Lecture 13: Cellular Respiration 2 & Fermentation

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Hi, everyone.

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Welcome to your online lecture for today where we're going to be finishing up our discussion of cellular respiration, which is going to have a major focus on the energetic payout that produces the bulk of ATP.

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This is referred to as oxidative phosphorylation.

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And then we're also going to talk about our special guest today, which is fermentation, which is a process that some organisms are required to do to produce ATP, generally under very specific environmental conditions.

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But it's important because it's still supplements an ATP budget for an Organism, particularly when oxygen is actually missing.

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And so in that particular generation of energy, that's not an oxidative process where we're stealing electrons from somebody and driving them to do work.

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Or at least you don't get an abundance of electrons.

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It's sort of it's sort of net neutral and you end up producing little bursts of ATP repeatedly.

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I am sad because I love this Paramecium parlor, the cartoon from the Amoeba Sisters.

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But I'm concerned that your generation might not actually get the joke unless you have seen the the movie from the 90s, late 90s, early 2000s called Office Space, which is a cult classic, absolutely hilarious movie.

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But this is a nod to that where the boss is basically telling the employee, yeah, I'm going to need you to just keep coming to work forever and ever.

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In the movie, the boss tells the employee he's going to need him to come in and work on Saturdays.

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And the employee basically decides that he hates his job and he's going to sort of change his approach to the job.

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But I won't ruin the movie in case you'd like something absolutely ridiculous and so humorous to watch one of these weekends when you have some availability.

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But this yeast boss is asking its employee to just keep hitting the button to do glycolysis over and over and over again.

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And notice that the glycolysis machine almost resembles a Xerox machine, which is the source of grief and angst in the movie Office Space if you've ever seen it.

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I hope you do get a chance to watch that.

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Anyway, I think this particular cartoon is quite hilarious.

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So we left off in our last lecture talking about the first few steps in processing organic molecules by breaking them down or metabolizing them down to steal electrons from their bonds and release the carbon that was holding those electrons in place.

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So we talked about the first couple of steps.

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Glycolysis itself is the very first step, which is sugar breaking.

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So taking a glucose molecule and breaking it into two parts.

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So we were able to isolate a couple of pairs of electrons from a glucose molecule by simply ripping it in half, so 6 carbon into two, three carbons.

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And we were also able to produce just a tiny smidge of ATP doing glycolysis because of the nature of that chemical process.

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And that generates 23 carbon molecules referred to as pyruvate in any Physiology biochemistry class you ever take.

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Later you will probably hear about pyruvate again.

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It's just a three carbon skeleton that's an intermediate and many metabolic pathways that can be used to build other types of molecules or can go in reverse and be used to build sugar molecules.

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As much as we don't really do that because we're not green, we're not doing photosynthesis, we're not doing light driven production of sugar molecules.

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We can do a tiny bit of gluconeogenesis, which is basically taking half sugars and putting them back together again and storing them usually in our liver in the form of glycogen.

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We don't do a ton of that, but we can do a little bit of converting it backwards.

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But we talked about breaking sugar molecules, glucose molecules down into two pyruvates.

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And so those 3 carbon pyruvates are then transported into the matrix of the mitochondrion.

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So they have to cross the outer membrane, the Internet membrane space, and the inner membrane.

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Well, they don't go through the inner membrane, they go into the inner membrane space, as you can see here.

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Almost overstepped there.

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But this pyruvate gets further oxidized.

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So let's get one more bond chopped off of it and those electrons stolen and it releases carbon dioxide as part of waste.

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And so that molecule now that's been oxidized is going to be A2 carbon molecule called acetyl COA.

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And so we learned that acetyl COA is going to go into the Krebs cycle and that those bonds are going to be further broken down.

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Electrons are going to be further stripped out of the molecules that have gone into the Krebs cycle.

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And then we get a little bit of ATP produced from the Krebs cycle.

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But really the payout from all of this is the electrons that have been stolen and handed off to an electron carrier that's eventually going to transport those to the electron transport chain.

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Now the electron transport chain is what we're largely going to focus on today.

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Oh, and just as an aside, when you see Krebs cycle or TCA cycle, it's the same thing as a citric acid cycle.

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It has to do with sort of the early naming conventions and we've sort of migrated in a direction where we refer to it as the citric acid cycle, as citric acid is A4 carbon intermediate in that cycle.

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So we're going to see that the electrons that are harvested out of this original glucose molecule are going to be delivered to the electron transport chain.

5 minutes 31 seconds

This is a series of proteins that are embedded in the inter in the inner membrane all the way inside of the mitochondrion where you see all those folds or cristae.

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So it's going to the, the electrons are going to be transported to this series of proteins that do a job.

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And we're going to see what that job is and how it enables our cells to produce multiple more molecules of ATP at this last step than in all the previous steps of cellular respiration.

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So we refer to this as oxidative phosphorylation for a reason.

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So the name says it all.

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Something is going to get phosphorylated at the very end.

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And the oxidative part means that we've stolen a bunch of electrons from some other things.

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And we know it's the bonds from the sugar molecule to drive the work of doing the phosphorylation event.

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And the phosphorylation event is adding a phosphate onto ADP to make ATP.

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So we're using electrons we stole from somebody else to drive this process of phosphorylation.

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And it happens at this structure called the electron transport chain, and it drives a process called chemiosmosis.

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And we're going to see what that means, how chemiosmosis actually helps drive the phosphorylation of ADP into ATP.

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And our friend Homer is back as part of our running theme of deriving energy from organic molecules.

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And so the real payout is going to come from this particular step, these protein chains or groups that work together that are embedded in the inner membrane of our mitochondrium.

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And so the oxidative phosphorylation part, as I mentioned, is how we've removed electrons from glucose, from pyruvate, from acetyl COA, and we've isolated those electrons for use.

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Remember that electrons are energized when you pass them on to different proteins.

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It gets those proteins excited and they'll do their job, whatever their job is.

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And then as the electrons get past, past past, they start to get a little bit tired.

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I gave you early on an analogy like rolling down a hill.

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I gave you a little GIF of Ralph Wiggum standing next to Lisa Simpson rolling down a hill.

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And that analogy means that as you use an electron for its energy, kind of like you, if you you're doing work for something, you start to get tired.

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And then there generally needs to be something at the end of the process to catch the tired electrons because even tired or low energy electrons are reactive.

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They will interact with things and can make mistakes and errors.

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So we don't waste electrons and we don't let them wander off in our cells.

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They can be put into another molecule.

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They can be re energized to do the processes again.

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But we're going to see that really all we're going to use electrons for now is to power this electron transport chain.

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And it has a job that it's going to do in the inner membrane.

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OK.

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And so Orient yourself first.

