Understanding Mitochondria: Structure, Function, and Importance
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Introduction
In today's detailed discussion, we will be exploring the fascinating world of mitochondria, often referred to as the "powerhouse of the cell." While many know they are crucial for producing ATP, there is so much more happening within these organelles. This article will break down the structure of mitochondria, delve into their various functions, and highlight the vital roles they play in cellular metabolism.
The Structure of Mitochondria
Mitochondria are unique organelles that have a distinct structure consisting of multiple components essential for their function.
Outer Membrane
The outer membrane of the mitochondria is characterized by its high permeability. It is composed of a phospholipid bilayer containing numerous large pore-forming proteins known as porins.
Key Features:
- High Permeability: Allows for free movement of small molecules and ions.
- Containment: Encases the organelle, protecting the inner workings.
Inner Membrane
In contrast to the outer membrane, the inner membrane is much less permeable and contains numerous transport proteins that regulate the entry and exit of substances.
Key Features:
- Low Permeability: Only allows specific molecules to pass through.
- Cristae Formation: The inner membrane is folded into structures called cristae, which increase surface area, accommodating various proteins and enzymes...
Intermembrane Space
The intermembrane space exists between the inner and outer membranes. This space is vital in processes such as the electron transport chain.
Mitochondrial Matrix
The interior of the mitochondria, known as the matrix, is filled with a fluid rich in enzymes, mitochondrial DNA (mtDNA), and ribosomes.
Summary of Structural Components:
- Outer Membrane - Permeable, encasing organelle.
- Inner Membrane - Less permeable with selective transport proteins.
- Intermembrane Space - Site of proton concentration for ATP generation.
- Mitochondrial Matrix - Contains mtDNA, enzymes, and ribosomes.
The Functions of Mitochondria
Mitochondria are pivotal not only for ATP production but also for various metabolic pathways. Let's delve deeper into their functions.
ATP Production
The primary function of mitochondria is to produce adenosine triphosphate (ATP) through a process known as oxidative phosphorylation, which occurs primarily at the inner membrane.
How ATP is Produced:
- Glycolysis: Glucose is broken down into pyruvate.
- Krebs Cycle: Pyruvate is converted into acetyl-CoA and enters the Krebs cycle, yielding electron carriers NADH and FADH2.
- Electron Transport Chain (ETC): These carriers donate electrons to the ETC, leading to proton pumping into the intermembrane space.
- ATP Synthase Mechanism: Protons flow back through ATP synthase, providing energy to convert ADP and inorganic phosphate into ATP.
Role in Metabolism
Mitochondria are involved in multiple metabolic pathways, including:
- Krebs Cycle: Generates high-energy electron carriers from acetyl-CoA.
- Beta Oxidation: Fatty acids are broken down to produce acetyl-CoA.
- Urea Cycle: Converts toxic ammonia to urea for excretion.
- Gluconeogenesis: Converts non-carbohydrates into glucose, utilizing substrates from other pathways.
Protein Transport
Mitochondria do not synthesize all proteins they need. Instead, unfolded proteins synthesized in the cytoplasm are imported. They are facilitated by:
- Translocase of Outer Membrane (TOM): Helps transport proteins into the intermembrane space.
- Translocase of Inner Membrane (TIM): Assists in moving proteins into the mitochondrial matrix.
- Chaperone Proteins: Assist in the proper folding of imported proteins.
Mitochondrial DNA (mtDNA)
Mitochondria possess their DNA, which is important for encoding a small number of essential proteins for mitochondrial function. This mtDNA is inherited maternally and can replicate independently within the organelle.
Apoptosis and Mitochondrial Role
Mitochondria play a critical role in apoptosis, or programmed cell death. Key proteins like cytochrome c released during certain cellular stress signals activate apoptotic pathways, ensuring that damaged or infected cells undergo controlled death to maintain overall health.
Conclusion
In summary, mitochondria are dynamic organelles with diverse functions crucial for cellular health and energy production. Understanding their structure—from the outer membrane to the mitochondrial matrix—and the various metabolic functions allows us to appreciate their role in significant life processes. Mitochondria not only generate energy but also regulate metabolic reactions, assist in cellular signaling, and contribute to apoptosis. Continuing to explore these organelles could lead to vital insights in health and disease management.
