mitochondria are organelles that are found in cells and they are responsible
for producing ATP or adenosine triphosphate ATP is a molecule that
serves as a principal source of energy for cells and for this reason
mitochondria are known as the powerhouse of the cell because they provide the
cell with power or energy so here's a picture of a mitochondria that was kind
of sliced down the middle and let's take a look at its structure so it has an
outer membrane and the outer membrane is made up of a lipid bilayer and you might
recognize that term as describing the Summa random cell and this lipid bilayer
is not permeable to most things but it is permeable to very small molecules and
that's because it has certain proteins embedded in it that allow small
molecules to pass the mitochondria also has an inner membrane as you can see and
the inner membrane is also made up of a lipid bilayer but it is not permeable to
small molecules and you'll see in a few moments why this is an important fact to
keep in mind and you may have noticed that the inner membrane is not smooth in
the way that the outer membrane is but rather it has many folds and these folds
are known as well individually each fold is a crista and plurally call them
Christy and the reason that the inner membrane is folded into these Christy is
because on the inner membrane there are lots of different proteins that are
necessary for cellular respiration and by folding the membrane we just increase
the surface area and allow a greater amount of membrane to be in a smaller
space so it basically just gives us more room to work with the enzymes
and more room for cellular respiration to happen and this space between the
outer and inner membrane is known as the inter membrane space I'm going to write
it over here on the side and then the center of the mitochondria we call that
the matrix so now that we've discussed the structure of mitochondria let's
let's see how that relates to cellular respiration and what happens here let's
go through the steps of cellular respiration which is the process by
which we make ATP and then let's see how it relates to the mitochondria so the
first step of cellular respiration is glycolysis and what happens during
glycolysis is the molecule glucose which is a six carbon molecule gets split into
two molecules of pyruvate pyruvate is a three carbon molecule Anglet calluses
actually does not happen in the mitochondria it's the only step of
cellular respiration that happens in the cytoplasm the next step of cellular
respiration is what's known as the PDC or the pyruvate dehydrogenase complex
and what happens during the PDC is that pyruvate and remember we have two of
them gets converted to a molecule knows known as acetyl co a and you may
recognize acetyl co as the molecule that enters the Krebs cycle and the PDC
happens in the matrix of the mitochondria so all the enzymes that are
involved in the PC are found in the matrix of course as well the next step
of cellular respiration is the Krebs cycle and in the Krebs cycle acetyl co a
is going to undergo a series of reactions which I'm not going to go into
the details of that right now and this happens also in the matrix of
the mitochondria and what I'm going to focus on right now is that at the end of
the Krebs cycle we produce two molecules
nadh and fadh2 and these are electron carriers you'll see in a moment why
they're so important and the last step of some of the respiration is the
electron transport chain the electron transport chain happens on the inner
mitochondrial membrane so on the membrane itself and this is the part we
were actually going to make ATP with the help of these electron carriers that we
made during the Krebs cycle so let's take a closer look at the inner
mitochondrial membrane and see what happens during the electron transport
chain so here's a more close-up diagram of the
inner mitochondrial membrane let's just orient ourselves let's say that over
here is the outer membrane which would make this area over here the cytoplasm
of the cell and let's say that over here is the matrix of the mitochondria
and here justly what is the inner membrane so you can see the inner
membrane is studded with a bunch of these enzymes and these are the enzymes
that are involved in the electron transport chain and in case you want to
know the names of these various enzymes there over here some of them are pretty
long so we're just going to refer to them by numbers this one over here is
going to be one that's NADH reductase then this white one that's cytochrome Q
this green one is succinate dehydrogenase then we have number three
I'm not going to mention the names you can read them if you want then we have
cytochrome C over here and then there's number four right over here so we have
nadh and fadh2 which were produced during the krebs cycle and these are our
electron carriers and I'm going to describe what happens to NADH but the
same thing happens to fadh2 so any D H is going to be oxidized or lose
electrons so let's write out that reaction NADH will turn into nad plus
plus two hydrogen ions plus two electrons so it got reduced and those
two like I'm sorry it got oxidized it lost electrons those two electrons are
going to go onto enzyme number one so while NADH lost electrons and got
oxidized the first enzyme gained electrons or it got reduced but enzyme
one is not going to hold on to the electrons it's going to pass them on to
the next enzyme which is cytochrome Q so now enzyme number 1s oxidized because it
loses electrons but enzyme cytochrome Q gets reduced because it gains electrons
and then the same thing will happen with the next enzyme cytochrome Q will pass