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The outer membrane would be up here where the words are, where the text here is listed.

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The space between them, the outer and inner membranes of the mitochondrion is referred to as the inter or between membrane space.

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Remember, mitochondrion evolved from bacteria.

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And so it's got a second membrane on the outside that the cell that ingested it put on to protect itself from that bacterium and to sequester it and use it for its ability to produce ATP, OK.

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And so this particular mode of ATP production is, is different than the first one you learned.

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You learned a little bit about substrate level phosphorylation or you just have an enzyme that picks up ADP and inorganic phosphate and splashes them together.

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That's sort of one step process that can make a little bit of ATP.

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This generates quite a lot of ATP.

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And so this electron transport chain is going to receive the electrons that are carried by our carriers NADH and FADH 2.

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Remember, those are coming out of glycolysis, pyruvate oxidation, and the citric acid cycle.

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So we've got a bunch of electrons that are stored in these carriers.

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Remember, every NADH and FADH 2 is going to have two electrons that it's carrying.

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And also remember that they're more stable in their original versions.

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So NAD Plus is much more stable than NADH.

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And so NADH is very willing to sort of give up its electrons to this electron transport chain, which is more electronegatively stingy than the carriers are.

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They're willing to give them up, and then they go back to the citric acid cycle to receive more electrons.

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So what's going to happen here is the electrons are going to be passed to this group.

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Here we've got a few proteins embedded in the membrane complex 123 and four, and their principal jobs are passing the electrons around to each other.

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The most electronegative one is the one at the end, and so it generally helps vacuum the electrons through the whole chain and their function is to pump protons into the intermembrane space.

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So these are actually complexes that are made of lots of different proteins together that can accept electrons because they tend to have things like iron or and sulfur groups embedded in them, which can accept electrons, but they excite the complexes to move protons from the matrix space into the intermembrane space.

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Now remember what you've learned about diffusion and osmosis and facilitated diffusion.

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When you're moving things against their gradient, building something up in a space that really doesn't want to be there, that'll repels each other, it's you're going to require energy.

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So these electrons are providing that energy to move a bunch of protons into this tiny little space that's between the membranes, right?

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So this is going to end up producing an electrochemical gradient, which means that there's going to be a lot more hydrogen ions, right?

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So not only in number, but also in positive charge in that little intermembrane space and a lot less inside the matrix.

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So you could guess that those protons really want to escape that space and come back into the mitochondrial matrix and the cell.

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The mitochondrion is going to go, OK, cool, you can do that, but you can only come through one path.

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And that's going to drive the production of ATP through a process called chemiosmosis that we're going to talk about.

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All right, so we've got this chain here, and this is a little bit better view of what these electron transport chains are doing, but they're multi protein complexes and they have cofactors in them, which means that they will bind to things like iron atoms in order to function.

Otherwise they would not work.

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They've also got some members that pass back and forth handing electrons from complex to complex.

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So the very first complex that you see here is complex one.

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You can see it's embedded in the criste.

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Inside is the matrix, outside is the space.

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The space is where we're going to see the build up of the gradient of protons.

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And as an electron gets removed from NADH, which means it's going to be oxidized, that electron is going to pass to complex one and it's going to energize complex 1 to pump the proteins out to the space.

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Then it's gonna be passed on to a carrier called quinone.

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Now we saw something very similar to that in photosynthesis called plastoquinone.

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When we see something like phyto or plasto in the beginning of of a word tends to refer to it's happening in plants or specifically in plastids like the like the chloroplast.

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So quinone is a relative of that.

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And remember, chloroplasta and mitochondria are both evolved from bacteria, so they have somewhat similar carriers.

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And quinone has the ability to actually travel through the membrane even though it's holding on to electrons.

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And so it's going to receive electrons only from complex one.

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But complex 2 is also important.

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Even though it doesn't pump protons, what it does is it accepts electrons from FADH 2 and that's why FADH 2 is coming to this electron transport chain.

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It can only give its electrons to complex 2.

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So complex 2 is going to hand them off to quinone.

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So is complex one, and quinone is going to take them over to complex three.

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OK.

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Complex 3 is going to get excited by those electrons also and pump a bunch of protons out to that intermembrane space.

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And then those electrons are going to be handed off to another carrier that is peripheral to the membrane not going through it, called cytochrome C.

13 minutes 55 seconds

Cytochrome C is also going to give up or it's going to be oxidized and reduce complex 4.

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Complex 4 is also going to pump protons out to that intermembrane space.

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Waiting near complex 4 is the molecule oxygen, the job of which is to catch those tired, spent electrons.

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Remember, the most electronegatively stingy things we could have in our cells are usually oxygen or nitrogen.

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We don't have a bunch of nitrogen in our cells.

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That's waiting for electrons.

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We have a ton of oxygen because we live in an oxygen rich environment and we use a lot of oxygen in our processes.

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OK.

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And plus, we're water based and oxygen is generally part of water, which is pretty harmless.

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Now the trick here is you don't just want to hand off electrons to oxygen because what you end up producing there is reactive oxygen or Ross, and we probably heard that reactive oxygen species are very damaging and they they are, they can create oxide ions, they can pick up one or more electrons and then oxygen will start to interact with different things like proteins and nucleic acids and damage them.

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So the safest thing to do once you hand some electrons to oxygen is also give it some protons, which we have plenty of floating around here.

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And we know that if we give oxygen electrons and protons, we just make water.

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So water is a a harmless product, a harmless waste product that comes out of this process.

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And so oxygen being at the end of this is actually helping to vacuum electrons all the way through this chain because it's the most electronegatively stingy.

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Complex one is the least stingy.

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Complex 2 is a little more stingy.

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Complex 3 is a little more stingy with electrons.

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Complex 4 is even more stingy.

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Oxygen is the most stingy.

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And so it's going to pull these electrons through the chain to do this work, all right.

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And so it's going to build up this electrochemical gradient of protons in that space.

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Now, those protons are really dying to get away from each other.

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They are all positively charged and they're in high concentration, so they absolutely repel each other.

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But what this membrane has set up is only one path for them to leave that intermembrane space and by allowing them to leave that space it can harness those protons to do work.

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OK.

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This is called a proton motive force or proton driven force.

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And building up a gradient of protons and then asking them to move by diffusion through a transporter and get them to do work is referred to as chemi osmosis.

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OK.

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And this is actual active diffusion of the protons, but they're driving the process of work, OK.

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And so they're going down their gradient, but they're forcing some actual work to occur.

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Now chemiosmosis resembles something like this.

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So let's say you've got a very high ion concentration on one side or regular chemical concentration, and those molecules really want to move down their concentration gradient to where the concentration is much lower on the other side.

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But charged atoms or charged charged particles like a proton can't just move through the membrane.