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the structure and function of the mitochondria before we get started if you guys like this video makes sense
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below take you to our website where you guys can check those out all right mitochondria it's always referred to as
the PowerHouse of the cell right we're going to dig a little bit deeper okay so when we talk about the mitochondria
let's first go through the structural components of it and then what we'll do is we'll dig into the function of it
step by step kind of not just sticking with the only factors that it produces ATP there are a
lot of things that this son of a gun can do all right so the mitochondria first thing is it's really kind of I'm not
even kidding this is the way that they hold in the textbook a sausage shaped uh kind of like organelle inside of the
cell and when we look at it and actually zoom in on the structure there's a couple different components that we have
to know the first one is that you have this kind of like membrane and it's double layered it has like a outer
membrane out here so this is called your outer membrane and again it's made up of a like a phospholipid layer bilayer
actually Auto outer membrane big thing that I kind of want you to take away from the outer membrane
is the outer membrane is a very permeable membrane okay so it's a very very permeable membrane highly highly
permeable so it's got these big pouring molecules that allow for things to move in and out of the mitochondria one big
thing that you may see on your exam all right so here's the outer membrane then if you look here's the other
component of it right here you see how we have the outer membrane which is this kind of maroon line and then here we
membrane again another phospholipid bilayer which is pretty cool big thing to take away from this one though is it
is not very permeable has a lot of selective proteins Transporters that are present on it that really are very
closely regulated and determine what moves in and out of the mitochondria so this one is less permeable really kind
of a big just term that I want you guys to take away from these two now there's a space
and that exists right between these two so here was the outer here was the enter there's a little space between these two
is really really highly concentrated with proton ions which is really really helpful with your electron transport
chain so we'll get into that a little bit later all right so we got outer membrane inner
membrane inter membrane space which is kind of just a little bit of fluid rich in protons okay
we come into the inner part here so one more thing you see how they have the inner membrane if we were to follow this
thing along look how it kind of continues continues and then you get like these like little invaginations
that are coming off of the inner membrane that's a really really important thing so what I want to add on
here is with the inner membrane so with the inner membrane so with the inner membrane we're going
to rewrite it there is a specific type so this kind of invagination is actually called the Christa so it's a
continuation of the inner membrane but invaginates into the center it's all these things here's a Chris Day here's a
Christa here's a Chris Day Chris Day Chris Day Chris day okay the whole purpose of these puppies is to increase
the surface area for a lot of specific types of metabolic reactions that we'll talk about a little bit later okay
so we got outer membrane inner membrane intermembrane space the inner membrane there's a special type of them which
invaginates into the actual center of the mitochondria called the Christa which increases the surface area for a
lot of metabolic reactions the last part is all of this kind of white space here which is basically the
mitochondrial Matrix so really all of this in here is called your mitochondrial Matrix and it has a bunch
of different fluid and solutes in it but two particular things that are really pertinent to The Matrix
um the major the mitochondrial Matrix is what's called mitochondrial DNA which is represented right here see these little
guys right there that's your mitochondrial DNA it's really cool because this is actually maternal DNA so
obviously has some types of genes to uncode to make particular RNA to make proteins but we need certain things that
to be able to translate that RNA and make proteins and some of these proteins the mitochondria can make
on its own to help with its own functions so that's a really really cool thing and we'll get into that a little
bit later but this is the big big thing that I want you to understand so again to recap it this is outer membrane this
is inner membrane a special invagination of the inner membrane into the center is called the crestae which one's highly
permeable outer which one's less permeable inner what's the space between the outer and the inner membrane the
inner membrane space what is it rich in proton ions and then what is all of this fluid here that is in the center of the
mitochondria the mitochondrial Matrix rich in mitochondrial DNA and ribosomes the mitochondrion is an organelle that
respiration the mitochondria make ATP molecules that provide the energy for all of the cell's activities
cells that need more energy have more mitochondria let's now dig into the function of the
mitochondria specifically what I want to talk about is the membranes so we'll get into the Matrix that's next but what I
want to talk about first is let's talk a little bit about the outer and the inner membrane and what are some of the
