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Course: MCAT > Unit 6
Lesson 4: Eukaryotic cellsMitochondria
Uncover the intriguing details of mitochondria, known as the cell's powerhouse. Learn about their distinctive structure, including the outer and inner membranes, and their vital role in cellular respiration. Understand how these self-replicating organelles, equipped with their own genome, aid in ATP production and fuel the cell with energy.
Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Efrat Bruck.
Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Efrat Bruck.
Want to join the conversation?
- At the portion of video dealing with the electron transport chain, it is heavily stated that H+ cannot pass through the inner membrane without the use of ATP synthase. What is facilitating the physical movement of the H+ ions out into the intermembrane space?(20 votes)
- Every time the 2e- pass from one of the protein complexes to another, H+ ions are pushed into the intermembrane space by the energy produced from the 2e- moving down to a lower energy level.(6 votes)
- How does NADH produce two protons and two 2 electrons when oxidized? Where does the second hydrogen ion (proton) and electron come from?(9 votes)
- I may be wrong, but I believe she was incorrect when stating 2H are lost. NAD+ and H+ share 2 electrons in the reduced form (NADH) and those are the electrons freed during the oxidation to NAD+ and H+.(9 votes)
- Why is the Mitochondrial circular genome drawn in the inter-membrane space? It should be in the Matrix.(10 votes)
- At7:30, why can't the electrons go directly to the last enzyme (cytochrome reductase) and release a lot of energy in 1 time? Or do the electrons really need to jump from ezyme to enzyme?And if so, why?(3 votes)
- also, the analogy of gasoline powering an engine helps... Think of the electrons as a tank full of gasoline in a car. It contains a lot of potential energy to do quite a bit of work. However, if you were to release the energy all at once, not only would you blow the entire car up in one great wondrous explosion, it isn't a very effective use of that energy, as most of it would be going towards heat instead of work. It is better instead to use a little bit at a time, in controlled amounts. Likewise, the electrons passing down the ETC - discrete amounts of energy are used efficiently to drive work.(9 votes)
- Why is the inner membrane not permeable to small molecules?(4 votes)
- due to the presence of cardiolipin (which contains 4 fatty acid tails instead of the general 2 fatty acid tail structure found in bilayers).(5 votes)
- You stated the inner membrane of the mitochodria is impervious to even the smallest molecules. I'd like to know how pyruvate from the cytoplasm gets into the matrix to initiate the PDC pathway.(4 votes)
- Pyruvate enters the mitochondria through a membrane protein called pyruvate translocase!(4 votes)
- Quick question. When releasing the the electrons upon enzyme-hoping, wouldn't the hydrogen atoms become negatively charged since its releasing electrons?(2 votes)
- No, electrons have a negative charge;
Hydrogen atoms have 1 proton (positive charge) and 1 electron (negative charge), which gives them a neutral net charge (1p - 1e = 0).
In the "enzyme hopping", hydrogen atoms release electrons, meaning that they have 1 proton (positive charge) and 0 electrons (negative charge). As you can see there are more protons than electrons, meaning the net charge is now positive (1p - 0e = 1), thus the hydrogen atoms are positively charged.(3 votes)
- At0:38it is said mitochondria have an outer membrane. At1:14it is said mitochondria have an inner membrane. Where is the mitochondria-associated ER membrane (MAM) located? Also, at13:52it is said that mitochondria are self-replicating. Unfortunately, the method by which this happens (binary fission) is not mentioned. Lastly, if the mitochondria divides, what prevents the cell from becoming over-populated with these organelles?(2 votes)
- Is there a difference between the genome and genetic code?(2 votes)
- A genome is the genetic material of an organism. The genome includes both the genes (the coding regions) and the noncoding DNA, as well as mitochondrial DNA and chloroplast DNA.
The genetic code is the set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences) into proteins.
Source:
https://en.wikipedia.org/wiki/Genome
https://en.wikipedia.org/wiki/Genetic_code(0 votes)
- How many electrons are produced when FADH2 is oxidised ? is it 4 ?(1 vote)
- Both NADH and FADH2 provide only 2 electrons per molecule. It seems as if FADH2 --> FAD should produce 4 electrons as 2H are being lost, however, this is not the case. Good question.(2 votes)
Video transcript
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