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They don't do that.

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So they have to have a pathway to get through.

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And so we've evolved that pathway and harnessed it to something that actually does work for us.

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And so getting the protons to go through one channel that actually turns causes that Channel to do some work.

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It's kind of similar to looking at something like a hydroelectric dam.

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OK, so when you store water, this is the Hoover Dam.

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I don't know if you've ever been there, but you can kind of tell that the water here is pushed up behind a wall.

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Now think about where does that water want to go?

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If you were to just remove that wall, what would happen?

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Whoosh, right?

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The water would all of a sudden have kinetic potential instead of kinetic energy.

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Instead of potential energy right here.

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It's got a bunch of potential energy because it's up high and it really wants to come down with the flow of gravity.

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But if you put it behind the wall and then you allow it only to exit through a certain area, you can get it to turn rotors or pumps and produce electricity or produce some form of energy because of the movement.

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And so this is the same kind of feature that happens in our in our mitochondria.

18 minutes 31 seconds

We have a protein complex called ATP synthase that serves as this pathway through the membrane that protons will flow through.

18 minutes 42 seconds

Now imagine what would happen if you also poked a hole in the wall of the dam.

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If you poked a big hole in the wall, water would leak out of it also.

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But that water isn't harnessed to any kind of motor or machine that would drive work.

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You would just sort of lose the gradient if you poked a hole in the wall.

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OK.

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And so that's why this membrane is intact.

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Only way out is through ATP synthase.

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And so ATP synthase is a very large enzyme complex that sort of looks like a doorknob if you turn it up right.

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Sometimes it looks like a Tulip in some figures.

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It's made of multiple different parts, and sometimes it's useful, as you know, for engineering purposes to recognize what the parts are.

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Also, because we use this same complex in many eukaryotic organisms and we have two different versions that run in opposite directions to do different things for us, which is pretty impressive.

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Turns out, even in evolutionary biology, if it ain't broke, you don't fix it.

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You use the same technique and structure if it works really well.

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So this particular enzyme complex has an F0 subunit that kind of looks like where the doorknob would be inserted into the door.

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All right, And then it's got this sort of stationary structure.

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Then there's a little gap in between the two of those that provides a pour directly through the membrane.

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All right, So protons are going to end up going through that pour.

20 minutes

On the other side, inside the mitochondrial matrix, which is where we would want to release our ATP to right, to be able to be sequestered or used or transported out of the mitochondrion, we're going to see inside, there's going to be what's called a rotor, and there's a shaft of this.

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And then at the bottom that what looks like the doorknob part is the F1 unit and all the enzymatic activity happens in those little subunits.

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And then this long part right here is also really important.

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This is called the stay tour, which sounds like stay or stay in place.

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And so this is important to remember because we often look at this and assume that the doorknob rotates, but it does not.

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All of these subunits that are in light green stay in the same place.

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Only the rotor spins in the middle.

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OK, so for every three to four protons that flow through this, it causes a a turn of the F0 subunit, which causes the rotor to move.

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And this rotor shaft, as it turns clockwise, basically thumps on the back of all these little green subunits and causes them to pick up ADP and Pi and smush them together to produce ATP.

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So every single one of these little green subunits down here takes a turn with ADP, inorganic phosphate, puts them together, creates that covalent bond, and then releases ATP.

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OK.

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And so for, like I said, for every three to four protons that flow through, it causes a rotation and you end up producing ATP molecules.

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Now, we have this same exact structure in other places in our cells as do plants.

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That goes in reverse.

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It can hydrolyze ATP to force protons into an actual compartment.

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OK.

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And that's called an ATP ace.

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So you're going to learn about ATP synthase like this one that makes ATP, and in other cases you'll learn about ATP ACE that breaks down ATP to drive the flow of protons in another place.

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For now, you need to know that this is the maker ATP synthase.

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Notice the name looks like synthesis.

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OK.

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And so only this middle part is actually going to spin.

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The stator actually helps hold all the F1 subunits in the same place.

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And you've got ATP synthase in all cells all over your body.

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And so it acts like a molecular motor.

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And this flow of protons through the F0 is going to drive that movement, OK.

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And so every single subunit here is going to catalyze ADP plus Pi to ATP, which also means that your mitochondria needs to constantly export ATP and bring back in ADP.

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And PIPI is inorganic phosphate, 1 phosphate functional group that gets put on to ADP.

22 minutes 49 seconds

Remember, ADP, it already has two phosphates.

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If you add a third, you produce ATP.

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And so by doing this particular chemiosmotic process, you get an additional 25 ATP molecules on top of everything that came before in all the different steps of cellular respiration where you didn't really make that much, right?

23 minutes 8 seconds

We only netted a few, a few ATP in those steps.

23 minutes 12 seconds

And so the summary of glucose oxidation, the whole summary, the overview without all the finer details is that we've got glucose in the cytosol, that we breakdown 6 carbon sugar that we pull apart into two, three carbon sugars known as pyruvates.

23 minutes 26 seconds

We've already harvested 4 electrons, right?

23 minutes 29 seconds

If you think about that, if you think that there's bonds between all the carbons and you break 2 bonds from the circular thing, you get, right, two electrons and two electrons.

23 minutes 39 seconds

And so you get 4 electrons from breaking it in half.

23 minutes 42 seconds

And then remember, it required a little bit of input of ATP, but we ended up getting double back.

23 minutes 47 seconds

And so we net just a tiny bit of ATP.

23 minutes 50 seconds

Every time we do glycolysis, that pyruvate gets transported across both membranes into the matrix.

23 minutes 55 seconds

It's going to be oxidized further, which means we cut one more bond off of both of them.

24 minutes

And so that's two electrons and two more electrons that we hand to NADH, right?

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So that's four electrons and we release a couple molecules of carbon dioxide, those two acetyl Coas that are left fed into the citric acid cycle.

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And by chopping those down and releasing the remaining carbon atoms, we get 6 molecules of NADH.

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So that's 12 electrons there.

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Two more FADH 2, so that's four more electrons there.

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That's good.

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That's 16 electrons just from the citric acid cycle and we get a little bit additional ATP.

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Remember that at the end, once you're sort of, you get to the to the succinyl COA, it's sort of just a swapping thing where you use the phosphate as a placeholder and then you take it off again to leave oxygen behind.

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And that's how you recycle the rest of the cycle.

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And you just happen to get a little ATP off the top there.

24 minutes 45 seconds

And so you end up producing a few molecules of ATP.

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The very end though, is the real payout, glucose oxidation.

24 minutes 52 seconds

You get some electrons and release CO2, but the real big bonus happens in the payoff phase, which is your oxidation.