functions that this puppy does so let's come down here the first thing that I want to discuss here is it plays
a huge role in protein transport the membranes so what we're doing is we're zooming in this is a cell
mitochondria so I'm going to represent this as the outer membrane the inter membrane space and the inner membrane
and then what would this be this would be the Matrix so I'm just zooming in onto the part of the
DNA here's like some of that mitochondrial DNA and it can make RNA which can helpful to make some proteins
but it doesn't make all the proteins that it needs to be able to function and so sometimes we have to take some of the
proteins from the nucleus so the nucleus will help us to make RNA RNA will then make proteins
and these proteins have to get sent into the mitochondria and that's really really important
so for example here here's our DNA it's going to make mRNA m r and a that mRNA will then come out
via the nuclear pores when it comes out via the nuclear pores here's my mRNA it'll then combine with
ribosomes and from this from the ribosomes will then synthesize what proteins but here's the big thing these
proteins are unfolded oh there we go it's unfolded therefore it's not Super Active it's not the
moving these unfolded proteins that it needs to be able to perform reactions inside of this the mitochondria it needs
to transport it across so what happens is this protein here will get chaperoned and then we'll bind
onto this like little receptor here and there is this outer membrane translocase we literally call them Toms translocase
of the outer membrane and what happens is once this unfolded protein binds to the receptor what it'll
do is it'll open up this Tom and move this unfolded protein into the inter membrane space
and the inter membrane space a little chaperone protein will bind to it and bring it to this next point so it'll
bring it to this next receptor on the inner membrane when it binds here it activates this particular stimulated
this receptor stimulated this receptor when it stimulates this receptor it opens up this next channel on the inner
membrane this is called Tim I'm not even kidding so translocase of the inner membrane and when that binds onto the
mitochondrial Matrix we need maybe this protein to perform specific things maybe it's an enzyme that plays a role in a
types of proteases or other enzymes that will then work on this protein and properly fold him
together and activate him and make him into a specific special enzyme and now this is a active
folded enzyme and it's ready for it to perform its functions inside of the mitochondria
and there's so many different proteins that you need and so it's a really really important point because the
mitochondrial DNA right the mitochondrial DNA it only makes like 15 of the proteins so really when it goes
to make proteins these proteins that it makes is only 15 of what's needed so that means I need a lot of proteins from
the nucleus to help me to perform a lot of the functions so that's one of the cool things the mitochondria accepts
proteins and they're unfolded form brings them into them and then activates them by folding them properly and then
uses those for their metabolic reactions pretty cool right all right that's one of the functions of
the membrane let's go on to another one which is a plays a role in like miscellaneous transport and then we'll
talk about the Big Mac Daddy function of the mitochondria that the membrane plays a role in and that is the electron
transport chain all right my friend so now next one is it also plays a role so with protein transport is a big one but
it plays our own like small miscellaneous things and this may seem like very like straightforward and I I
kind of thought that was common sense it is but it's just a quick reminder of things that also a lot of things move
across the mitochondrial membrane right and what are those things well I want you to understand and we're going to get
into them a little bit but metabolic reactions they're very very heavily involved in the the mitochondria and so
in order for some of these metabolic reactions to occur I have to move things like carbohydrates
right across the actual what across the mitochondrial membrane these have to move in and out
because you'll talk later that we do a lot of different things like glycolysis has to occur inside of the mitochondrial
we have to move things like fatty acids so we move things like fatty acids in here as well because they play a role in
something that we'll talk about later called beta oxidation right we have to move things like amino acids in here
right because they may play a role in something called the urea cycle and so there's a lot of different things that
are actually moving across this cell membrane and that's a really really important point that there's a lot of
ions that are moving across ions and small macromolecules that are moving across the mitochondrial membrane very
very key and again I think one of the big things to understand here is if they were to ask you a question regarding the
transport of things across the mitochondrial membrane which of the membranes is very permeable outer and
to understand that is very critical to the function of the mitochondria and oftentimes what it's referred to with
that big buzzword term is the PowerHouse of the cell produces ATP ATP is power energy right so this electron transport
chain is huge and it's found primarily on the inner membrane so you don't really see this involved in the outer