those two electrons on to the next enzyme and in case you're wondering
where this sign enzyme two comes in so fadh2 when it gets oxidized its
electrons go directly to enzyme two from there to cytochrome Q from there to
three etc but anyways back to what's happening
to our NADH so the two electrons are an enzyme 3 then they go to cytochrome C
then they go to enzyme 4 and then finally those two electrons are used to
reduce oxygen and make water so I'm going to write 1/2 co2 which is the same
as one oxygen atom plus 2 H pluses plus those two electrons give us water 2 h
plus is plus 2 electrons that's the same thing as saying 2 H so we produce water
let's go back to the electrons jumping from one enzyme to the next when these
electrons go from one enzyme to the next they're going from a state of higher
energy to a state of lower energy and when electrons go from a state of higher
energy toastie of lower energy they release energy so I'm just going to
write energy kind of coming out of that out of those arrows and that energy is
used for something the enzymes in the inner mitochondrial membrane use that
energy to do something they use that energy to pump hydrogen ions out from
the matrix and into the intermembrane space if you recall the inter membrane
space is the space between the inner and outer mitochondrial membrane so we're
going to have at the end of this process a whole bunch of hydrogen ions in this
inter membrane space and that makes the inter membrane space more acidic sorry
not not out there right the outer membrane let's just to make things clear
so we're talking about the inter membrane space so the inter membrane
space now becomes acidic
while the matrix becomes basic and we know that in general molecules like to
go from areas of high concentration to areas of low concentration and this
inter membrane space has so many high hydrogen ions and they just want to get
back into the matrix but if you recall we said that the inner membrane is not
permeable even to the tiniest molecules so the H+ ions cannot go through the
inner membrane there's only one thing that they can get back into the matrix
and that is they can go through this special enzyme known as ATP synthase ATP
synthase has special channels in it that will allow H+ ions to pass through so
the H+ ions will pass through these special channels in ATP synthase and
when they do they're going to cause this axle to turn let's focus now on the
bottom part of ATP synthase it has this part of the protein has EDPs adenosine
diphosphate and peas or phosphates there are a lot of them are just going to
drill one of each and when the axle spins as the H+ ions go through it's
going to cause the ADP zenpeace kind of knock into each other and attach so ATP
will attach to P and we're finally going to produce ATP the molecule that were
trying to get to this entire time
let's just mention two terms that are relevant here the first is chemiosmosis
chemiosmosis refers to the hydrogen ions passing through the special channels in
ATP synthase and then spinning the axle and making ATP and another term you
should know is oxidative phosphorylation
oxidative phosphorylation while phosphorylation tells if something's
being phosphorylated so we're referring to adp being phosphorylated or adding a
pea to it and we're making ATP and the term oxidative tells us that the
phosphorylation is happening because of oxidation because of the oxidation of
NADH and subsequently the oxidation of all these enzymes let's just recap
everything that happened here we had nadh and fadh2 which were
produced during the krebs cycle they got oxidized they lost electrons
those electrons went on to the first enzyme and from there on they went from
enzyme to enzyme to enzyme and when those electrons went from enzyme to
enzyme they went from a state of higher energy to a state of lower energy when
electrons do that they release energy that energy was used to pump hydrogen
ions from the matrix into the intermembrane space so we have a bunch
of G's of these hydrogen ions in the intermembrane space these hydrogen ions
want to get back because there's a high concentration in the intermembrane space
on low concentration in matrix but as we explain the inner membrane is not
permeable to h+ ions so the only way for them to get back is to go through ETP
synthase through the special channels in ATP synthase when they go through they
spin the axle that causes this part of the protein to knock ADP and P together
and that finally produces ATP and that ATP then provides the cell with the
energy that it needs there is one more topic about mitochondria that I'd like
to discuss and that is that mitochondria have their own genome so they have one
piece of circular DNA it's a lot smaller than the amount of DNA that's found in
the nucleus but it allows them to do a lot of things in there
own mitochondria are also self-replicating so they can replicate
independently of the cell in which they are and because they have their own
genome they're able to make their own ribosomal RNA tRNA that's transfer RNA
they actually make some of the proteins involved in the electron transport chain
I'm just going to abbreviate that etc' so DDT stands for electron transport
chain and they also produce parts of the protein ATP synthase it's a rather
complex protein and they do produce some parts of it however most of the proteins
of the mitochondria are actually encoded for by the nuclear genome the
mitochondria even uses a different system of transcription and translation
and when I say different I mean different than the nuclear genes and
mitochondria even has its own unique genetic code so mitochondria are
relatively independent organelles