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MCAT
Course: MCAT > Unit 5
Lesson 16: Fat and protein metabolism- Fat and protein metabolism questions
- Introduction to energy storage
- Digestion, Mobilization, and Transport of Fats - Part I
- Digestion, Mobilization, and Transport of Fats - Part II
- Fatty Acid Synthesis - Part I
- Fatty Acid Synthesis - Part II
- Overview of Fatty Acid Oxidation
- Fatty Acid Oxidation - Part I
- Fatty Acid Oxidation - Part II
- How does the body adapt to starvation?
- Overview of Amino Acid Metabolism
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Fatty Acid Oxidation - Part I
What are the three phases required for fatty acid oxidation? Where in the cell do these reactions take place? How is this process regulated? Explore the three major phases of oxidizing and extracting ATP from fatty acids within a cell. Dive into the activation process, understand the role of coenzyme A, and learn about the transport process involving carnitine. Uncover the fascinating interplay between fatty acid synthesis and oxidation. Created by Jasmine Rana.
Want to join the conversation?
- Hi Jasmine thanks for the video! One question:
At the very end of this video you reference Carnitine Acyl Transferase I as the enzyme on the outer face of the inner mitochondrial membrane. Is there a difference between that enzyme and Carnitine Palmitoyltransferase I to acyl onto the carnitine or is it merely semantics?(8 votes)- > Carnitine Acyl Transferase I as the enzyme on the outer face of the inner mitochondrial membrane
Carnitine Acyl Transferase I is on the outer mitochondrial membrane, not inner mitochondrial membrane.(2 votes)
- my textbook says that carnation acyltransferase is located in the inner membrane.(4 votes)
- 1-Why do carnitine deficiency patients have brain dysfunction?
Is it because of hypoglycemia in fast periods?
2-Why do carnitine palmitoyltransferase 1 deficiency patients have muscles weakness if the deficiency is in the liver specifically?
3-Why do individuals with Refsum disease present with hyperketosis?
4-In Refsum syndrome, how do branched fatty acids pass through brain blood barrier?(1 vote)- for question one, while fasting and low activity state your body switches its energy source to almost 70-80% from fatty acid while supplying the brain with the available glucose, carnitine deficiency forces your peripheral tissues to use glucose instead of FA's while the liver can not compensate by gluconeogenesis leading to impairment in brain function.(1 vote)
- What happens to the fat stored in the body when people lose weight?(0 votes)
- When carnitine binds to acyl CoA, is the product acyl with an attached carnitine + SH-CoA? I'm trying to figure out what happens to the S-CoA...(1 vote)
- That is correct! The acetyl-CoA becomes HS-CoA. I wrote the "S" and the "H" in the order opposite to yours, but they are equivalent. :)(1 vote)
- In her example, she used a monosaturated fatty acids. However, would the ATP yields differ with monounsaturated or polyunsaturated fatty acids compared to monosaturated fatty acids?(1 vote)
- Not once did she mention this oxidation is known as Beta-oxidation which is how it's referred to in textbooks, and everywhere else. If she was teaching high school students or middle school students this would be fine and dandy, but if she is teaching at a pre-med level, this is grossly reduced to simple conversation lacking important terminology.(1 vote)
- A) Hedgehogs lose 25% of their body weight during their hibernation in the UK. It is possible for a hedgehog to survive up to a 40% loss of weight over the winter. All this energy comes from the β-oxidation of fatty acids. A hedgehog weighed 550 g at the start of the winter which it would have built up to survive a period of up to four months hibernation. In the event the weather was poorer and the winter lasted 5 months. You can assume that the oxidation of fat yields an average 38 kJ g-1 and that the hedgehog’s hibernating metabolism uses 49 233 J per day. Will this hedgehog have survived hibernation?
B) In hibernating hedgehogs the levels of the hormones adrenaline and noradrenaline was shown to be present at higher than normal, non-hibernating serum levels. Can you suggest a reason for this observation?
can you plz help me to solve this bioenergetic problem(0 votes)
Video transcript
- [Instructor] What I've
drawn out here are three compartments found inside of a cell. And what I want to go ahead
and do now is kind of label what I've drawn out here
because these three compartments are going to be very
important when discussing the three kind of major
phases involved in oxidizing and extracting ATP from fatty
acids inside of the cell. So starting up here, this
compartment I'm going to label as the cell's cytoplasm. And these two lines down
here are both representing the two membranes around the mitochondria. If you remember the
mitochondria has two membranes. It has the outer mitochondrial membrane facing the cytoplasm, and
then below it, it has the inner mitochondrial membrane. And I'm abbreviating these as OMM and IMM. And so, of course, the
space between these is the inter-membrane space. Now if you remember this is
where the proton gradient was built up for the
electron transport chain. And then finally, down here,
this is going to be the inside of the mitochondria,
which is something that we also commonly refer to
as the mitochondrial matrix. Now you might recall that fatty
acid synthesis takes place inside of the cytoplasm, where the enzymes required for that process are located. Now in the other hand it
turns out that the enzymes required for the oxidation
of fatty acids, to obtain all of that ATP from that
molecule, are located inside of the mitochondria. But remember that cells
take up fatty acids into their cytoplasm from the bloodstream. So we need some way to be
able to transport these fatty acids from the cytoplasm into the mitochondrial matrix. And this might look familiar to you. It might kind of ring a bell
from fatty acid synthesis because, remember in fatty
acid synthesis, we were also having to transport something
across the cytoplasm. Of course you were going
the opposite direction in fatty acid synthesis,
where we wanted to transport Acetyl CoA into the cytoplasm. But I actually want to come
back at the end of the video to touch on kind of the
seemingly rounded out way to have to transport things
across this mitochondrial membrane because it turns
out it has a very interesting implication for how our