membrane primarily in our membrane and we're not going to go into crazy detail of all the different processes
that are occurring on the electronic transport chain we're going to talk about that in the biochemistry or
metabolism playlist if you guys want to go watch that we have a playlist where we go through the electron
transportation in depth and we do an overview of it but the basic concept here is that you have these protein
molecules and they make up these different complexes like complex one complex two complex three complex four
is that they take things you know you have your Krebs cycle and so from your Krebs cycle you take a molecule called
and then acetyl-coa goes through this special thing called the Krebs cycle so this is called your Krebs cycle
and from the Krebs cycle which occurs in the mitochondria we form these high energy electron Transporters called
fadh2 and nadhs and they're carrying with them a lot of electrons in the form of like they have them in a hydrogen
what's called a hydride ion and what they do is they take and they transport these electrons onto these proteins and
they drop the electrons off in them and then these guys pass these electrons down the chain from areas of high energy
to areas of low energy and what that does is with each time that that happens it pumps all these protons out into the
reason it's protons and then these protons what they do is they move from areas of in this
situation they move down this ATP synthase and they move down pretty powerfully and what it does is is it
moves down this ATP synthase it creates this energy that the protein can Harvest and when it harvests all that energy
and an inorganic phosphate they're kind of stuck to this this ATP synthase but as the protons run down this gradient as
electrons are being passed down it creates this energy that fuses these puppies together and then what it does
is it releases it in the form of ATP and this process where we make ATP via the electron transport chain is a very
specific type and we call this type of ATP production oxidative phosphorylation phosphorylation so a
one side effect though that comes from these reactions is that all these electrons that are getting passed along
they can actually combine with things like oxygen and they can combine with other molecules and they can make things
like hydrogen peroxide or they can make superoxide free radicals so they basically can increase the formation of
things called reactive oxygen species which is that unfortunate side reaction from the electron transport chain that's
three functions to take away from the inner and outer membrane outer membrane highly permeable inner membrane less
permeable they allow for miscellaneous things to travel in and out of the mitochondria specifically for metabolic
reactions things like carbohydrates things like amino acids things like fatty acids and we'll talk about those
reactions in a second they also allow for unfolded proteins that are made by the nucleus by
ribosomes in the cytoplasm to be transported into the mitochondria so that they can use them for their
functions they don't make all the proteins that they need they really only make like 15 of the proteins and enzymes
that they need so they need a lot of proteins from from the actual nucleus and the last thing is they have the
electron transport chain specifically on the inner membrane and what does it do it takes high energy electrons from
nadhs fadh2s which are generated from metabolic reactions passes it on to those things they pass the electrons
down this chain and pump protons into the inter membrane space and then allows for it to flow back down into the
unfortunate side reaction that can occur from the electron transport chain is you can make reactive oxygen species
detail of what are these reactions that occur in the mitochondrial Matrix we've like clipped off a few of these like
okay there's you know the Krebs cycle there's gluconeogenesis I already said those terms there's the urea cycle
there's fatty acid oxidation some of these things that I've said we're going to kind of quickly go over them and talk
about how they're involved particularly in the mitochondrial Matrix so that if you're asked which of the following
reactions occur in the mitochondrial Matrix and you'll see this when we get into biochemistry you can pick out which
one it is likely that's going to be occurring there all right and then we'll briefly talk finishing about
mitochondrial DNA and we'll talk about ribosomes let's get over there and talk about that all right guys so now we're
going to talk about the next component here which is the functions involved in the mitochondrial Matrix so we went over
the inner membrane and outer membrane how they're particularly involved in things like protein transport
miscellaneous transport of things like nutrients as well as some ions and on top of that we went over the electron on
transport chain a really really big function for ATP production via oxidative phosphorylation
well the Matrix really what's cool about this is that we already kind of gave a little leeway or
kind of like introduced this slightly that there's a lot of metabolic reactions that can occur in the
mitochondria so really what I'm looking at inside of this red membrane here can pretend that this is the combination of
the inner outer membrane and the inter membrane space this is just the entire mitochondrial membrane here and then in
this is going to be your mitochondrial Matrix and that here is going to be your cytoplasm inside of the cell so this is
