Note
Studied by 19 people
Lecture 12: Cellular Respiration 1
0 minutes 1 second
Hi everyone.
0 minutes 2 seconds
Welcome to your online lecture for today where we're going to be continuing our discussion of metabolism to include the heterotrophs like yourself.
0 minutes 11 seconds
We're going to focus on cellular respiration and we're going to do this in two parts.
0 minutes 16 seconds
And what we're really focusing on is how it is that cells in heterotrophs, like you have to harvest the chemical energy out of organic molecules that autotrophs, like plants and other photosynthetic things, actually produce for us to use.
0 minutes 33 seconds
Technically, they're producing them for themselves, but we take advantage of the fact because we need some carbon sources, usually in the form of sugars and fats and sometimes amino acids to be able to metabolize so that we can get an electrons that can do work for us.
0 minutes 50 seconds
Now, many of the carbohydrates that we take in unfortunately end up getting converted into fat here, which is the joke of the Beatrice the Biologist cartoon, because the fat cells think that we should keep it all 'cause we might need it all someday.
1 minute 5 seconds
And that's kind of the unfortunate consequence of how much we consume and how we don't use all of it for cellular respiration in this particular lecture, because it's kind of heavy and it's it's content that tends to confuse people and feels like a lot of steps and a lot of moving parts and a lot of things that you need to to memorize, which is better if you actually understand it.
1 minute 28 seconds
I tried to keep it light by introducing some of my favorite characters from one of the oldest, longest running sitcoms in history, namely The Simpsons, in particular, Homer Simpson, partly because Homer Simpson loves the sugary treat, particularly Donuts.
1 minute 48 seconds
And then as we see after we talk about cellular respiration, we think about fermentation.
1 minute 52 seconds
Fermentation is another process by which we can harvest chemical energy in the short term, and that's a means by which one of Homer Simpson's other favorite digestible items is produced.
2 minutes 6 seconds
Beer is made by fermentation.
2 minutes 8 seconds
And so Homer just seems like a really great subject for studying cellular respiration.
2 minutes 13 seconds
And I'm a child of the 80s and the 90s and Simpsons, we're very popular, have been for many decades now.
2 minutes 19 seconds
And so when we think about cellular respiration, what we're really talking about is the chemical opposite of photosynthesis, breaking down the organic molecules, sugars, namely in the form of glucose and converting the stored energy in glucose into something that we can use, which is our cellular energy currency or ATP.
2 minutes 44 seconds
Now that being said, the chemical pathway is the reverse of photosynthesis.
2 minutes 49 seconds
The biochemical pathway is very different.
2 minutes 53 seconds
It happens in a completely different organelle with lots of different enzymes and substrates.
2 minutes 58 seconds
And so make sure you recognize that even though the chemical reaction seems a little misleading, it seems like the same thing backwards and forwards.
3 minutes 6 seconds
It is a little different in the processes by which both of those pathways happen.
3 minutes 11 seconds
Photosynthesis and cellular respiration are complementary to each other, but the ways that we've evolved to be able to do them are different.
3 minutes 19 seconds
So we're going to think about taking in organic molecules like sugar requiring oxygen as an electron acceptor.
3 minutes 28 seconds
That gets reduced ultimately in the process after we've oxidized the sugar molecule down into waste products that are unusable for us, namely carbon dioxide and water, but also producing energy as a byproduct.
3 minutes 42 seconds
And we're going to see the energy that we get out of the sugar molecule directly is going to be electrons.
3 minutes 48 seconds
Electrons will do the work for us of producing ATP molecules that we're going to use for lots of cellular processes to maintain our energy budget.
3 minutes 58 seconds
And so photosynthesis, as we've already talked about in cellular respiration, really are the processes that are providing any energy for our lives.
4 minutes 6 seconds
Because remember what I told you, staying alive takes work.
4 minutes 10 seconds
And so in our ecosystems across the planet, energy first and foremost comes from the sun.
4 minutes 17 seconds
There's all kinds of solar energy hitting the planet, most of which we can't even actually use.
4 minutes 23 seconds
Plants are able to harvest about 1% of the energy that's actually hitting the surface of the planet.
4 minutes 28 seconds
And by plants, I'm including all the other photosynthetic things on the planet as well, which is actually overwhelmingly represented by the top 200 meters of all of the world's oceans, much more so than any terrestrial environment.
4 minutes 43 seconds
And so photosynthesis, as we learned, is where solar energy is captured by pigments and chloroplasts that excite those pigments to donate electrons that are generally stripped away from water molecules and bring in carbon dioxide gas and use those electrons to link carbon molecules together and build larger structures in the form of sugar.
5 minutes 4 seconds
And so the products of this process are going to be carbohydrates and oxygen, molecular oxygen as waste, which is super useful for us because molecular oxygen is one of the reactants that we need in order to do cellular respiration.
5 minutes 19 seconds
So we take in sugar as a reactant.
5 minutes 21 seconds
We use oxygen in order to combust this sugar.
5 minutes 26 seconds
In reality, oxygen becomes the ultimate electron receptor that is going to be reduced in the whole process.
5 minutes 33 seconds
And we end up releasing carbon dioxide and water as waste.
5 minutes 36 seconds
And carbon dioxide is easy to get rid of because it's a gas that is happy to get out of our cells and we're water based organisms anyway, so water as a waste product doesn't really hurt us too much.
5 minutes 46 seconds
We require lots and lots of mitochondria to be able to do this.
5 minutes 50 seconds
We're going to see this is the organelle of choice that is for completing cellular respiration.
5 minutes 55 seconds
We'll also see a small part of it happens in the cytoplasm, but largely the bulk of it occurs in these specialized organelles that have evolved from alpha proteobacteria that were ingested billions of years ago and maintained in this, in this context inside of eukaryotic cells.
6 minutes 15 seconds
And as any energetic metabolic process includes, some of this energy that we do is going to be lost to the form of heat because nothing is totally efficient when it comes to metabolizing organic molecules.