24 minutes 59 seconds

It's the date of phosphorylation where you're passing the electrons that you've harvested along and you're producing this chemi osmotic gradient that then goes through ATP synthase and makes all the extra ATP.

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All right, so if we got two ATP here and two ATP here, but we got a payout of about 25 here.

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And so I always say about because depending on the number of protons that run through ATP synthase, you might get a little bit more than that.

25 minutes 21 seconds

But this is the sort of conservative estimate that in total you're going to get about 29 molecules, 29 to 31 molecules of ATP for every glucose you breakdown.

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That's pretty good.

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That's quite a lot of energetic currency for breaking down single glucose molecules.

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So if you don't get to the end of this, all the way to the end in the electron transport chain, you don't get that much ATP.

25 minutes 44 seconds

You literally have to get all the way through this in order to get this much ATP.

25 minutes 49 seconds

And in order to get all the way through this, one of the biggest things you have to have is you got to have oxygen at the end.

25 minutes 54 seconds

There's got to be something that's catching all the spent electrons at the end of this.

25 minutes 59 seconds

Now, some organisms, many bacteria, for example, like the ones that live in extreme environments or the ones that live in your guts, for example, they do this in environments where there is not a lot of oxygen.

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And instead of having oxygen as a catcher at the end, they use nitrogen for that purpose.

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We don't do that.

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We live in a largely oxygenated environment.

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There's a lot of nitrogen too, but we just haven't evolved to use it.

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And so nitrates or nitrites into nitrates, I think it is, I can't remember which direction it is.

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But anyway, I think it's, I think it's nitrates that they use, that bacteria use.

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They can catch electrons with nitrogen instead of using oxygen and they can still end up doing this process.

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Now keep in mind also your mitochondria evolved from bacteria and that must mean that bacteria also have the ability to do cellular respiration instead of having an organelle like a mitochondrion.

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Bacteria use their plasma membrane.

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So they have folds in their plasma membrane that supports the electron transport chain and they do this interaction with the cytoplasm, with the external environment.

27 minutes 7 seconds

They bring in sugar molecules from outside the cell and they bring them into their cytoplasm, and they do the rest of this using their plasma membrane.

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And so bacteria can do this as well.

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They've been doing this for a long time, right?

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So this evolved in our cells from them.

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All right, so just as a real quick summary of the whole process, which is usually good for people, sort of tying together all the concepts that we've talked about in cellular respiration, here's a really good Bioflix video demonstrating the processes.

27 minutes 37 seconds

As this mountain biker heads up the trail, the breakfast he ate this morning is being burned to power his bike ride.

27 minutes 44 seconds

His breathing rate increases as his leg muscles demand more oxygen to burn more fuel.

27 minutes 49 seconds

Let's zoom down to where this fuel is burned, our cells.

27 minutes 53 seconds

Here, the blood vessel on the left delivers fuel and oxygen to a single muscle cell.

27 minutes 58 seconds

In cellular respiration, energy and fuel is converted to ATP, shown here as starbursts.

28 minutes 5 seconds

Most ATP is made in the cells mitochondria.

28 minutes 8 seconds

ATP powers the work of the cell, such as contraction.

28 minutes 15 seconds

Let's take a closer look at how ATP is produced from a molecule of glucose, our fuel.

28 minutes 21 seconds

Only the carbon skeleton is shown to keep things simple.

28 minutes 24 seconds

The first step is called glycolysis and it takes place outside the mitochondria.

28 minutes 29 seconds

To to begin the process, some energy has to be invested.

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Next, the molecule is split in half.

28 minutes 35 seconds

Now the molecule NAD plus an electron carrier picks up electrons and hydrogen atoms from the carbon molecule, becoming NADH.

28 minutes 45 seconds

Keep track of the electron carriers, they play an important role by transporting electrons to reactions in the mitochondria.

28 minutes 52 seconds

In the final steps of glycolysis, some ATP is produced, but not much.

28 minutes 57 seconds

For every glucose molecule, only two net AT PS are produced.

29 minutes 1 second

Outside the mitochondrion, however, glycolysis has produced pyruvic acid, which still has a lot of energy available in the bonds the electrons.

29 minutes 12 seconds

Let's follow this pyruvic acid molecule into a mitochondrion to see where most of the energy is extracted.

29 minutes 18 seconds

As the molecule enters the mitochondrion, 1 carbon is removed, forming carbon dioxide as a byproduct.

29 minutes 26 seconds

Electrons are stripped, forming NADH.

29 minutes 29 seconds

Coenzyme A attaches to the two carbon fragment, forming acetyl COA.

29 minutes 38 seconds

Coenzyme A is removed and the remaining 2 carbon skeleton is attached to an existing 4 carbon molecule that serves as the starting point for the citric acid cycle.

29 minutes 49 seconds

The new 6 carbon chain is partially broken down, releasing carbon dioxide.

29 minutes 54 seconds

Several electrons are captured by electron carriers and more carbon dioxide is released.

30 minutes

The carbon dioxide that you exhale comes from the reactions of cellular respiration.

30 minutes 6 seconds

2 AT PS are produced by the citric acid cycle for each molecule of glucose.

30 minutes 11 seconds

At this point, only a small number of AT PS have been produced.

30 minutes 17 seconds

However, more energy is available in the electrons that are being transported by electron carriers while the citric acid cycle starts another round.

30 minutes 26 seconds

Let's follow an electron carrier to the next step in the process.

30 minutes 33 seconds

Electron carriers such as NADH deliver their electrons to an electron transport chain embedded in the inner membrane of the mitochondrion.

30 minutes 42 seconds

The chain consists of a series of electron carriers, most of which are proteins that exist in large complexes.

30 minutes 51 seconds

Electrons are transferred from 1 electron carrier to the next in the electron transport chain.

30 minutes 57 seconds

Let's take a closer look at the path electrons take through the chain.

31 minutes 1 second

As electrons move along each step of the chain, they give up a bit of energy.

31 minutes 9 seconds

The oxygen you breathe pulls electrons from the transport chain, and water is formed as a byproduct.

31 minutes 15 seconds

The energy released by electrons is used to pump hydrogen ions, the blue balls, across the inner membrane of the mitochondrion, creating an area of high hydrogen ion concentration.

31 minutes 26 seconds

Hydrogen ions flow back across the membrane through a turbine, much like water through a dam.

31 minutes 32 seconds

The flow of hydrogen ions spins the turbine, which activates the production of ATP.

31 minutes 37 seconds

These spinning turbines in your cells produce most of the ATP that is generated from the food you eat.

31 minutes 44 seconds

The process you've just observed, cellular respiration, generates 10 million AT PS per second in just one cell.

31 minutes 52 seconds

That ATP can power a biker up the trail, or it can power your brain cells as you learn challenging biology topics.

