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Course: MCAT > Unit 5
Lesson 15: Krebs (citric acid) cycle and oxidative phosphorylation- Krebs (citric acid) cycle and oxidative phosphorylation questions
- Oxidative phosphorylation questions
- The citric acid cycle
- Krebs / citric acid cycle
- Regulation of pyruvate dehydrogenase
- Regulation of Krebs-TCA cycle
- Electron transport chain
- Oxidative Phosphorylation: The major energy provider of the cell
- Oxidative phosphorylation and chemiosmosis
- Regulation of oxidative phosphorylation
- Mitochondria, apoptosis, and oxidative stress
- Calculating ATP produced in cellular respiration
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Oxidative phosphorylation and chemiosmosis
Oxidative phosphorylation is a vital cellular respiration process that generates ATP. It involves the oxidation of NADH and FADH2 and phosphorylation. The process creates a hydrogen gradient, enabling chemiosmosis and ATP synthesis. This energy conversion is essential for all life forms, from bacteria to sharks. Created by Sal Khan.
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- Please enlighten me on NADH and FADH. I searched the 8 lectures for an explanation to no avail.(9 votes)
- Both are electron carriers, which just means they store electrons at a relatively high energy state. These electrons can be used to power other reactions, when they go to a lower energy state and release energy for use in the reaction.(4 votes)
- If phosphorylation can happen directly without oxidation (substrate phosphorylation) then why is there oxidative phosphorylation at all? Why not just use substrate phosphorylation all the time?(6 votes)
- Substrate phosphorylation is not used all the time because it cannot produce ATP from NADH and FADH2, whereas oxidative phosphorylation can. Because of this, more ATP can be produced from a single glucose molecule, making cellular respiration more efficient.(9 votes)
- I've been wondering about this for a while, because in the textbooks and these videos continuously NADH is "named" as the e- carrier, but the diagrams that will be used on our exam (it's officialized so we recognize them) keep saying NADH2 being passed around. So, I'm getting quite confused what the difference is, and why one say NADH while the other says NADH2. Does anyone know?(4 votes)
- There is NADH, and then there is FADH2. NADH is the "electron carrier" because it picks up electrons from things in glycolysis and the Krebs Cycle, and gives those electrons to the electron transport chain, so that they can be used to make Energy / ATP. If you see NADH2 written, you can just consider it to mean NADH (but if you know they want you to write NADH2 on the test I would still say go for that - just make sure to not confuse it for FADH2)
NADH2 is sometimes used because technically the reduction of NAD+ is [2H and NAD+] --> [NADH and H+] , but really, it is only the NADH of those products that is actually interacting with the electron transport chain.(5 votes)
- I can't understand what are electron carriers . Can you please tell me ?(3 votes)
- Any of various molecules that are capable of accepting one or two electrons from one molecule and donating them to another in the process of electron transport. As the electrons are transferred from one electron carrier to another, their energy level decreases, and energy is released. Cytochromes and quinones (such as coenzyme Q) are some examples of electron carriers.(7 votes)
- Can you make a video on substrate level phosphorylation ?(3 votes)
- Glycolysis is substrate level, so technically he made it already. Even in the TCA cycle.(3 votes)
- whats the difference between oxidative phosphorylation and substrate phosphorylation? also regarding the electron transport chain, is cytochrome Q the only complex (out of the 4, not including ATP synthase) that doesn't pump hydrogen atoms to the inner membrane space? please get back to me i have an exam on tuesday!(3 votes)
- atp directly synthesised during substrate oxidation is called substrate level phosphorylation..whereas oxidative phosphorylation is linked with mitochondrial electron transport chain..(2 votes)
- What is a coupled reaction and why is oxidative phosphorylation considered a coupled reaction?(3 votes)
- A coupled reaction is one where the free energy of a thermodynamically favorable reaction (such as the hydrolysis of ATP) is used to drive a thermodynamically unfavorable reaction by coupling or 'mechanistically joining' the two reactions.
The most important coupled reaction occurs in oxidative phosphorylation that occur during respiration (i.e. that which occurs beween oxidation of fuels and synthesis of ATP by ATP synthetase).
In the chemiosmotic theory of oxidative phosphorylation, electron transport via the respiratory chain to molecular oxygen creates a proton gradient across the inner mitochondrial membrane (which is normally impermeable to protons). Protons are pumped outwards. This proton gradient, or protonmotive force, may be used to 'drive' the formation of ADP to ATP (thermodynamically unfavorable) reaction to the right, via the ATP synthetase complex.