6 minutes 28 seconds
And so our cells are meant to use the mitochondria, chloroplasts or the use the cytosol, the and, and mitochondria and the enzymes that are present in those to basically combust sugars.
6 minutes 43 seconds
Now, it's not burning sugar in the sense of, you know, you put it on a stove and you melt it in a pot.
6 minutes 48 seconds
It's not exactly like that, but it is still a combustion process where oxygen is actually used to break apart glucose molecules.
6 minutes 56 seconds
Now the chemical reaction, as I mentioned, is a little bit misleading.
6 minutes 59 seconds
Once you see the biochemical process and the the the whole sum of steps for how this works, it starts to make a lot more sense why oxygen is involved.
7 minutes 9 seconds
It's because it is one of the most electronegatively stingy things that is very readily abundant in our cells and is going to be the ultimate guy at the end of the whole process that catches our tired electrons after we've used them to do a bunch of work.
7 minutes 24 seconds
And where do those electrons come from, Right?
7 minutes 26 seconds
They come from that sugar molecule.
7 minutes 28 seconds
They're hidden in the bonds between the carbons and between the carbons and hydrogens.
7 minutes 33 seconds
And we're going to break apart that molecule and we're going to use those electrons to do work for us.
7 minutes 38 seconds
OK.
7 minutes 38 seconds
So keep in mind this particular reaction, glucose combusted with oxygen.
7 minutes 43 seconds
Black arrow, black arrow, black arrow, big black box of stuff that happens in the middle gives us multiple molecules of carbon dioxide which have been separated from each other.
7 minutes 54 seconds
They were initially stuck together in that glucose molecule and a couple of molecules of water.
8 minutes
And so this is the opposite of photosynthesis, right?
8 minutes 2 seconds
Where you're using carbon dioxide and you're stripping electrons out of water in order to build sugar and oxygen.
8 minutes 8 seconds
And in this case, instead of utilizing ATP, we're going to produce ATP because this is a process where it's going to be exergonic.
8 minutes 16 seconds
You're going to break that molecule apart and release the energy stored in it, or use the release energy to create another form of energy, transforming it to something else, which is ATP.
8 minutes 27 seconds
Remember that in photosynthesis, the opposite is endergonic.
8 minutes 31 seconds
In order to build something much more complex and larger than the sum of the parts, it requires an investment of energy, which is why photosystem 2 has to make ATP first before the Calvin cycle can proceed.
8 minutes 42 seconds
Requires work when you're decreasing entropy, making less chaos in a system.
8 minutes 47 seconds
And so oxygen's involvement in this comes from its strong electronegativity.
8 minutes 52 seconds
That's really electrons stingy and it's actually going to help sort of vacuum electrons all the way through the part of this process that's making the bulk of the ATP in our mitochondria.
9 minutes 6 seconds
Remember that electrons are excitable, but as they do work, they tend to get tired, they tend to get worn out, they get jumped up to that high energy state.
9 minutes 17 seconds
It gets them to do work and then they sort of get tired and they either have to be collected by something and used in a bond or they have to be re excited in order to do that work again.
9 minutes 26 seconds
Remember we don't lose or or dispose of electrons.
9 minutes 30 seconds
We always catch and recycle them.
9 minutes 33 seconds
They always end up in some molecule.
9 minutes 35 seconds
And that's because electrons are super reactive and we don't want them to end up in the wrong place.
9 minutes 41 seconds
Like oxygen alone, right?
9 minutes 43 seconds
Oxygen alone, hanging out with some electrons is bad.
9 minutes 46 seconds
It's very, very interactive.
9 minutes 47 seconds
That's what we call reactive oxygen, and we know it's really damaging to our DNA and our proteins.
9 minutes 53 seconds
So what we do is try to guarantee that if we hand off electrons to oxygen at the end, we also give it some protons to neutralize it into actual water, which is harmless for us.
10 minutes 3 seconds
But the process of utilizing the electrons that are stored in the bonds of glucose and getting them to do work is imagining that as they get tired, they're sort of free falling down an energy hill, right?
10 minutes 14 seconds
And so here we've got our friend Lisa Simpson and her friend Ralph Wiggum.
10 minutes 17 seconds
And Ralph is rolling down a hill, right?
10 minutes 19 seconds
So he's got real high potential energy as he's starting at the top of the hill, and that transfers into kinetic energy.
10 minutes 24 seconds
And then as he gets to the bottom of the hill, most of the energy is gone.
10 minutes 27 seconds
And so electrons experience this as they move through the part of the pathway that they're involved in through their work, which ultimately results in the production of ATP.
10 minutes 37 seconds
And so remember, it's this process of sort of falling down a hill as they run out of energy.
10 minutes 41 seconds
And so we can use the chemical bonds that are present in glucose and convert them into chemical bonds that are present in ATP, which we actually use in our cells.
10 minutes 53 seconds
Something to remember as an aside before we continue thinking about cellular respiration.
10 minutes 58 seconds
Cellular respiration is not the same thing as anatomical or physiological respiration, as UN breathing in and out.
11 minutes 5 seconds
Not the exact same thing.
11 minutes 7 seconds
And all organisms are gonna respire in some way.
11 minutes 10 seconds
Anybody doing cellular respiration, even plants, do cellular respiration.
11 minutes 15 seconds
They have to metabolize sugars for their own processes of growth and building things and responding to their environment.
11 minutes 22 seconds
And they don't have lungs, but they're still doing cellular respiration.
11 minutes 26 seconds
When we think about respiration in terms of us as air breathers, that's often what we're talking about, is lung breathing.
11 minutes 34 seconds
This is cellular respiration.
11 minutes 36 seconds
And so this is a little different.
11 minutes 38 seconds
This is where we think about using oxygen for an actual process, a metabolic process.
11 minutes 45 seconds
When we think of breathing respiration, that's where we're exchanging gases through our lungs.
11 minutes 51 seconds
We bring in oxygen, re release CO2.
11 minutes 54 seconds
That process is supporting cellular respiration on the cell level.