all cell but we're just zooming in on the mitochondria particularly The Matrix inside there and then the cytoplasm all
like glucose so you bring glucose into the cell right so let's say that you bring glucose into the cell what we know
is that once glucose gets into the cell it eventually gets converted into something called pyruvate via glycolysis
and then that pyruvate will get brought in to the actual mitochondria when pyruvate is brought into the
and then acetyl-coa will go through these series of like steps which I don't want to talk about every single
substrate we'll do that later in Biochemistry but this process where it goes through this cycle is called the
here so far one is you're seeing the conversion of pyruvate into acetyl COA and the second thing you're seeing is
the Krebs cycle and we already briefly talked that coming off of the Krebs cycle is those high energy molecules
that carry electrons called nadhn fadh2 and these go to the electron transport chain where they pass off
those electrons pump protons into the inter membrane space and they help to generate something called ATP via
oxidative phosphorylation well what's another reaction that can occur here there's another cool one you
know whenever we take something like fatty acids so fatty acids these are just long chains like sometimes these
suckers can be like 16 carbons long we can bring these in to the mitochondrial Matrix across the membrane
so that's another example of Transport across that and then they can go through these series of metabolic reactions
this step here is called beta oxidation this is another one of the reactions that takes place inside of the
mitochondria Matrix so so far we have the conversion of pyruvate into acetyl COA the Krebs cycle and then beta
you know when you take something like amino acids amino acids can get brought into the mitochondria as well
and what happens is amino acids eventually they can get metabolized into something called ammonia right so they
can actually get metabolized and when they get metabolized they give way to products in the Krebs cycle we're not
going to mention which ones but when it does do that it can give off something called ammonia
and ammonia is really really toxic really nasty son of a gun that you don't want to have to deal with
and it's called the urea cycle and what happens is it liberates this molecule called urea Which is less toxic in
comparison to the ammonia and it's easier to be excreted but this cycle here this cycle that occurs kind of in
the What specifically in the mitochondrion even a little bit if you notice over here even a little bit of
the cytoplasm What's this called This is called the urea cycle so this is called the urea
can take something like amino acids I can take something like odd chain fatty acids and I can convert them into
specific substrates but then what I can do which I'm going to represent here with a let's do it with a pink Arrow
is I can convert them back into pyruvate and then back into glucose you know what this is called when you
take something like an amino acid and not chain fatty acids and make glucose from it it's called gluconeogenesis
so that's another reaction which I'm going to represent kind of going in this with the Pink Arrow so I'll represent it
right here as the fifth reaction this is called gluconeogenesis okay so that's another one and then
there's one more reaction from the Krebs cycle you can take some of these intermediates
and make something called heme and some of these molecules of heme are actually synthesized in two
something called heme there's another reaction so what's that one that's the sixth one so what I'm trying to tell you
here is there are so many metabolic reactions that take place within the mitochondrial Matrix what are some of
them if we were to again recap them we call these reactions first one is pyruvate to acetyl-coa
that's one particular reaction the second one that is also really important here is the Krebs cycle
also occurs is going to be and I actually made it a two but that should be a three I apologize this is beta
oxidation so this is breaking down fatty acids so the third one should be beta oxidation of fatty acids so we'll put
so we go three we go four this is the urea cycle so this is the urea cycle but another big thing that I want to add
on here is that urea cycle can occur in two places as you're noticing by this reaction it
another particular reactions beside this one as we go to Five is this involved in what's called gluconeogenesis
this is called gluco neogenesis and what is gluconeogenesis it's taking something like amino acids
or taking something like odd chain fatty acids and converting them back into glucose but did you notice that this one
also takes place in the mitochondria and it also takes place in the cytoplasm another particular reaction is taking
something like Krebs cycle intermediates and making heme and it's involved in two particular places where it's involved in
the mitochondria and in the cytoplasm so that's another particular reaction which is heme synthesis
combo I remember hug heme synthesis urea cycle and gluconeogenesis as a little mnemonic there is technically one last
one if you really wanted to remember I could take acetyl coase and I could shunt them into making something called
so you can see there is a lot of metabolic reactions that take place inside of the mitochondria a massive
amount it's insane I don't expect you to remember every single one of these steps here the big thing I want you to
understand is that the mitochondria is involved in a ton of metabolic reactions that if you try and remember this now