32 minutes 1 second

I know cellular respiration in all of its components can be really challenging to learn, but when you see it applied like that and you think about how impressive it is, it's actually kind of fun to learn.

32 minutes 12 seconds

All right, So one thing we need to talk about that is quite complementary to this process, and it's also something that we take advantage of not only in ourselves but also for our own agricultural and economic purposes, is a process called fermentation.

32 minutes 27 seconds

And so fermentation is a very short term solution for energy production when oxygen is limiting for an Organism, OK.

32 minutes 37 seconds

So this is sort of like starting and going only a short way and then starting and going only a short way and doing that over and over and over again to make little bits of ATP to kind of keep you alive.

32 minutes 48 seconds

OK.

32 minutes 48 seconds

And so there's a reason that there is that Homer is holding a beer on this particular slide because beer is one of the types of libations that is generated from the process of fermentation.

32 minutes 59 seconds

Of course, we also make lots of things from the process of fermentation that are beneficial to us.

33 minutes 4 seconds

OK, so we've already learned about glycolysis and this is sort of the oldest universal energy harvesting process of living organisms.

33 minutes 13 seconds

It's one of the simplest that we've been able to evolve to have in order to breakdown organic molecules like sugars and also fats.

33 minutes 23 seconds

OK, So this part is the very first part you learned about in respiration, but it is also the most central part of fermentation.

33 minutes 31 seconds

The fact that we share this in common with prokaryotes means that it's probably the oldest process.

33 minutes 38 seconds

OK.

33 minutes 38 seconds

Some prokaryotes don't do the rest of the processes like the electron transport chain.

33 minutes 44 seconds

Some prokaryotes live in in environments where they don't have the ability to use this or we'll see that some single celled eukaryotes like yeast have the ability to keep doing glycolysis over and over and over again when oxygen is is limiting or unavailable.

34 minutes

And so this is a very old process.

34 minutes 2 seconds

We share a lot of the same genes and steps of the pathway in common with other smaller bacteria and eukaryotes.

34 minutes 9 seconds

So that suggests that this pathway is really old, right?

34 minutes 12 seconds

So we're talking 3.5 billion years old when prokaryotes were the only thing on the planet, OK.

34 minutes 18 seconds

And so when the the process still works, you don't tend to change it much even over that length of time.

34 minutes 24 seconds

And so all domains of life do glycolysis, which suggests that we have that in common with all organisms, which suggests that glycolysis itself is very, very old.

34 minutes 35 seconds

Not to mention where it's located in a cell doesn't involve membrane enclosed and membrane enclosed organelles with a, with a breakdown happens.

34 minutes 45 seconds

So it's very likely that it existed long before organelles like mitochondria, right?

34 minutes 51 seconds

So bacteria have been doing glycolysis for a really long time and eukaryotes evolved from prokaryotes.

34 minutes 56 seconds

So that's where we got it from.

34 minutes 58 seconds

So remember, this is the process of sugar breaking.

35 minutes 1 second

We know that there's an energy investment phase where in order to break something down, you have to put in a little bit of work.

35 minutes 6 seconds

In other words, you have to power an enzyme to help break it apart, but then you end up taking back some of the energy in the form of ATP.

35 minutes 15 seconds

In reality, and you just saw in the video that shows what we're going to do is we're going to steal electrons and satisfy what we've stolen with some phosphates.

35 minutes 24 seconds

And then we don't want to add more to glucose molecule really we're just using that temporarily to break it apart.

35 minutes 29 seconds

We're going to take, take those phosphates back again because we're trying to break this down into simple carbons, right, Simple carbon dioxide molecules.

35 minutes 36 seconds

We don't want to add phosphates.

35 minutes 37 seconds

This is a placeholder to help energize that and break it apart further.

35 minutes 41 seconds

So when we, you, you saw in the video that our first energy investment breaks apart the glucose molecule and you end up with three carbon molecules that have phosphates on the ends.

35 minutes 51 seconds

And then we have inorganic phosphate floating around already that we use to phosphorylate the other ends of this, OK?

35 minutes 59 seconds

And we are going to convert this 3 carbon molecule into pyruvic acid or pyruvate by taking those phosphates back again.

36 minutes 6 seconds

And when you take off inorganic phosphates from any molecule, the best thing to do is to throw them right back onto ADP and you end up making ATP.

36 minutes 13 seconds

So even with a small investment, you net in the energy harvesting phase or the payout, you net to additional ATP that you didn't already start with, as long as you've got a pool of inorganic phosphate floating around, OK.

36 minutes 25 seconds

And so fermentation will allow cells, even ours, to produce ATP if we don't have oxygen.

36 minutes 32 seconds

And you can imagine different types of scenarios where you might be running low on oxygen.

36 minutes 36 seconds

For us, it tends to be, you know, not things you see in movies like we're in a boat and there's no breathing air or you're stuck in a chamber and they're vacuuming out.

36 minutes 44 seconds

The, it's more like you're doing too much activity, right?

36 minutes 47 seconds

And you're, you're converting most of your oxygen into water while you're doing cellular respiration and you're running out.

36 minutes 52 seconds

This is why we breathe heavier to try to bring more oxygen in.

36 minutes 55 seconds

But you can end up running low on oxygen when you're when you're doing too much activity.

36 minutes 59 seconds

And so this is a life saving feature in your cells, but it's not a permanent way of survival because it only gives you a little bit of energy without needing any oxygen.

37 minutes 8 seconds

Remember, the oxygen is at the end of the electron transport chain.

37 minutes 11 seconds

So if you don't have oxygen, you can't do the electron transport chain.

37 minutes 14 seconds

All you can do is glycolysis over and over and over again.

37 minutes 18 seconds

OK.

37 minutes 19 seconds

And so in the process of fermentation, that's basically what it is.

37 minutes 23 seconds

It's starting glycolysis and then starting glycolysis and then starting glycolysis.

37 minutes 26 seconds

And you just keep doing glycolysis over and over and over again, and you end up with some different products depending on what cell type you are.

37 minutes 34 seconds

There is ultimately no net removal of electrons.

37 minutes 37 seconds

You're not gaining electrons to use them elsewhere.

37 minutes 40 seconds

You're getting electrons and then putting them right back in, getting some electrons and then putting them right back in.

37 minutes 45 seconds

It's completely circular.

37 minutes 46 seconds

You don't get any gained electrons out of fermentation.

37 minutes 49 seconds

It just keeps cycling and making a couple of AT PS over and over and over again.

37 minutes 53 seconds

And so glycolysis is used as the first step of fermentation and you end up getting two ATP molecules out of that step.

38 minutes

You end up doing the same thing you would in cellular respiration by producing 2 pyruvates.