11 minutes 59 seconds
OK, But actual breathing respiration and cellular respiration are two different processes that we're talking about.
12 minutes 5 seconds
That eventually breathing respiration actually feeds into cellular respiration.
12 minutes 11 seconds
As you're bringing in oxygen from your external environment, you use it in cellular respiration.
12 minutes 15 seconds
As you produce CO2 waste in cellular respiration, you release it to the environment by actually breathing.
12 minutes 21 seconds
So later we're going to talk about the respiratory system and the circulatory system, and we will address breathing respiration later.
12 minutes 28 seconds
Just remember to keep those two things straight for now.
12 minutes 31 seconds
And so cells are going to capture energy from electrons that are stripped out of organic molecules that go through a series of steps to do work and are ultimately going to hand it be handed off to oxygen at the end.
12 minutes 43 seconds
And so glucose is the one that loses its hydrogen atoms because that's where the electrons are being stored.
12 minutes 50 seconds
And it's going to become oxidized.
12 minutes 53 seconds
And so by losing its electrons, remember, it's going to be oxidized.
12 minutes 56 seconds
If it gained electrons like carbon dioxide does in photosynthesis, that's making it reduced.
13 minutes 3 seconds
OK, So here we're stripping the the hydrogen atoms.
13 minutes 5 seconds
Here is glucose, C6H12O6.
13 minutes 8 seconds
Notice it's going to have its hydrogen atoms stripped, and look what it becomes.
13 minutes 12 seconds
It becomes carbon dioxide.
13 minutes 14 seconds
Where do those hydrogen atoms go?
13 minutes 16 seconds
Well, the only place to add them is on to the oxygen that it's starting with in the reactants.
13 minutes 21 seconds
And you'll notice that's what happens.
13 minutes 23 seconds
We end up adding the hydrogen atoms to the oxygen atoms to produce water, and so oxygen is going to gain those hydrogen atoms.
13 minutes 31 seconds
It's getting the electrons, which means that it's becoming reduced to convert it into actual water.
13 minutes 37 seconds
Remember always that inside of a hydrogen atom is one proton and one electron, and they're attracted to each other, and that is the simplest atom.
13 minutes 45 seconds
And so we hide electrons in hydrogen atoms because they're neutral and they're safe and they're not reactive and they don't change the pH of a solution.
13 minutes 54 seconds
So we hide them together.
13 minutes 56 seconds
And what we do is we move these HS around in reactions, and the electrons are hidden in those hydrogen atoms, but they're neutral and happy and satisfied and not reactive.
14 minutes 5 seconds
And so you're going to watch anywhere the HS go.
14 minutes 8 seconds
That's the thing that's being reduced to form a new product.
14 minutes 12 seconds
OK.
14 minutes 13 seconds
And so this gain of hydrogen atoms on oxygen causes it to form a new molecule.
14 minutes 18 seconds
And oxygen is being reduced in this process as expected, because it's the electronegatively stingy one, right?
14 minutes 23 seconds
So we're going to make sure we follow those.
14 minutes 26 seconds
So the steps of cellular respiration occur in three large parts.
14 minutes 31 seconds
We're going to break this particular lecture into two parts.
14 minutes 35 seconds
We're going to discuss the 1st 2 main parts of cellular respiration.
14 minutes 39 seconds
And then in the next small lecture, we're going to discuss the last part where there's a big payout of ATP production.
14 minutes 46 seconds
And we're going to talk very briefly about the process of fermentation, which is an offshoot of cellular respiration.
14 minutes 54 seconds
When conditions make it so that you can't compete the complete cellular respiration successfully, it's sort of a shorter way of maintaining your energy budget temporarily.
15 minutes 5 seconds
And so cellular respiration is combined of a series of reactions that ultimately produces ATP from an electron transport chain at the end.
15 minutes 15 seconds
And I want you, as we talk about this, to think about the similarities that we may have seen in the thylakoid membranes in chloroplasts.
15 minutes 23 seconds
And you'll look for very similar mechanistic commonalities between the two, OK?
15 minutes 29 seconds
It'll also make the differences pretty clear as well.
15 minutes 32 seconds
So cellular expiration has four steps, the first of which is called glycolysis.
15 minutes 36 seconds
And so that prefix glyco means sugar and lysis or to lysed something is to break it down, OK.
15 minutes 43 seconds
And so we've got a six carbon ring of glucose and we're going to break it down into two, three carbon molecules called pyruvate, OK?
15 minutes 53 seconds
This is a great overview slide.
15 minutes 55 seconds
This is something that as we add the parts to it, you should consider drawing it out so that in your motor memory you can recall these individual steps, what they're called, what they're producing, and then where everything is inside of the cell, 'cause you'll notice that this first part actually happens in the cytoplasm.
16 minutes 12 seconds
So it's not in the mitochondria yet, it happens out in the cytoplasm where we break it down into pyruvate.
16 minutes 18 seconds
And the next step is gonna be pyruvate processing.
16 minutes 21 seconds
We need to break that down.
16 minutes 22 seconds
One more step 'cause remember, the goal is to take these glucose molecules and break them apart, right, And steal the electrons that are holding the atoms together.
16 minutes 32 seconds
It's like taking a necklace with beads on it, getting rid of all the beads and taking the string, right?
16 minutes 38 seconds
It's taking the connections out.
16 minutes 39 seconds
And remember, every bond that we break is gonna have two electrons.
16 minutes 44 seconds
Every bond you break, every electron you take, it's going to have two electrons and a bond.
16 minutes 49 seconds
OK.
16 minutes 49 seconds
And so we're going to think about pyruvate processing next.
16 minutes 52 seconds
That's the three carbon, dude.
16 minutes 55 seconds
That glucose is going to be broken down into two of those.
16 minutes 58 seconds
Pyruvate is then going to travel into the mitochondria through a transporter and there it's going to be modified or oxidized, which means we're going to steal some more electrons from it, break one more bond, and we're going to convert it into A2 carbon thing called acetyl COA.