Source: http://biology.stackexchange.com/questions/2051/what-is-a-coupled-reaction-and-why-do-cells-couple-reactions(2 votes)
- Can someone please explain Chemiosmosis? I don’t really understand how it works with the atp synthase? Thank you!(3 votes)
- What is the difference between Chemiosmosis and ETC(3 votes)
- Wouldn't the water equation be that O2+4e-+4H+-->2H2O ?(2 votes)
- Yes, but in this video he wanted to focus on the production of just one water molecule, that´s why he used 1/2 O2 intead of just using whole numbers. So you´re right, your equation is the balanced equation we would normally use.(2 votes)
Video transcript
I made a slight error
in the electron transport chain video. And I just wanted to correct
it in this one. And it's also an opportunity for
me to include a little bit of terminology that I forgot
to include in that video. So when I described the electron
transport chain, you remember, it's just you have
some high-energy electrons in NADH and they get transferred
from one molecule to another. And as they get transferred
they go into lower energy states and they release
energy. And then the final electron
acceptor was oxygen. Oxygen got reduced right here. But if you look at both sides of
this equation, the mistake was, I need two hydrogens. If I have two hydrogens on the
right-hand side of the water, I need two hydrogens on
the left-hand side. So there should be
a 2 right there. So that was what I would
consider to be a minor mistake in the last video. But this also gives me a chance
to introduce you to some more terminology. So this whole process, we know
that this is called oxidation. When NADH loses a hydrogen. Remember oxidation is losing,
formally electrons. But when it loses the hydrogen,
it loses the opportunity to hog that
hydrogen's electrons. So this whole process of the
electron transport chain is one molecule after another
getting oxidized until you have a final electron
acceptor in water. So this is-- obviously you could
call this oxidation. You know, just very generally. And then the second part of the
electron transport chain-- or maybe we shouldn't even call
this part of the electron transport chain-- the
process where the ATP is actually formed. The adding of a phosphate group
to another molecule is called phosphorylation. So the whole process of creating
ATP through the electron transport chain. Remember the electron transport
chain releases energy that creates this
hydrogen gradient. It pumps the hydrogens to
the outer compartment. And then that gradient, those
hydrogens that want to get back into the matrix,
essentially going back through this ATP synthase. This process of generating ATP
this way is called oxidative phosphorylation. It's a good word to know. You might see it on some
standardized tests or on your exams. And it's called
this because you have an oxidative part. Each of these molecules gets
oxidized in the electron transport chain as they lose
their hydrogens or as they lose their electrons. That creates a hydrogen
gradient. And then that, through
chemiosmosis, allows for phosphorylation. So that's another good
word to know. The transfer of these hydrogens,
these kind of going through this membrane
selectively. This membrane, this ATP
synthase, wouldn't allow just any molecule to go through it. It's allowing these hydrogen
protons to go through it. This process right here of this
hydrogen going through is called chemiosmosis. Another good word to know. So the entire process
is called oxidative phosphorylation. They don't happen at
the same time. Oxidative generates the energy
because the energy to push the hydrogens out. And then the phosphorylation
happens as the hydrogens experience chemiosmosis and go
back in and turn this little axle and then push the ADP and
the phosphate groups together. And then you can contrast
that with substrate. Substrate phosphorylations. Since I'm in the mood to
introduce you to terminology. Substrate phosphorylation. This is actually what happens
when the ATP is produced directly in glycolysis
in the Krebs cycle. And this is where you have an
enzyme directly helping to peruse the ATP without
any type of chemiosmosis or proton gradient. So if you imagine an
enzyme, some blurb, some big protein blurb. And let's say it has the
ADP there with its two phosphate groups. And then maybe it has another
phosphate group that attaches at some other part of the
enzyme, this enzyme facilitates without any kind of
chemiosmosis or oxidation. It facilitates, probably in
conjunction with other energy releasing reactions that may be
occurring on other parts of the enzyme. So maybe you can imagine a
little spark right there and then that twists this
entire enzyme. This isn't exactly how
it might work, but it's a good idea. And then these two things maybe
get pushed together. When it's just an enzyme
without any of this chemiosmosis that's driven by
oxidation, like we learned in the electron transport chain,
we call this substrate phosphorylation. And the substrates are just the
things that attach to the enzyme and have something
performed on them. So anyway, hopefully you
found this little video mildly useful.