38 minutes 5 seconds

But then those pyruvates have to be converted into something else.

38 minutes 8 seconds

And the reason is that you have to replenish the pool of NAD plus.

38 minutes 15 seconds

So remember in the first part of glycolysis, when we break apart glucose and we steal some electrons, we take two molecules of NAD plus and we hand the electrons to them.

38 minutes 24 seconds

So we have 4 electrons into NADH, and then NADH goes off to the electron transport chain.

38 minutes 30 seconds

Well, if you don't have oxygen, you don't get to use the electron transport chain.

38 minutes 33 seconds

And so you can't have a bunch of NADH floating around #1 NADH is actually kind of dangerous if you don't allow it to give its electrons to the right place, because NADH will go around looking for anybody to give its electrons to, and you don't want that happening.

38 minutes 51 seconds

You don't want NADH just throwing electrons on anything because then that thing becomes reactive and then you can cause damage.

38 minutes 58 seconds

The other reason that you have to get rid of those electrons is that you need to get NAD plus generated back again to go do glycolysis again.

39 minutes 7 seconds

In order to keep doing this, you have to keep stealing electrons and giving them to something and getting NAD plus back to the beginning of this path.

39 minutes 15 seconds

So you see here pyruvate, this 3 carbon gets converted into something called lactate are often called lactic acid.

39 minutes 23 seconds

And that happens by reduction.

39 minutes 25 seconds

When you reduce pyruvate with four electrons, you can convert those two into lactate and then NADH is free to go back to the beginning of the pathway again.

39 minutes 33 seconds

So that's why this has to these have to be recycled.

39 minutes 35 seconds

They're not going to the electron transport chain.

39 minutes 37 seconds

The electron transport chain won't work because you have no oxygen and so this is an anaerobic path for recycling NADH back to NAD plus.

39 minutes 47 seconds

So there's no oxygen involved.

39 minutes 49 seconds

That's what anaerobic or against aerobic.

39 minutes 52 seconds

Aerobic means with oxygen, anaerobic is without.

39 minutes 55 seconds

OK, so this happens in your muscle cells and also in certain types of bacteria by production of something called lactate or lactic acid and lactic acid.

40 minutes 7 seconds

Has got a bad rap.

40 minutes 8 seconds

This has been debunked since the 1980s yet people still believe that that is the thing that causes your muscles to burn.

40 minutes 14 seconds

That's not the case at all.

40 minutes 17 seconds

Lactate may build up and you can detect it in the bloodstream and usually what happens is it gets cleared by your liver.

40 minutes 23 seconds

Your liver will take the lactate out.

40 minutes 25 seconds

It's just a three carbon sugar that can then be converted back into glucose once you have re established the oxygen that you need.

40 minutes 33 seconds

OK, and so remember lactate, lactic acid's got a bad wrap.

40 minutes 36 seconds

That's not the thing that's causing your muscles to burn when you are working out and not getting enough oxygen, but it is an indication that you're not getting enough oxygen.

40 minutes 46 seconds

Maybe you need to slow down on your activity or control your breath better to get more oxygen.

40 minutes 51 seconds

And so lactate can be recycled back into glucose if absolutely necessary.

40 minutes 56 seconds

But this is just an output that helps you regenerate NAD plus by converting, by reducing pyruvate into lactate, so freeing up NAD plus by getting rid of the electrons that it was carrying, That's absolutely necessary.

41 minutes 9 seconds

And so like I said, usually your liver can clean it out.

41 minutes 12 seconds

You can convert it back to pyruvate and pyruvate can can go right back into the mitochondria.

41 minutes 19 seconds

If all of a sudden your oxygen recovers, you've got a now pool of pyruvate that you could use to continue driving the citric acid cycle.

41 minutes 28 seconds

And so another type of fermentation that often times microorganisms do, especially eukaryotes like us, like yeast can do a similar type of fermentation, producing lactic acid to make bacteria do this to make cheese and yogurt.

41 minutes 45 seconds

And so we think about fermented foods often use bacteria and they put they can they can make that sort of tangy taste of cheese and yogurt and will often they're super beneficial for us minimally they taste amazing.

42 minutes

But other types of microbes, this tends to be some bacteria and yeast can actually ferment things, sugar sources into other types of sort of tangy fermented things like soy sauce and by fermenting the cellulose in cabbage, or it's probably glucose in cabbage into sauerkraut.

42 minutes 20 seconds

So you probably had some things that taste pickled or fermented.

42 minutes 22 seconds

Those are actually quite healthy, particularly for our microbiome in our guts.

42 minutes 27 seconds

And then one of the most important and some of our favorites, or if you're not of legal age yet, it might be some of your favorite someday, is where we use things like yeast, which are single cell eukaryotic fungi, individual funguses, fungi that can do alcohol fermentation.

42 minutes 43 seconds

So this is a very similar process to what happens in fermentation to produce lactic acid, except there's an additional step where you lose carbon dioxide.

42 minutes 53 seconds

So there are enzymes after the glycolysis process where you've pruded the the two pyruvates that will then reduce pyruvate into two molecules of ethanol, but will release some of the carbons in the form of carbon dioxide.

43 minutes 9 seconds

And so if you've ever wondered about beer brewing, this is a big deal 'cause I came from Wisconsin, I'm not from there originally.

43 minutes 16 seconds

I'm from Chicago, but I went to Graduate School at the University of Wisconsin, Madison.

43 minutes 20 seconds

And beer brewing in Wisconsin is huge and also very scientific because bulk fermentation processes can be used to make cellulosic ethanol, which can be used to power machinery.

43 minutes 31 seconds

And so it's not just about drinking beer and wine.

43 minutes 34 seconds

It's also about understanding how to produce cellulosic ethanol that can be used to power machines like our cars.

43 minutes 40 seconds

And so this process is widely studied there also.

43 minutes 43 seconds

We love beer and wine, right?

43 minutes 45 seconds

And So what the the industry does is it uses a source like plant material.

43 minutes 50 seconds

So the best beers are made from things like barley.

43 minutes 55 seconds

Crappy beers are made from things like corn and rice, right?

43 minutes 57 seconds

If you drink Bud or Miller or Corona, you're probably getting corn or wheat or rice beer.

44 minutes 3 seconds

There's not a lot of rice beers.

44 minutes 4 seconds

It's mostly corn and wheat.

44 minutes 6 seconds

Those tend to be the crappiest beers, but that's the most regularly available, cheapest sugar.

44 minutes 11 seconds

And what beer Brewers will do is they will allow those plants to germinate very briefly, which means the plant, the seeds starts to wake up and loosen up its sugars.

44 minutes 24 seconds

And then they'll cook all of those germinated seeds to release the sugars into a water solution that you cook it really hot and it's called wart WORT.