17 minutes 15 seconds
Acetyl COA is then going to be fed into a cycle called the citric acid cycle, which kind of resembles the Calvin cycle a bit in the way that it's run mostly different intermediates.
17 minutes 30 seconds
Couple of intermediates are the same and it's going to be oxidized further down.
17 minutes 34 seconds
The whole goal is to take the six carbon ring and break it apart into individual carbon dioxide molecules.
17 minutes 40 seconds
And everything that comes out of these three separate subparts is going to end up going to the last main part.
17 minutes 49 seconds
I guess it's actually really 4 reactions, 4, four major steps.
17 minutes 53 seconds
Those are going to end up going to an electron transport chain and doing a process called oxidative phosphorylation.
18 minutes 1 second
OK.
18 minutes 1 second
So oxidation is stealing electrons and phosphorylation is adding phosphates to things.
18 minutes 8 seconds
And so it would make sense that and we're adding phosphates to things.
18 minutes 11 seconds
We're making a product ATP that has phosphates on it.
18 minutes 15 seconds
OK.
18 minutes 16 seconds
And so we're going to think about each step of this and what we glean from each step and where do they go to drive this process at the end, all the while remembering that this is happening inside of your cells right now.
18 minutes 27 seconds
So First things first, sugar breaking.
18 minutes 29 seconds
We have our friend Homer here eating a doughnut appropriate that he's about to do some glycolysis with it in his mitochondria.
18 minutes 35 seconds
So remember that prefix glyco means sugar and lysis means breaking.
18 minutes 38 seconds
And so that's what we're going to do.
18 minutes 40 seconds
We're going to take sugar molecule and we're going to break it apart in half, OK.
18 minutes 43 seconds
And so a lot of this begins in your digestive tract.
18 minutes 47 seconds
We're going to learn a little later when we talk about nutrition and digestion that the breakdown of carbohydrates tends to start in your mouth.
18 minutes 55 seconds
But as it goes through your stomach and into your intestinal tract, that's where a lot of those sugars are going to be absorbed into your cells.
19 minutes 1 second
And then your cells are going to transport those sugar molecules in to the cytoplasm and start breaking them down.
19 minutes 8 seconds
OK.
19 minutes 8 seconds
And there's a series of about 10 reactions.
19 minutes 10 seconds
I want you to understand what's happening here in a broad overview.
19 minutes 14 seconds
I don't want you to memorize any structures.
19 minutes 16 seconds
I do want you to think about what's consumed and what's produced.
19 minutes 19 seconds
But if we sort of walk through stepwise and then maybe we watch sort of a summary video of what happens, it'll become clear these particular pathways are going to come across your desk again.
19 minutes 29 seconds
If you take biochemistry later, you're really going to talk about these a lot.
19 minutes 32 seconds
Probably also if you take anatomy and Physiology and then later maybe in cell bio, if you learn, if you take cell bio, you might learn this again.
19 minutes 41 seconds
But it becomes important later to understand how this process works so that you can think backwards about what happens when this process goes wrong.
19 minutes 50 seconds
What happens when you're not able to breakdown sugars?
19 minutes 52 seconds
What happens if you have a mutation in one of the enzymes in these pathways?
19 minutes 55 seconds
And so it's having a good strong foundation for all the parts of cellular respiration is really important.
20 minutes
And the more you work on it in this class, the better you're going to feel about it later.
20 minutes 5 seconds
OK, so sugar breakdown, we're going to see that we have three or two, two main phases for being able to breakdown sugar.
20 minutes 11 seconds
And this is going to happen in the cytoplasm.
20 minutes 13 seconds
The first is using a little bit of energy to modify glucose and make it unstable and then start breaking apart, and then take some of those resources back to make additional energy.
20 minutes 29 seconds
When you see these numbers, it seems kind of weird, but when you see the actual pathway, you'll understand.
20 minutes 34 seconds
In most businesses, you gotta invest a little money to make a little money, right?
20 minutes 38 seconds
And the same thing is true of glycolysis.
20 minutes 40 seconds
You have to invest a little bit of ATP in an energy investment phase to modify glucose to make it unstable, and then take a bunch of phosphates back again and make some additional ATP that you didn't even start with.
20 minutes 51 seconds
So you're investing 2 and you're making four, which means you're netting 2 that you didn't have when you started.
20 minutes 57 seconds
So we're going to talk about not only how we produce a tiny bit of ATP, not enough to keep you alive, just enough for, you know, chemical purposes using phosphates, but we're also going to talk about how we're going to start stealing electrons by breaking apart sugar molecules.
21 minutes 11 seconds
In the very first step, what we're going to do is we're going to take electrons by breaking their bonds.
21 minutes 16 seconds
We're going to hand them off to an electron carrier, and that electron carrier is going to go off to the electron transport chain.
21 minutes 22 seconds
It's very similar to what we saw in photosynthesis where we take electrons, we hand it off to something that is easily reduced but happy to be oxidized when it gets to where it's going, something that'll hold it for a while, but not stingy enough to keep your electrons.
21 minutes 36 seconds
OK.
21 minutes 36 seconds
And then we're going to think about the next steps after that.
21 minutes 39 seconds
So Glysis is consisting of those two phase.
21 minutes 42 seconds
First you have to pay off pay in a little energy, but you're going to get that back and two more.
21 minutes 47 seconds
So there's a little bit of a payoff, and that's simply because of how we're trying to modify glucose in order to begin the process of trapping it in a cell and breaking it down by oxidizing its bonds.
21 minutes 59 seconds
And so this is our electron carrier, NAD Plus.
22 minutes 2 seconds
You may remember when I talked about metabolism, I showed you that NAD plus can hold two electrons, one on a nitrogen atom and one on a carbon atom, and will hold them temporarily until they can be handed off to an electron transport chain because they're actually more stable as NAD plus than they are holding extra electrons.
22 minutes 22 seconds
So remember that if you give NAD Plus one electron, it becomes just plain NAD.
