talk about the GDP,
the GT (laughs), the GTPs being created.
I could talk about the FADH2 being created.
Formation of a proton gradient by
the electron transport chain.
Well, as the protons flow with the gradient back into,
back across the membrane, they power ATP synthase
which creates ATP from ADP.
So, as protons
flow
across membrane,
flow with gradient across membrane,
flow with gradient
across membrane,
and if you're actually taking the AP test,
you might want to just do it below,
so you might have more space,
but I'll just fill it in here.
As protons flow with gradient across membrane,
they drive,
they drive ATP synthase,
ATP synthase,
which,
which takes,
we can say oxidatively phosphorylates,
so I'll just write phosphorylates,
phosphorylates
ADP,
ADP to ATP.
And once again, if everything I'm saying here
sounds foreign, and if these diagrams
don't make a lot of sense to you.
If they don't trigger a pleasurable memory
in your head (laughs),
I encourage you to watch the videos (laughs)
on Khan Academy, where hopefully you'll get
a little bit more intuition for the things
that I am talking about.
All right, now let's see if we can tackle part b.
Use each of the following observations
to justify the claim that glycolysis
first occurred in a common ancestor of all living organisms.
So, nearly all existing organisms perform glycolysis.
So, it's much more likely,
so much more likely that this,
in order for this to happen,
maybe I'll write this.
In order, so for this one right over here,
in order
for this to be the case,
to be the case,
it is much more likely,
much more likely
that this
evolved in a common ancestor,
in common ancestor
and was passed down,
and was passed down, or you could say
selected for, even,
and selected for,
selected for,
rather than independently
coming about multiple times,
than independently,
independently
arising in multiple branches of the evolutionary change,
than independently arising
in multiple branches,
branches,
of tree of life.
Or let me say, multiple branches of evolutionary tree.
Evolutionary,
evolutionary tree.
The fact that all, nearly,
or they're saying nearly all,
nearly all existing organisms perform glycolysis.
In theory, it could have happened independently,
just because it gets selected so for strongly,
but if something happens in nearly all organisms,
it's very likely that it evolved at a very, very
early stage, at a kind of a primitive ancestor organism,
and that was selected for,
and it continues to be selected for
and that's why we continue to see it.
All right, glycolysis occurs under anaerobic conditions.
So actually, let me create some space here
so things don't get too jumbled up.
So glycolysis occurs under anaerobic conditions.
Well, early Earth,
early Earth
had little,
had little oxygen
little oxygen
in atmosphere.
Early life.
So, early life,
had to perform,
had to, I guess you could say,
produce ATP, or you could,
early life had to metabolize,
tab-ol-ize sugars or carbohydrates
in anaerobic environment.
In anaerobic, so an environment that doesn't have oxygen.
Anaerobic,
anareobic environment.
So that seems to, once again, justify the claim
that glycolysis first occurred in a common ancestor
of all living organisms.
Glycolysis only occurs in cytosol.
So, so most, so, earliest,
earliest life
didn't have
membrane-bound organelles,
membrane-bound
organelles,
so the fact that it only occurs in cytosol,
so fact that occurs
in cytosol
consistent with it be, that it's possible
that early life did it.
Is consistent
that earl, with early life
with it first occurring,
occurring in common ancestor.
First, with it first occurring
in common,
early ancestor.
I'll then tackle parts c and d in the next video.