body is able to regulate fatty acid synthesis and oxidation. And so I'll come back
again and touch on that. But just going back to
this transport process, it turns out that in order
to be able to transport these fatty acids across
this mitochondrial membrane, there's a specific pathway
that requires us to actually activate, so to say, a
fatty acid molecule with another molecule in order
for this transport machinery to work. And so all together, there
are kind of three major phases involved in being
able to ultimately extract ATP from a fatty acid. So let's go ahead and cover
these three phases in turn. Alright, so starting ofF
with the activation step, let me go ahead and draw
out the chemical structure of a fatty acid, starting
off with its carboxylate head group, and of course
it also long chain of carbons and hydrogens that
comprise its fatty acid tail, which we usually refer to it as. But instead of drawing this
tail out every single time or drawing or writing out
all the carbons or hydrogens, I'm just going to abbreviate
that using the letter R to keep things in our diagram simple. Now as I mentioned before,
the goal here is to activate this molecule, quote unquote, with another molecule so that
we're able to transport it into the mitochondria. So how does the body do that? Well the body does that by
reacting this fatty acid with one of the most versatile
metabolites in our body, which is coenzyme A. Because the structure of
this molecule is quite large, we end up just abbreviating
it as CoA, and usually at most textbooks will highlight
this one functional group, this sulfur hydrogen
group, this thial group because it's involved in
forming a bond with this carbon here. So let's kind of see what that looks like, what the product of this reaction is. So we end up preserving this acyl group, and the acyl group just
refers to this kind of part of the molecule here. We end up forming a
bond with the coenzyme A through this sulfur atom as such. And the name of this molecule is acyl-CoA. And I remember when I was
first learning about this, I confused this often with
acetyl-CoA, which, remember just has a methyl group
instead of this long fatty acid chain. So just keep those two
things in mind, making sure not to confuse this
acyl-CoA with acetyl-CoA. Now as a quick disclaimer, I
want to apologize in advance for any stoichiometry
calculations that don't seem to be right. Perhaps like this oxygen atom here. Where is this oxygen atom going? And that's due in part because
I'm abbreviating some things in these molecules and so the oxygen atoms might be hidden somewhere. But mostly it's due to the
fact that I'm not going over the entire mechanistic
pathway by which this reaction occurs. It ends up that there are
a couple steps involved in this reaction. And so I encourage you,
if there's something that doesn't make sense, in
terms of the stoichiometry, to just do a quick google search and the entire mechanism will be illuminated. But I'm just trying to
give you the big picture and keep our diagram a
little bit neater here by just kind of giving
you the big picture here. And so going back to
this particular reaction, it turns out that like
any reaction where we have to activate something,
with a higher energy functional group perhaps,
so to say, we need some input of chemical energy. And indeed this reaction is
coupled to the hydrolysis of ATP. And in fact, ATP, we
normally think of about it as ATP going to ADP in a
free phosphate group, but in this case, we
actually go all the way to a monophosphate group and
produce what we call a pyrophosphate group, which
is just two phosphate groups stacked together. And what really makes this
reaction thermodynamically favorable just kind of as a fun fact here, is that it turns out that when
this reacts with the water, it splits up into two
individual phosphate groups. And this hydrolysis reaction
right here ends up being having very negative delta G value. And so that's kind of what
drives this overall reaction forward. So just to summarize
here, we've successfully transformed our fatty acid
into an acyl-CoA group, which is what we refer to
as an activated fatty acid for the transport process
that we'll talk about next. But before we do that, I
do want to mention that the enzyme that catalyzes the reaction is actually located on this outer
mitochondrial membrane here and it's called acyl synthetase. So I kind of just think that
we're synthesizing essentially another acyl group, an
acyl-CoA, acyl synthetase. That's kind of how I
try and remember it by. Alright. So what happens to our
acyl-CoA molecule next? Well it turns out that
there is another molecule inside of the cell by
the name of carnitine, and at this usually has a kind
of bolty chemical structure to draw out. So I won't draw it out completely
but what I will draw out is the fact that it has
hydroxyl group here. And I'm drawing this hydroxyl group, this oxygen bound to hydrogen
because if I put on my organic chemistry hat for
a moment, I remind myself that this oxygen can
serve as a nucelophile, and form a bond with the carbon
on this acyl-CoA molecule like such. And the coenzyme A group
that we added can serve as a leaving group, and
the sulfur essentially can take back its electrons. And so ultimately, what
we've done is we've to this carnitine molecule,
which I'll abbreviate here, as just C now, for simplicity,
we've attached via this oxygen right here, our fatty acid. And so we have a structure
that looks something like this. Now just as a quick aside, one
way that I kind of remember the name of this molecule and
its function in fatty acid, oxidation is that I kind
of think about it as being carnivorous. Carnitine being carnivorous
for the fatty acid, so it kind of essentially
takes a bite into this acyl-CoA through its oxygen group
and is able to attach it to itself like this. So just a quick aside
in case that helps you remember anything. But going back to this
particular reaction, this reaction also has an
enzyme that carries this out, and it's called carnitine
acyl transferase. And it's located on, again,
the outer mitochondrial membrane. And so I'll go ahead and write that out. So carnitine acyl transferase. So pretty logical name, right? It's transferring the acyl
group onto the carnitine molecule. And it's actually denoted as
carnitine acyl transferase one because you will meet
another one of these enzymes on the inside of the mitochondrial
matrix in just a bit. So keep that at the back of your mind.