22 minutes 27 seconds
If you give it a second electron, it becomes NAD minus.
22 minutes 31 seconds
That makes it reactive.
22 minutes 32 seconds
And we don't want that to be the case.
22 minutes 34 seconds
So we're also going to give it a proton and it just becomes regular old stable NADH, hiding two electrons, but not really wanting to go out and interact with anybody.
22 minutes 44 seconds
OK, so this is the first thing that happens.
22 minutes 46 seconds
And this is where you're going to be like, there's too much chemistry in my biology, but you just kind of have to recognize it's a metabolic pathway.
22 minutes 53 seconds
Every enzyme that's involved is going to help trap and start converting and making these sugar molecules unstable so that they can be broken in two halves, OK.
23 minutes 4 seconds
And so here's our glucose molecule.
23 minutes 6 seconds
We've got 123456 carbons.
23 minutes 11 seconds
And what we're kind of going to do is we're going to end up breaking the molecule sort of across in half.
23 minutes 15 seconds
So we have 3 carbons and three carbons, and the products are just a tiny bit different from each other.
23 minutes 20 seconds
But we'll notice that we end with a molecule G3P, which is very similar.
23 minutes 25 seconds
That was what was produced in photosynthesis in the Calvin cycle.
23 minutes 28 seconds
Remember 1/2 a sugar, right?
23 minutes 31 seconds
OK, so the first thing that happens here is the very first enzyme is going to be hexokinase.
23 minutes 34 seconds
Look at the name.
23 minutes 35 seconds
HEXO means 6 kinase, means I had phosphates to things, and so it's going to take this 6 carbon sugar and it's going to remove a phosphate off of ATP and it's going to phosphorylate the sugar right here on the 6th carbon, making glucose 6 phosphate.
23 minutes 52 seconds
See the name.
23 minutes 53 seconds
It tells you exactly what happened.
23 minutes 55 seconds
And the reason that it does that is to trap glucose in your cells, like the lining of your intestines and convert it into something slightly different than regular glucose.
24 minutes 5 seconds
So it always seems like, well, the glucose is all gone.
24 minutes 8 seconds
We used it all, but in really you just converted it into something else that can't get back out of your cells and looks like makes it look like your glucose levels are low.
24 minutes 17 seconds
So you'll just keep bringing more into the cells.
24 minutes 20 seconds
OK.
24 minutes 20 seconds
And then what's going to happen is a slight little rearrangement here.
24 minutes 24 seconds
We're going to have phosphogluco isomerase.
24 minutes 27 seconds
We're going to see that we're going to make it look like a pentose ring now instead of a hexo spring.
24 minutes 31 seconds
And we've got these same groups that are on either end.
24 minutes 35 seconds
And to balance it out, we're going to use phospho fructokinase because of this is now fructose.
24 minutes 41 seconds
Remember, when you have glucose, it's or, or sucrose, it's glucose and fructose.
24 minutes 45 seconds
So it's easy to convert glucose into fructose if you just move the molecule around a little and make it A5 carbon sugar.
24 minutes 52 seconds
And so we're going to end up phosphorylating it again so that it's even on both sides.
24 minutes 56 seconds
And then we're going to end up breaking this in a slightly unequal halves, OK.
25 minutes 1 second
And so here's your investment of two phosphates.
25 minutes 4 seconds
The 1st is to trap it in the cell.
25 minutes 6 seconds
The second are to help make it unstable.
25 minutes 9 seconds
And so we're not trying to add additional functional groups to this molecule as we break it down.
25 minutes 15 seconds
Those phosphates are only temporary.
25 minutes 17 seconds
They're just kind of like placeholders for the enzymes to get a hold of the molecule and start pulling it apart.
25 minutes 23 seconds
Eventually those phosphates get taken right back off and put right back onto ADP to make more ATP.
25 minutes 28 seconds
They get recycled.
25 minutes 29 seconds
We're trying to break this down into smaller bits, not make bigger ones.
25 minutes 33 seconds
And so this enzyme called aldolase is going to end up breaking this fructose 16 biphosphate bisphosphate.
25 minutes 40 seconds
Notice it's on the one in the six carbon.
25 minutes 42 seconds
There's phosphates on both.
25 minutes 43 seconds
That's the name.
25 minutes 44 seconds
It's going to break it in half into two different types, glyceraldehyde 3 phosphate, it's still 1 phosphate and dihydroxyacetone phosphate, D HAP.
25 minutes 54 seconds
Now they're very similar to each other, but they can be interconverted back and forth depending on the presence of an isomerase, right?
26 minutes
And so we're probably going to end up using G3 PA lot more than DHAP because we want two starting molecules that are the same going into the energy payoff phase to make pyruvate.
26 minutes 11 seconds
We don't want to have to rescramble and do a different set of biochemical reactions to make the same thing.
26 minutes 17 seconds
So we're going to convert D AAP into G3P, and we got two molecules of that.
26 minutes 21 seconds
So we took a six carbon ring and broke it into two halves.
26 minutes 25 seconds
In that case, how many bonds did we break?
26 minutes 29 seconds
Did we get anything out of that?
26 minutes 31 seconds
We ended up breaking a couple of bonds, didn't we?
26 minutes 35 seconds
Yeah, we break A6 carbon thing into two halves.
26 minutes 38 seconds
We broke a bond here and a bond here.
26 minutes 40 seconds
So we broke two bonds.
26 minutes 42 seconds
Right now we're going to see that we're going to scavenge some electrons off of this molecule using this trios phosphate dehydrogenase.
26 minutes 51 seconds
Look at the name.
26 minutes 52 seconds
Triose is 3 sugar, 3 carbon sugar phosphate.
26 minutes 58 seconds
I'm using inorganic phosphate to do my work dehydrogenase.
27 minutes 4 seconds
I am taking hydrogen atoms off of this thing so I can steal electrons.
27 minutes 13 seconds
Now watch what happens.
27 minutes 14 seconds
So notice this H right here, it's got an electron in it, right?