44 minutes 35 seconds

They'll spin out all the plant matter and basically now they've got plant sugar water.

44 minutes 39 seconds

And then what they'll do is they'll take that plant sugar water and they'll put microbes in it like beer brewing yeast.

44 minutes 45 seconds

And they come in a couple of different varieties.

44 minutes 47 seconds

So there's specific types of yeast that are for making loggers versus ales, like one yeast will float on the bottom 11 or what settles on the bottom, one yeast floats on the top.

44 minutes 56 seconds

And then they use different types of yeast for fermenting grape juice to make wine.

45 minutes 1 second

And So what the yeast does is it takes in the glucose from the environment and that environment happens to be a low oxygen environment.

45 minutes 9 seconds

So this forces the yeast to actually do fermentation.

45 minutes 13 seconds

And in the process of fermentation, what the yeast produces as it metabolizes these sugars to make ATP for itself is produce molecules of ethanol, which we know is the alcohol that is in beer and wine, and by default produces CO2 as a byproduct as well.

45 minutes 34 seconds

And CO2 is what gives things like beer and sparkling wines the bubbles, right?

45 minutes 40 seconds

CO2 and any gas is hard to keep dissolved in a liquid, and so with enough time you can usually get rid of the CO2 gas.

45 minutes 48 seconds

There's, I'm sure wine makers have a clever way of getting the CO2 out of the wine that they don't want to be bubbly.

45 minutes 55 seconds

But if you've had champagne and if you've had beer or if you've had rose or sparkling wines, the bubbles are generally coming from the yeast.

46 minutes 3 seconds

Now, some types of alcohols, they add additional CO2 cartridges into them to give them more bubbles because they tend to get flat quickly.

46 minutes 12 seconds

But generally the CO2 is, is, is produced from the microorganism that's inside of the fluid as well.

46 minutes 19 seconds

And this has been going on for hundreds and hundreds of years.

46 minutes 22 seconds

Blame it on the, the monks that started brewing beer up in the the the monasteries to because it kept well, it kept well fermented things keep well.

46 minutes 33 seconds

All right.

46 minutes 33 seconds

So here's a real quick, real quick, not super thorough overview of the different types of fermentation right generating generated after the same pathway of glycolysis.

46 minutes 46 seconds

All cells are able to synthesize ATP via the process of glycolysis.

46 minutes 52 seconds

In many cells, if oxygen is not present, pyruvate is metabolized in a process called fermentation.

46 minutes 59 seconds

By oxidizing the NADH produced in glycolysis, fermentation regenerates NAD plus, which can take part in glycolysis once again to produce more ATP.

47 minutes 9 seconds

The net energy gain in fermentation is 2 ATP molecules per molecule of glucose.

47 minutes 15 seconds

Fermentation complements glycolysis and makes it possible for ATP to be continually produced in the absence of oxygen.

47 minutes 22 seconds

So it's pretty.

47 minutes 23 seconds

There are two types of fermentation.

47 minutes 25 seconds

The alcohol fermentation, which occurs in yeast, results in the production of ethanol and carbon dioxide.

47 minutes 31 seconds

Lactic acid fermentation, which occurs in muscle, results in the production of lactate.

47 minutes 37 seconds

I seem to recall that video being much shorter, but I'm happy she had more to say.

47 minutes 40 seconds

So notice that glycolysis is the step is the same for both, right?

47 minutes 44 seconds

You're breaking a sugar molecule in half and you produce the net ATP that you would if you were doing regular cellular respiration.

47 minutes 50 seconds

But the blockage becomes here at going into the mitochondria.

47 minutes 54 seconds

And when you don't have enough oxygen or you're forced to live in an environment like bacteria and yeast might be to do fermentation, there is no oxygen.

48 minutes 2 seconds

And So what this allows you to do is take those pyruvate molecules and feed them into one pathway or the other.

48 minutes 7 seconds

And in our cells, obviously, we're going to have lactate produced.

48 minutes 12 seconds

Notice it's still A3 carbon sugar.

48 minutes 13 seconds

And as I mentioned, it can be converted back into pyruvate if oxygen does show up.

48 minutes 17 seconds

And then you can throw it into the mitochondrion and then continue or resume what you would have done as far as citric acid cycle and electron transport chain.

48 minutes 26 seconds

And then in these microorganisms basically oxidizing NADH into NAD plus and handing those electrons off to pyruvate, you can convert it into ethanol and CO2 and release the bubbles and the alcohol.

48 minutes 43 seconds

And so those are processes for like starting over and starting over and starting over, but you're getting ATP out of that process and it's enough to keep the cell alive for a while.

48 minutes 53 seconds

In muscles, it's enough for you to give you a burst of energy for a while.

48 minutes 56 seconds

But eventually, eventually you'll still fatigue.

48 minutes 58 seconds

When you're talking about a single celled Organism, it's sort of enough for them to limp along as long as the Sugar's present and as long as they're recycling NAD plus they can keep doing this and producing ATP for themselves.

49 minutes 9 seconds

But it's, it's a, it's a bit of a slower process.

49 minutes 12 seconds

Now, some organisms are forced to do this.

49 minutes 15 seconds

So obligate anaerobes, remember, anaerobic is against oxygen.

49 minutes 19 seconds

The ones that are obligate anaerobes are forced to do this 'cause they live in anaerobic conditions or they have to have another carrier at the end of the electron transport chain, like nitrogen, and they tend to be poisoned by oxygen.

49 minutes 32 seconds

There's plenty of organisms that live in environments where oxygen is disruptive and poisonous.

49 minutes 38 seconds

And we find these things often in environments we would inspect like expect like stagnant ponds that don't smell very good deep in the soil where there's not going to be rich amounts of oxygen.

49 minutes 48 seconds

But there's ton of nitrogen because there's a bunch of nitrogen fixing bacteria in the soil and also in your gut.

49 minutes 55 seconds

And then facultative anaerobes can exist and do ATP production in the presence of oxygen, but can also switch to make ATP using fermentation or by doing oxidative phosphorylation.

50 minutes 30 seconds

It's also for things like baking bread.

50 minutes 33 seconds

There's lots of other fermented types of foods that will use microbes to produce a gas, like the bubbles that occur in a loaf of bread tend to happen from anaerobes doing fermentation.

50 minutes 45 seconds

And then lastly, I just want to connect these together as necessary and complementary means for being able to derive energy from organic molecules so that you can replenish your cellular energetic currency.

50 minutes 58 seconds

You can make lots of ATP in order to buy lots of metabolic processes that are required.

51 minutes 4 seconds

And so we use lots of different kinds of organic molecules for cellular respiration.

51 minutes 9 seconds

We focus largely on sugars.

