Cell Respiration

by Georgina Cornwall, PhD

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    00:00 The point here is that electron transport chain and chemiosmosis are the primary ATP production area and they are utilizing all of the energy, the potential energy that was captured by the electron carriers bringing them to the electron transport chain. So let's talk a little bit about yields and where things come from. This figure is a fantastic summary of where each of those molecules come from. Our carbons, our electron carriers and our ATP. You'll notice that there are couple of ATP made directly through glycolysis. And there are couple of ATP that are directly made from the Krebs cycle.

    00:41 However, the majority of those ATP are going to be made from electron carriers that are carrying electrons to the electron transport chain.

    00:53 So we have a little bit of a currency we consider when calculating how many ATP get made from each glucose.

    01:01 And I have to tell you ahead of time, it's a little bit more complicated than it previously was thought.

    01:08 We previously made sort of an exchange rate for ATP and NADH and FADH. First of all, that we get 2.5 ATP on average per NADH per 2 protons, 2 electrons. And we get 1.5 for the FADH2. You'll recall that came in at a slightly lower level on the electron transport chain. And that means that in all we should have a certain number of ATP. Recall we got 2 from glycolysis, and we got a couple from the Krebs cycle.

    01:47 And when we consider all that we got from each of the processes, we should end up with 28, 30 ATP.

    01:57 You may have heard that there were 32 to 36 ATP made. This is where it gets confusing.

    02:04 When you do the accounting for what happens now that we are learning more about the ATP synthase molecule, some other ATP's may be lost. So let's just go with the number of around 30, and recall that this is probably the exchange rate that you'll be offered. And you can make your calculations based on that, but also be aware that probably there is a lot more going on and it's not quite as simple as we think.

    02:32 The accounting when it comes to ATP synthase doesn't quite work out. But we are still in the discovery stages of how that enzyme works. So let's look though at efficiency, because you'll be surprised that efficiency of glucose metabolism in the presence of oxygen is pretty good.

    02:54 Recall that glycolysis we make just a very little bit of ATP. And then the majority of it is made when we have oxygen present and can go through the Krebs cycle and can go into the electron transport chain and chemiosmosis. When we do that, we are producing 686 kcal/mol of glucose.

    03:17 And if you think about what ATP is worth. ATP is worth 7.3 kcal/mol. So when we do our math for this, we can divide the two and find out that considering 30 ATP was made on the most conservative side then we have a 32% efficiency which is more efficient than most cars on the road.

    03:43 Of course cars are getting much more efficient these days but still it's a pretty efficient system.

    03:48 When you consider that yeasts and such and some bacteria are anaerobic, they don't have the Krebs cycle or electron transport chain and chemiosmosis. They are only producing 2 ATP per glucose or, yeah 2 per glucose.

    04:05 And so it's not entirely an efficient system for them. So you think about how much more powerful it is to be able to use oxygen in the metabolism of our fuels.

    04:18 So, here is a summary figure of all of the stages we've been through.

    04:23 We had glycolysis which occurred outside of the mitochondria in the cytosol of the cell.

    04:29 We had to further oxidise the 2 pyruvates to get them across the mitochondrial membranes and into the matrix in the process of pyruvate oxidation. And then in the Krebs cycle, that occurs all the way on the inside of the cell. I mean in the site of the mitochondria. So then that we can pump the hydrogen ions out through the inner mitochondrial membrane into that intermembrane space, in order for chemiosmosis and oxidative phosphorylation to happen which is where we get all of our ATP. Again, this is a great summary image for the entire process of cellular respiration.

    05:08 By now, you should be able to track your carbons. You should be able to track your electron carriers as well as ATP. And where each of those is generated and where they go.

    05:20 For example, where do all these electron transporters go? You should be able to describe how the electrochemical gradient is formed during the electron transport chain.

    05:32 As well as the functioning of ATP synthase. How does that work in order to form so much ATP.

    05:41 So I hope you have a great understanding of cellular respiration at this point.

    05:45 I look forward to moving on to look at how different foods are metabolized, and how they fit into this process of cellular respiration. Thanks so much for listening.

    About the Lecture

    The lecture Cell Respiration by Georgina Cornwall, PhD is from the course Energy, Enzymes and Metabolism.

    Included Quiz Questions

    1. Mitochondria
    2. Golgi bodies
    3. Nucleus
    4. Lysosome
    5. Endoplasmic reticulum
    1. 32%
    2. 23%
    3. 20%
    4. 30%
    5. 38%

    Author of lecture Cell Respiration

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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