27 minutes 18 seconds
And there's two molecules of this.
27 minutes 20 seconds
I'm going to steal and swap it with a phosphate PO4 to satisfy this carbon because it's got to have a placeholder.
27 minutes 29 seconds
I can't just leave it unbonded.
27 minutes 31 seconds
And that doesn't work.
27 minutes 32 seconds
But I've steal this H and I give do it twice.
27 minutes 35 seconds
I give the electrons actually looks like I'm doing it four times.
27 minutes 39 seconds
No two molecule.
27 minutes 42 seconds
Yeah, that's right.
27 minutes 44 seconds
I'm going to steal this these hydrogen atoms off of G3P and I'm going to hand them over to NADH and it's going to give me this right here, this one, three bisphosphate glycerate, bisphosphoglycerate.
27 minutes 55 seconds
So glycerate is a derivative of glyceraldehyde.
27 minutes 58 seconds
Now it's phosphorylated twice.
27 minutes 59 seconds
We don't want that.
28 minutes
We want to take those phosphate residues back and put them back onto ADP.
28 minutes 6 seconds
OK.
28 minutes 6 seconds
And we're aligning ourselves to create carboxyl groups on this sugar intermediate that are easy to like, chop off and release as CO2 later.
28 minutes 15 seconds
Do you see this right here?
28 minutes 17 seconds
COO, This looks like a good place to go break a bond, release CO2.
28 minutes 21 seconds
So we're, our cells are arranging these molecules to get prepared to broken down even further.
28 minutes 27 seconds
So we're gonna remove these phosphates off here, give them to ADP, and there's our first ATP back.
28 minutes 32 seconds
Now we're net neutral 'cause that's what we've invested.
28 minutes 36 seconds
And that enzyme, phosphoglycerokinase, is going to add another phosphate residue.
28 minutes 42 seconds
Actually, let's see, are we going to take him off glycerokinase?
28 minutes 46 seconds
He's phosphorylating ADP, that's why.
28 minutes 49 seconds
Yeah, so he's a kinase, phosphoglycerokinase.
28 minutes 51 seconds
He's not phosphorylating glycerate.
28 minutes 53 seconds
He's removing phosphates and adding in the back onto ADP to end up making three phosphoglycerate.
29 minutes
OK, not by phosphoglycerate, just single phosphoglycerate.
29 minutes 3 seconds
So he's taking those off 2, two of the two molecules and leaving this one right here.
29 minutes 7 seconds
And then phosphoglyceramutase.
29 minutes 9 seconds
This is just up swapping it around.
29 minutes 12 seconds
I'm swapping that phosphate up here to get this down here so I can steal the hydroxyl group and force a double bond over here.
29 minutes 21 seconds
So I'm going to convert this guy phosphoglycerate into phosphoenolpyruvate.
29 minutes 25 seconds
This is actually a really, really important three carbon intermediate that's present in lots of organisms.
29 minutes 30 seconds
Plants use this too.
29 minutes 32 seconds
This trio, sugar PEP, this is a good intermediate and lots of pathways, particularly if you're converting back and forth.
29 minutes 38 seconds
Pyruvate.
29 minutes 39 seconds
So enolace is gonna end up removing 2 water molecules.
29 minutes 42 seconds
So we're gonna remove an OH from right here and we're gonna have, let's see it.
29 minutes 49 seconds
We're gonna have an OH, we're gonna remove the phosphate and move it up here.
29 minutes 54 seconds
And we've done some swapping, all right, but we're going to lose 2 water molecules from here to make PEP.
30 minutes 1 second
So look at the conversion.
30 minutes 2 seconds
We've got chapter 2.
30 minutes 3 seconds
We lost an oh right here.
30 minutes 5 seconds
And we've got a phosphate, but we lost the hydrogen atom on the other side and forced a double bond.
30 minutes 10 seconds
And so you snuck out a water molecule and and created phosphoenopyruvate.
30 minutes 16 seconds
Now you're already almost pyruvate.
30 minutes 19 seconds
See, it's in the name, but it's still phosphorylated and as an enol.
30 minutes 23 seconds
And you have to get rid of that phosphorylation.
30 minutes 26 seconds
And so pyruvate kinase is going to take that phosphate off, add it to ADP.
30 minutes 31 seconds
Now you got ATP and there's no more phosphates left, which is great.
30 minutes 35 seconds
So not only are there no more phosphates left, we've set this molecule up to sort of be ready to start chopping off more bonds.
30 minutes 43 seconds
Like this is a great place to start right here at the end, right?
30 minutes 46 seconds
If, if breaking this down and releasing CO2 gas is your goal, this is what it looks like.
30 minutes 51 seconds
This is how you could possibly set up and do this.
30 minutes 54 seconds
OK, so now we've got pyruvate actually produced.
30 minutes 58 seconds
Now, when that little bit of ATP is being produced in the payout phase, you have to recognize that you have some enzymes just kind of hanging out in your cytoplasm that are regenerating ATP one at a time by picking up ADP, adenosine diphosphate in an inorganic phosphate and smooshing them together and making ATP.
31 minutes 21 seconds
That's a real slow process, but it's like the scavenger, you know, picking these up and building them as needed to recycle phosphates.
31 minutes 30 seconds
But this is that was not enough to keep you alive, OK.
31 minutes 33 seconds
And so this is not the bulk of the ATP you would produce from this.
31 minutes 36 seconds
And so this is done by something called substrate level phosphorylation, which is like low level, low turn out regulation.
31 minutes 43 seconds
And so this here's an example where this is happening.
31 minutes 46 seconds
We're removing this phosphate off of this phosphoglycerate up here and we're adding it on the ADP to produce ATP.
31 minutes 53 seconds
And so that's what phosphoglycero kinase's job is, take it off of this thing we're breaking down and put it back on the ATP.
31 minutes 59 seconds
It's still transferring a phosphate, which is why it's a kinase.
32 minutes 1 second
But these enzymes, they end up localizing ADP.