51 minutes 11 seconds

They tend to be one of the easiest to break down.

51 minutes 14 seconds

We just don't get quite as much energy from sugars as we do from fats.

51 minutes 18 seconds

For example, glucose is very common.

51 minutes 21 seconds

In fact, our diet has been modified since World War Two to be very carbohydrate heavy, which is probably as we've seen by people's weight and also the amount of type 2 diabetes that's present and the other disorders that come with high carbohydrate diets is not the healthiest thing for us.

51 minutes 40 seconds

Whereas if we look at our ancestors, they probably spent a little bit more time getting fat in their body.

51 minutes 47 seconds

They might have gotten a little bit more lard from animals or animal fats or plant fats that you can eat less of but get more energy out of.

51 minutes 56 seconds

So fats contain way more hydrocarbon bonds, carbon, hydrogen bonds and atoms.

52 minutes 2 seconds

That way you get a lot more energy rich electrons from them and you can get twice as much ATP per gram as a gram of carbohydrate.

52 minutes 10 seconds

And This is why people who shift their diets to have slightly more fat and less carbohydrates, which sounds horrible.

52 minutes 16 seconds

We've been taught that it's horrible to eat fat in your diet, which is not completely true.

52 minutes 20 seconds

They tend to metabolize not only those fats, but the fat they already have also by training their body to do so.

52 minutes 27 seconds

And then you can consume less because if you can get twice as much ATP in a gram of fats in grams in a gram of fat, you don't need to consume as much to get as much energy.

52 minutes 36 seconds

And so that actually does cause individuals to lose weight when they readjust their carbohydrates lower to their fats a little higher and they need to be good fats too.

52 minutes 45 seconds

You can't just live on, you know, bacon and cheese cause it's also cholesterol issues involved in animal fats.

52 minutes 52 seconds

So you have to be careful.

52 minutes 53 seconds

It's actually good to get a lot of plant fats in your diet.

52 minutes 56 seconds

And then we can use proteins for fuel, but that's not the best way to do that.

53 minutes 1 second

Remember that proteins, the the building blocks of amino acid, are amino acids and they have N, nitrogen, carbon, carbon.

53 minutes 8 seconds

There's not really enough electrons to steal for us from proteins.

53 minutes 13 seconds

And that can actually kind of stress out your liver by trying to metabolize only protein.

53 minutes 18 seconds

So it's not healthy to have an all protein diet.

53 minutes 21 seconds

You need to choose some carbs or you need to choose some fats, and protein should kind of be in the middle.

53 minutes 26 seconds

Protein is more for building blocks, less for metabolizing.

53 minutes 30 seconds

And then so this is just sort of showing how these can all be fed into similar pathways.

53 minutes 34 seconds

You can break down sugars using glycolysis and into acetyl COA and feed it into the citric acid cycle.

53 minutes 39 seconds

Fats can be broken down into fatty acids and the same thing can occur.

53 minutes 43 seconds

You just sort of chop them up and they can be converted into G3P and then acetyl COA and go right into the citric acid cycle.

53 minutes 51 seconds

So you see that you're still deriving ATP in a similar mechanism but a slightly different offshoot.

53 minutes 57 seconds

If you consume more fats and less carbohydrates, when you also consume a higher fat diet and a lower carb diet, you can sustain that energy a lot longer.

54 minutes 7 seconds

You know that feeling during the day when you're like, oh, I'm crashing, I need to go eat some carbs because you've burned through your carbs so quickly.

54 minutes 13 seconds

But you won't use your reserve of carbohydrates in your kidney.

54 minutes 15 seconds

Really.

54 minutes 16 seconds

If you consume fats, you don't burn through it as quickly, but then your body will convert to the fat you already have and metabolize that.

54 minutes 24 seconds

And so you don't get hungry as quickly.

54 minutes 25 seconds

You don't have the shakes, you don't feel like you're crashing.

54 minutes 28 seconds

I can say from experience that that particular way of eating actually makes you feel pretty good.

54 minutes 33 seconds

You very well slept, you're super energized, and we should all consider that type of diet.

54 minutes 40 seconds

And then proteins also can be used in the citric acid cycle, but those are not the best type of fuel.

54 minutes 45 seconds

It's not preferred for your body's.

54 minutes 47 seconds

Either way, whatever organic molecules you're taking from your food are the raw materials that you need for basic biosynthesis of all the other things your cells require.

54 minutes 56 seconds

These are primary metabolites that you break down in order to build everything that you need.

55 minutes 2 seconds

And that also requires fundamentally ATP because remember, building things bigger than the sum of the parts it requires is an investment of energy and requires work because you're decreasing entropy by organizing things.

55 minutes 13 seconds

And so the food that you take in from the environment, which as we've already learned, is largely dependent on solar energy that's converted through plants into chemical energy that many organisms consume in order to derive ATP for their own needs.

55 minutes 28 seconds

And so this sort of ties together not only metabolism of proteins, fats and carbohydrates, but also this need to be able to do fermentation just in case conditions aren't right or you require metabolism in the absence of oxygen.

55 minutes 42 seconds

And so these things are definitely complementary to each other.

55 minutes 45 seconds

We otherwise we would not be able to derive energy from our environment as we are not photosynthetic.

55 minutes 52 seconds

We are the heterotrophs that must consume other things.

55 minutes 55 seconds

And so all these processes are absolutely necessary for deriving energy from your organic molecules.

56 minutes 1 second

Thank you so much for your attention, not only this lecture, but across both lectures and thinking about cellular respiration.

56 minutes 6 seconds

This is a challenging set of metabolic pathways for everybody the first time they learn it.

56 minutes 11 seconds

But if you see the value and you recognize the different parts and what work what, what's happening and what's required and what you get out of them, and then you paint a larger picture of what's happening in every mitochondria and in every cell in your body, you really start to recognize the importance of this.

56 minutes 27 seconds

And then thinking about it from the other end, thinking about what happens if you run out of fuel or if something blocks your electron transport chain and you can't do it anymore, you can't produce ATP anymore.

56 minutes 36 seconds

What the ultimate and very immediate outcome of the consequences of that actually are.

56 minutes 42 seconds

You start to recognize how important this pathway is.

56 minutes 45 seconds

Learn to love it, get familiar with it.

56 minutes 47 seconds

Recognize that later when you take biochemistry and Physiology classes, you might have to sort of understand the additional enzymes involved in cellular respiration or the consequences of what happens if the machinery breaks.

56 minutes 59 seconds

Until then, I, I hope you learned something new.

57 minutes 2 seconds

I hope you find the the necessity and the coolness in it, even if it is really challenging.

57 minutes 8 seconds

And until next time, I hope you have a wonderful day and you'll all be hearing from me again soon.