- [Instructor] What I've drawn here is the chemical
structure for a triacylglyceride and recall
that this chemical structure is commonly what we
are referring to when we talk about the type of fat
found in our food as well as how fat is stored in our body.
Now the question I wanna begin to answer in this video
is how do we extract ATP, the chemical energy,
from this molecule because you've probably heard
that fats are a very rich source of energy
but how exactly do we get ATP from a structure like this?
Well the first thing I wanna point out is that 95%
of the chemical energy that we can extract
from this molecule comes from these carbon, hydrogen-rich
chains that we usually refer to as fatty acid chains.
Now I'm gonna put under or beside this, that 95%
of our chemical energy, I'll just make symbol here,
of the energy that we can extract
comes from these fatty acid chains.
Of course that means the remaining 5% of chemical energy
that we can extract from this molecule
comes from this glycerol backbone right here,
so this tiny portion of the molecule is not gonna really
contribute a lot and it essentially can enter
actually glycolysis, potentially, where it can be oxidized
further to produce a little bit of chemical energy.
So because these fatty acid chains are contributing
to the bulk of the energy that we're extracting,
we're gonna focus on how we extract ATP
from these fatty acid chains in particular.
And now to help us kind of get a bird's eye view
of how we're able to extract ATP from these fatty acid
chains, I've actually went ahead and drawn out
a 16-carbon saturated fatty acid that our body
can synthesize, which is called palmitic acid.
Now if you think back to how we extracted chemical energy
or ATP from glucose, you might remember that we oxidized
glucose, we essentially stripped it of its electrons
and we transferred those electrons to electron carrier
molecules to form reduced intermediates like NADH
and FADH2 and these carried the electrons
found in that glucose to the electron transport chain,
where we were able to produce ATP quite efficiently.
Ultimately, we just simply wanna do the same thing
with our fatty acid, we wanna be able to oxidize it,
extract all of those electrons, transfer them to those
electron carrier molecules, NADH and FADH2,
to be able to be used to produce ATP
in the electron transport chain.
And from a bird's-eye view, I think the big picture
takeaway is to realize that we wanna do is essentially
the reverse of fatty acid synthesis,
we wanna be able to take this long string of carbons
and hydrogens and essentially break them down
into two carbon sub-units each and as we break them up
into these two carbon sub-units, we're also simultaneously
oxidizing them to release all of this energy,
and ultimately what we're doing is we're breaking up
this large fatty acid into single molecules of acetyl-coA,
and if you remember the structure of acetyl-coA
looks something like this, so two carbons,
one attached to an oxygen, and of course we have
our co-enzyme A group, which I'm abbreviating like this.
Now notably, the energy extraction process
doesn't stop there, remember that acetyl-coA
is quite a versatile metabolyte when it comes to metabolism.
Remember that this is what can enter the Krebs cycle,
so it can enter the Krebs Cycle in the mitochondria
and when it enters the Krebs cycle,
even more electron carrier molecules like NADH and FADH2
can be produced by further oxidizing this molecule
and so altogether, you can see that the amount of ATP
that's gonna be produced is gonna be enormous
because we're getting electron carrier molecules
both from the direct oxidation into acetyl-coA
as well as acetyl-coA's own oxidation in the Krebs Cycle.
And to give you an idea of how much ATP we're really
talking about, I've went ahead and calculated
that for each run through the Krebs Cycle,
we can produce about a net of 10 ATP per acetyl-coA
molecule and we're producing one, two, three, four, five,
six, seven, eight, eight of these pairs of acetyl-coA
carbons and so altogether, we're producing about 80 ATP
in the Krebs Cycle alone and then add that to the amount
of ATP that's produced in this direct oxidation
into acetyl-coA and that happens to be about 27 ATP.
And I've calculated these numbers based on counting up
how many NADH and FADH2 molecules are produced at each step
and then multiplying that by a conversion factor
and the commonly accepted conversion factor
is that they're about 2.5 ATP per molecule of NADH produced
and 1.5 ATP per FADH2, but the big point
that I really wanna drive home here is that in the end,
ultimately, we are producing 80 plus 27, which is 107 ATP
molecules in total just from the oxidation
of one 16-carbon fatty acid.
Now compare that to the amount of ATP that we produce
from one molecule of glucose, one molecule of glucose
gives us about 30 to 32 molecules of ATP
so that's per one molecule of glucose.
So you can see here how much more ATP
that we can extract from this fatty acid.