32 minutes 7 seconds
Notice it's only got 2 phosphates on it, and they take that phosphorylated substrate like this guy, and they cut that off and transfer it onto ATP and they just get to regenerate ATP molecules, OK?
32 minutes 19 seconds
So you get a little bit of that along the way, but not the bulk of it.
32 minutes 23 seconds
So substrate level phosphorylation is low level here and there, a couple of instances that happen in glycolysis and the citric acid cycle.
32 minutes 31 seconds
But the real payout comes at this very, very end that we're going to talk about in the next lecture, which is oxidative phosphorylation.
32 minutes 38 seconds
This is literally stealing electrons to drive the work of phosphorylating large quantities of ADP into ATP.
32 minutes 50 seconds
So that requires an electron transport chain, which is at the very end of this well into the mitochondria.
32 minutes 56 seconds
That's the last step where most of the business is happening.
32 minutes 59 seconds
So we've broken apart our sugar molecule 6 carbons into 3 carbon halves, and we've phosphorylated them to destabilize them and start shifting around bonds.
33 minutes 11 seconds
And then we remove the phosphate residues at the end because we want them back.
33 minutes 15 seconds
And now we've moved bonds around and stolen some electrons to produce two pyruvate molecules.
33 minutes 22 seconds
So every six carbon sugar is going to be broken down and converted immediately into two three carbon pyruvate molecules.
33 minutes 30 seconds
This is all happening in a cytosol, which means the enzymes necessary for this are floating around in the cytoplasm.
33 minutes 36 seconds
Pyruvate is then going to be transported across the mitochondrial membranes to the inside matrix of the mitochondrian.
33 minutes 44 seconds
And that's where we're going to find not only that pyruvate gets oxidized a little further, which means it's going to have some electrons stolen.
33 minutes 52 seconds
But then we see that the product from that is going to feed into the citric acid cycle, all of the enzymes of which are necessary necessarily housed inside the matrix of the mitochondrian.
34 minutes 4 seconds
And so pyruvates to get the pyruvate gets transported into the mitochondrium.
34 minutes 11 seconds
And some of these electrons that are produced or some of these electrons that are stolen and given to NAD to carry are probably also going to be transported into the mitochondran.
34 minutes 21 seconds
Mitochondrion is going to need those electrons at the end of the pathway.
34 minutes 26 seconds
And it's evolved to have exchangers in the two membranes that allow it to move things in and out that it needs.
34 minutes 33 seconds
So for example, if you're moving NADH into the mitochondria and using it, you have to then swap some NAD plus back out so that it can be used in the cytoplasm.
34 minutes 44 seconds
If you're making ATP in the mitochondria, you have to, when you send it out to be used, you have to swap in ADP in inorganic phosphate.
34 minutes 53 seconds
Otherwise you can't keep making more ATP.
34 minutes 55 seconds
So they're exchangers that will bring in what's needed for building and send out what you've already made.
35 minutes 1 second
OK.
35 minutes 1 second
And so we're gonna see that these next steps actually happen in the mitochondrial matrix.
35 minutes 6 seconds
If you remember a little bit about the anatomy of a mitochondria and you'll remember that it has a whole bunch of internal folds that are inside of it, Lots and lots and lots of surface area of membranes so that you can support a lot of electron transport chain protein complexes, So you can make tons of ATP.
35 minutes 27 seconds
And remember around those membranous folds is going to be fluid that's very similar to the cytoplasm in our cells, but would have been the cytoplasm in the bacterial cell that this evolved from.
35 minutes 39 seconds
And so now we call it matrix instead of cytoplasm.
35 minutes 43 seconds
But all the enzymes necessary for pyruvate oxidation chopping it down a little further and the citric acid cycle chopping it down the rest of the way are present in the matrix, OK.
35 minutes 54 seconds
And so after that, it's going to head what the what's produced out of the citric acid cycle is going to end up heading to these individual little Christae where the complexes necessary to produce ATP are going to be present.
36 minutes 9 seconds
So remember, anytime we see a whole lot of membranes, what we're really trying to do is increase surface area.
36 minutes 14 seconds
We're trying to do a whole lot of business, a whole lot of ATP production in a very small space because your cells demand it.
36 minutes 23 seconds
OK, so now we're inside the matrix in the mitochondrium, and we're going to see that pyruvate is going to be oxidized.
36 minutes 29 seconds
Now, don't let yourself get confused about redox terms.
36 minutes 32 seconds
I know that remembering reduction in oxidation can be really confusing.
36 minutes 37 seconds
Oxidation is electron theft.
36 minutes 37 seconds
Oxidation is electron theft.
36 minutes 40 seconds
OK.
36 minutes 41 seconds
Remember, the goal here is to take these carbon molecules and break them apart, to steal the electrons in their bonds, as well as the ones between the hydrogen atoms that are in some of them as well.
36 minutes 54 seconds
And so oxidation is breaking things down.
36 minutes 57 seconds
When you reduce something, you're giving it electrons, which means you're building it up, you're creating bonds.
37 minutes 2 seconds
And so after glycolysis, we're going to see pyruvate is going to be the next target, OK.
37 minutes 10 seconds
And so pyruvate is going to be transported across both membranes of the mitochondrion, the outer and inner membrane, and past the intermembrane space.
37 minutes 20 seconds
And it's going to end up going into the mitochondrial matrix, OK.
37 minutes 24 seconds
And so these Gray balls represent carbon atoms.
37 minutes 27 seconds
This is a simplified version of thinking about breaking down an organic thing, A3 carbon sugar, called a triose.
37 minutes 34 seconds
The enzymes necessary for doing it are present in the mitochondrial matrix.
37 minutes 38 seconds
And so remember that we've set up pyruvate to be ready to just chop off the end and that becomes our first CO2 that we can lose from every single pyruvate.
37 minutes 50 seconds
We're going to do this to both of the pyruvates that came out of the glycolysis.
