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Oxidative phosphorylation and chemiosmosis

Oxidative Phosphorylation and Chemiosmosis (along with slight correction of previous video). Created by Sal Khan.

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  • blobby green style avatar for user wingwong51
    Can you (using a simple explanation) differentiate between oxidative phosphorylation, the electron transport chain, and chemiosmosis? Thank you so much!
    (54 votes)
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    • blobby green style avatar for user ccjenkins14
      Oxidative Phosphorylation is the big picture. The ETC and Chemiosmosis compose it.
      ETC - chain of enzymes that oxidize e- carriers to create energy that drives protons out of the membrane against it's concentration gradient
      Chemiosmosis - the production of ATP through the proton gradient "driving" the ATP synthase enzyme.
      (143 votes)
  • leaf green style avatar for user Rudy Unni
    Arenèt 36 ATP molecules produced from one molecule of glucose, not 38? because only 2 are produced from glycolysis (net)
    (6 votes)
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    • blobby green style avatar for user dondew228
      I teach Cell Respiration as:

      1. Glycolys (occurs in cytoplasm)
      (Glucose + 2 ADP + 2 Pi + 2 NAD --> 2 Pyruvate + 2 ATP + 2 NADH + heat)

      2. Pyruvate Processing
      (2 Pyruvate + 2 NAD + 2CoA --> 2 Acetyl CoA + 2 CO2 + 2 NADH + heat)
      Note.. The 2 carbons from pyruvate make up the acetyl part of acetylCoA. CoA is a big molecule that acts just as a carrier.)

      3. Krebs Cycle
      (2 AcetylCoA + 6 NAD + 2 FAD + 2 ADP + 2Pi -->
      4 CO2 + 6 NADH + 2 FADH2 + 2 ATP + 2 CoA + heat)

      4. ETC
      ( 10 NADH + 2 FADH2 + 34 ADP + 34 Pi + 6 O2-->
      34 ATP + 10 NAD + 2 FAD + heat)
      (Using conversion factor: 3 ATP/NADH and 2 ATP /FADH2)

      Total ATP production is 38 ATP per glucose.

      Note 1:
      Some books state 36 ATP per glucose but this occurs in cells that convert the 2 NADHs made in glycolysis into 2 FADH2s when they enter the mitochondria where Krebs cycle and ETC occur. If you do the math, you end up with 2 less ATP.

      This approach has worked well for over 30 years.

      Note2: The NADs and FADs produced in ETC… go back to glycolysis, pyruvate processing or the Krebs Cycle for use as inputs.

      Why do I talk about pyruvate processing?

      Because in Fermentation pyruvate is processed to either 2) lactate or 3) ethanol rather than 1) acetylCoA. So there are three types of Pyruvate Processing.

      Also pyruvate can be produced from other pathways such as fatty acid beta oxidation which can then be converted to acetylCoA and fed into the Krebs cycle.

      Note 4: Pyruvate vs Pyruvic acid?

      Pyruvic acid has an one more hydrogen than pyruvate
      Acids are H donors so

      Pyruvic acid ---> H+ + pyruvate

      So pyruvic acid and pyruvate are not really the same thing.

      Note 5: Criste are the ridges in the inner mitochondrial membrane, not THE inner mitochondrial membrane. Cristae increase the total surface area of the inner mitochondrial membrane which allows for more ETC systems per mitochondrion. Inside the inner membrane are protein complexes used by the ETC to pump NADH/FADH2 protons into the intermembrane space between the inner and outer mitochondrial membranes. Also in the inner membrane are the systems (ATP Synthase) used to put P on ADP to make ATP inside the inner membrane due to the passage of protons that were pumped out by the ETC.

      The ETC basically creates a battery where there are more protons on the outside than inside of inner membrane. So protons diffuse back to matrix due to proton concentration gradient and relatively negative matrix. So this is an electrochemical gradient driving ATP synthesis.

      (54 votes)
  • aqualine seedling style avatar for user REB84092
    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)
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    • aqualine ultimate style avatar for user River
      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)
  • blobby green style avatar for user anale.note
    What happens to the H+ atoms after they travel through the ATP Synthase?
    (5 votes)
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  • leaf blue style avatar for user Larry
    Please enlighten me on NADH and FADH. I searched the 8 lectures for an explanation to no avail.
    (8 votes)
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  • blobby green style avatar for user Scott Van de Motter
    Why do the H ions have to travel out of the matrix? Is there a gradient already present that they are following? As the H+ moves back into the matrix through the synthase, does the outer chamber then become basic?
    (4 votes)
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    • leaf green style avatar for user Brent Monk
      They would not travel out on their own. Energy is necessary to transport them out because there are more in the intermembrane space, causing both an electrical gradient (more + charge outside the mito. matrix) and a chemical gradient (more H+ present outside). If left to their own devices, H+ would want to move in, but the inner membrane is impermeable to most molecules, including H+.

      As the H+ comes back in through the ATP synthase, the intermembrane space would become slightly more basic than it was, but there is a huge quantity of H+ in the intermembrane space and only a little is moving in at a time through ATP synthase. In addition, while H+ is coming back in through ATP synthase, it is being pumped back out through the ETC chain. An equilibrium is established, and there is likely little if any net change in charge.

      Someone please correct me if I'm wrong.
      (5 votes)
  • leaf blue style avatar for user Kudrat
    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)
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    • leaf green style avatar for user Nahn
      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)
  • blobby green style avatar for user Rameen Muzaffar
    I can't understand what are electron carriers . Can you please tell me ?
    (3 votes)
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    • hopper cool style avatar for user Madeliv
      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)
  • blobby green style avatar for user jakegiles6312
    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)
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  • blobby green style avatar for user Saud Van Der Otaibi
    Thanx a lot for your help,

    but I still miss the FADH2's Role in the preocess. would you be so kind to clarify this concept.

    thanx again
    (3 votes)
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    • leaf green style avatar for user Kyle.Sullivan
      Saud - If you watch the previous video in this series (titled "Electron Transport Chain"), Sal mainly focuses on NADH's role in providing the bulk of the energy to produce ATP. However, there is a part where he briefly mentions that FADH_2_ contributes it's hydrogen ions as well, but they do not produce as much energy to contribute to making ATP because FADH_2_'s electrons are at a slightly lower energy level than NADH's electrons.
      (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.