it'll be helpful whenever we get into biochemistry and you'll see a lot of these reactions take place over and over
and over again that we'll go over all right so this is the big thing I want you to take away from this aspect
of the mitochondrial Matrix let's come down and talk about a couple more things with the mitochondria
so so far we got protein transport miscellaneous transport electron transport chain we got a lot of
metabolic reactions seven of them with three of them hug hug heme synthesis urea cycle and gluconeogenesis occurring
in both the mitochondria and cytoplasm the last thing is that this son of a gun can be involved in apoptosis it's
actually pretty crazy I'm not going to go too crazy with this we'll talk about a more detailed cell pathology but
whenever there's some type of process where a cell is infected or is cancerous or it needs to die unfortunately it has
to die there's special molecules present called cytochrome C and it's located inside of the mitochondrial Matrix
now naturally we don't want these things to be leaking out so there's proteins called like bcl2
decrease the number of these and so now we can't control these cytochrome molecules from leaking out
and the cytochrome C molecules which is supposed to be kept in the mitochondrial Matrix leaks out
start ripping through a bunch of different cells and so they start just damaging cell membrane damaging
organelles and eventually cause the cell to undergo its death process okay so it'll lead to a lot of signaling process
that will trigger it's programmed cell death that's what apoptosis is it's programmed
mitochondria and that's pertaining to the DNA and the ribosomes what do they really do it's not too hard to
understand it's that here's our mitochondrial DNA with this I could do two things with it one is I can make
more of it what's that called DNA replication this could be important if I want to take maybe and replicate my
actual mitochondria so if I want to take this mitochondria and maybe undergo what's called a fission process and make
two of these puppies here let's say that I wanted to make two of these mitochondria I would want them both to
contain an equal amount of mitochondrial DNA you know what's super interesting believe it or not so
fission is a process where bacteria prokaryotic cells undergo division there's a theory
um back in the day called well it's still there it's called the endosymbiotic theory
the mitochondria back in the day used to just be a bacterial cell a prokaryote and it would have its own DNA and then
what happened is it got engulfed by a eukaryotic cell and then when it got engulfed inside of the eukaryotic cell
it then became something called a mitochondria and so it kind of started down regulating a lot of its genes and
proteins and stuff like that and the nucleus of a eukaryotic cell became the new Factory of DNA and it has it
cytoplasm to make many of the proteins that are needed and the mitochondria just primarily kind of got downgraded to
producing ATP and having some metabolic reactions occur in it so that's something called the endosymbiotic
theory but that's a really cool concept that basically the mitochondria used to be something called prokaryotic cells
and they just got engulfed by eukaryotic cells and they got downgraded to becoming a mitochondria which is kind of
interesting but that's one thing is we can kind of replicate them to make more of these types of mitochondria via
process called fission the other concept here is that we can take this mitochondrial DNA and undergo
transcription and we undergo transcription this makes something called RNA and these RNA molecules
combined with the ribosomes located in the mitochondria and here's another important Point these ribosomes are
called 70s ribosomes you know what they are in the the cytoplasm of eukaryotic cells which we'll talk about soon
they're ads that's another question they could potentially ask you so watch out for that but from this mitochondrial DNA
can replicate to undergo division of the mitochondria or it can make RNA and that's really important because you need
the DNA to make RNA you need the RNA to be translated and the translation process will then synthesize
particular types of proteins and these proteins that it makes generally accounts for about 15 percent of the
proteins that are needed for the mitochondria to be able to perform its functions so that means it needs a
decent chunk about 85 of the proteins to come from the nuclear DNA nuclear RNA than to get translated by the cytosolic
ribosomes and they get transported across the mitochondrial membrane so that it has those functions that's a
really cool concept and my friends that finishes off our discussion on the mitochondria their structure their
function I hope it made sense I hope that you guys take again the step-by-step process we go through the
inner outer membrane we went through the inter membrane space talked about their involves in protein transport the
electron transport chain and the miscellaneous transport and then we dug into the Matrix a little bit and then we
talked a little bit about how the mitochondrial DNA are involved in replicating itself for the actual
mitochondria to divide or making proteins via transcription translating those by ribosomes in them 70s ribosomes
to make proteins for it to function we also talked about all the metabolic reactions that are plentiful and
occurring inside of the mitochondria Matrix I hope it made sense and as always the engineers until next time