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Fat and protein metabolism
Current time:0:00Total duration:6:05
Overview of Fatty Acid Oxidation
Video transcript
- [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.