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Glycolysis

by Georgina Cornwall, PhD
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    00:00 So moving into the whole process, we will start thinking about what glycolysis means.

    00:07 Glycolysis means specifically glyco-lysis, to split glucose into two.

    00:14 So that's exactly what we do. Glucose is a 6 carbon molecule and we're going to split it into two 3 carbon molecules.

    00:22 We are not going to get too involved in the details. Basically I'm going to give you an overview and some accounting to keep track of how much ATP is produced in each stage, as well as how many electron carriers are fueled in each stage.

    00:39 And then we'll keep track of carbons. Where do all these carbons go.

    00:44 You may recall that previously we have spoken about the idea of high energy containing bonds that are in glucose, so we have carbons strung to carbons. And in the process of cellular respiration, we're going to break these bonds, so we're going to split carbons off, steal the electrons, and take those electrons to the electron transport chain and chemioosmosis will reproduce the major amount of ATP that we use to run daily processes.

    01:15 So first of all, glycolysis is splitting of sugar, and then preparing those two pyruvate molecules to enter the Krebs cycle.

    01:25 Glycolysis is converting again our 6 carbon sugar into two 3 carbon pyruvates.

    01:32 So we are tracking carbons there. We still got six carbons at the end of glycolysis.

    01:37 Here is the overall process, a little bit more detail than we need to know.

    01:41 When you look into your biochemistry course, you'll start learning the name of every enzyme involved in each step of the pathway.

    01:49 And you'll also probably learn all the intermediates and you might even learn specifically how those electrons move around and the enzymes.

    01:56 But for the purposes of this course, you'll be introduced to again sort of the accounting and the general process.

    02:04 So there's two phases that we'll split glycolysis into. The first one is an energy investment phase.

    02:10 You'd recall that I made the analogy of burning a piece of wood because glucose is the same thing as wood essentially, its just the beta form of bonds that we're unable to break, but if we light them on fire, it undergoes a similar process but much more rapid and so we combust the wood all at once.

    02:30 But in order to get that wood started, we need to light a match, we need to give it a lighter, we need to maybe prepare a little bit and give it some energy. So just the same thing happens, when we metabolise glucose, we have an energy investment phase.

    02:46 So two ATP go in for each pyruvate that we oxidized. Two ATP come in, they come out as ADP, and they are ready to be phosphorylated again later in the process.

    02:58 But we split glucose in this energy investment phase. So it sort of takes energy to part those glucoses apart, you can think of it that way.

    03:07 During the energy harvesting phase, we will actually get some ATP yield as well as load up some of those taxis that I introduced you to in the last lecture.

    03:17 You'll recall the taxis are an analogy for the electron carriers, so in this case, we'll have NADs that are going to pick up electrons and hydrogens.

    03:27 Recall the electrons and hydrogens wore like couples, very excited to go to the school dance. They're on their way to prom.

    03:34 They need to get in a taxi or they need to get in a limousine, whichever vehicle they choose in order to get to the prom.

    03:40 And we're gonna carry these kids all the way to the prom, which is the very last phase of cellular respiration.

    03:47 So we'll continue the analogy all the way through.

    03:49 So now we've got our 6 carbon sugar split into two 3 carbon pyruvates, we'll see that the yield is two ATP for each pyruvate, so four total ATP as well as NADH. So we've added some electrons to the cars.

    04:11 So two NADs become two NADHs because they are carrying two electrons and hydrogens always carry with the electrons, so two hydrogens in addition.

    04:24 And then we'll have four ATP produced and that is by substrate level phosphorylation.

    04:32 There is the enzyme that comes along and picks up the ADP, adds a phosphate, so substrate level meaning it actually physically joins in an enzyme.

    04:42 So the substrate again being ADP, adding one phosphate, to make it ATP.

    04:49 So we have two ATPs invested and we've yielded four, so truly we've only made two ATP.

    05:00 And that's all we're going to get in glycolysis. Two ATP from the whole process.

    05:06 And many organisms only undergo glycolysis. They don't actually have any further processes.

    05:13 So glycolysis relatively yields a very small amount of ATP. But we do still have two 3 carbon pyruvates at the end of it, which means we have more carbons to split apart further on down the line and yield a ton more ATP.

    05:31 So let's move into looking at the summary of glycolysis. In glycolysis, this figure is all you need to know in one blue figure.

    05:41 So we have glucose, energy investment, energy release, we end up with two 3 carbon pyruvates, we've got two NADHs, and we've got two ATP net.


    About the Lecture

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


    Included Quiz Questions

    1. …cytosol of the cell only.
    2. …nucleus of the cell.
    3. ...cytosol and mitochondria of the cell.
    4. …ribosomes of the cell.
    5. …golgi bodies of the cell.
    1. Net ATP production per glucose molecule breakdown via glycolysis is 2 ATP.
    2. Glycolysis is an oxygen-independent metabolic pathway.
    3. Glycolysis pathway has two phases: Investment phase and Harvest phase.
    4. NAD+ acts as an electron acceptor during the glycolysis of glucose.
    5. Net ATP production per glucose molecule breakdown via glycolysis is 4 ATP.
    1. 2 x CO2
    2. 2 x Pyruvate
    3. All the Carbons from the original glucose
    4. Net gain of 2 ATP
    5. 2 x NADH = 4 electrons being carried

    Author of lecture Glycolysis

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD


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