37 minutes 53 seconds
So if we cut this bond right here and we steal the two electrons and we give them to NAD plus, it will become NADH.
38 minutes 1 second
And we've managed to release this CO2 into the matrix.
38 minutes 8 seconds
It'll diffuse out of the mitochondria, out of our cell, into our bloodstream, out of our lungs.
38 minutes 13 seconds
We get rid of it as waste.
38 minutes 15 seconds
And then what we do is we take a placeholder to satisfy this poor carbon.
38 minutes 19 seconds
Because if we break this bond and steal the electrons between the red carbon and the black one, this black carbon does not have a fourth bond like it's supposed to.
38 minutes 27 seconds
So it's not going to be happy.
38 minutes 28 seconds
It's going to be reactive.
38 minutes 29 seconds
And so we go whoop and we put in a placeholder that's called Coenzyme A.
38 minutes 35 seconds
So coenzyme A is going to be this COA molecule attached to a sulf hydro group.
38 minutes 42 seconds
And by taking that hydrogen off, it's easy to attach the sulf hydro group to acetyl COA.
38 minutes 47 seconds
It's just a handle a placeholder to keep this carbon happy because now we've got to go.
38 minutes 53 seconds
I got to get rid of this one and I got to get rid of that one.
38 minutes 55 seconds
And then I've broken apart all the carbons that I started with initially.
38 minutes 58 seconds
So this very first step is going to convert A3 carbon pyruvate into two carbon acetyl COA, right?
39 minutes 6 seconds
It's an acetyl group here.
39 minutes 8 seconds
This carbonyl and methyl is an acetyl group attached to coenzyme A as a placeholder.
39 minutes 15 seconds
OK, so we've stolen a couple of electrons by breaking a bond and given them to NAD plus to make NADH.
39 minutes 22 seconds
And we've released a carbon atom.
39 minutes 23 seconds
So we're going to get 2 molecules of NADH from these two pyruvates and we're going to get 2 molecules of CO2 released from these two pyruvates.
39 minutes 30 seconds
OK, not too, not too difficult.
39 minutes 33 seconds
We're skimming, right?
39 minutes 34 seconds
We're skimming electrons off wherever we can as we're breaking this thing down.
39 minutes 39 seconds
And so acetyl COA is this molecule here, an acetyl group with a COA.
39 minutes 43 seconds
And the first thing that's going to happen is we're going to get rid of that COA.
39 minutes 46 seconds
It's just a placeholder, like a bookmark, OK.
39 minutes 49 seconds
And so this is giving you an example of what this looks like.
39 minutes 52 seconds
And COA is actually quite large coenzyme AI don't guess, I don't need to go into details about this, but you can see there's a bunch of phosphate residues in it.
40 minutes 1 second
It's looks like there's a purine base at the end of it.
40 minutes 5 seconds
But the part we want that we're going to use is this part right here, this acetyl group.
40 minutes 10 seconds
So it's got a methyl and a carbonyl and that's it.
40 minutes 14 seconds
This is just a placeholder that gets recycled and reused.
40 minutes 17 seconds
Throughout the cell, but it gets added on to this part.
40 minutes 21 seconds
OK.
40 minutes 22 seconds
All right.
40 minutes 23 seconds
So the third step of glucose oxidation, breaking down glucose molecules.
40 minutes 28 seconds
And I guess when I talk about it happening in three steps, the actual breaking apart of glucose happens in three steps, glycolysis, pyruvate oxidation, citric acid cycle.
40 minutes 39 seconds
The fourth major step is where all the business of making ATP happens.
40 minutes 43 seconds
But by then glucose is gone.
40 minutes 45 seconds
OK, Remember that after glycolysis, the majority of the energy is stored in pyruvate.
40 minutes 53 seconds
And then you start to see that there's some energy left in acetyl COA, but you're losing bits of it by breaking bonds and skimming off electrons.
41 minutes
And so acetyl COA is going to be fed into this pathway.
41 minutes 4 seconds
This the cycle called the citric acid cycle.
41 minutes 7 seconds
It's got a few names.
41 minutes 8 seconds
Sometimes it's called the TCA cycle, but citric acid is an intermediate molecule or intermediate metabolite that's in this cycle and one of the first that was probably identified, which is why it's called this.
41 minutes 19 seconds
And so the goal here is to take those two additional carbons and break them apart and get rid of them and then try to skim as many electrons as we can off of this cycle because we need them at the last step to be able to produce ATP.
41 minutes 33 seconds
Remember, electrons are energetic.
41 minutes 34 seconds
They'll do work.
41 minutes 35 seconds
If we pass them around from neighbor to neighbor, everybody does some work.
41 minutes 39 seconds
OK, So acetyl COA is going to end up being oxidized.
41 minutes 42 seconds
We're going to break the bonds here and steal their electrons and hand out these carbons as CO2 gas.
41 minutes 49 seconds
OK, so I'm going to take you stepwise through the citric acid cycle.
41 minutes 53 seconds
And I don't want you to get scared when you see the molecules.
41 minutes 56 seconds
I just want you to start watching as things move around as, as, as intermediate metabolites that are worked on at every step by enzymes, just like the other enzyme pathways, the metabolic pathways I showed you.
42 minutes 11 seconds
So the later when you see this, you're not like really scared by all the intermediates and the chemicals that you can look like it's a puzzle and see exactly where things move to understand what happened and how it got back to where you started.
42 minutes 24 seconds
Very similar to Calvin's cycle.
42 minutes 26 seconds
Part way through this, you're basically almost done.
42 minutes 28 seconds
Then you just have to recycle it all back to where you started.
42 minutes 31 seconds
If you don't, the cycle falls apart.
42 minutes 33 seconds
OK.
42 minutes 34 seconds
And so some of the potential energy that is released from acetyl COA is going to be used for these purposes.
42 minutes 40 seconds
We're going to break some more bonds and hand those electrons off to NAD plus who's our carrier?
42 minutes 45 seconds
And he's going to become reduced to to be NADH.
42 minutes 47 seconds
Remember, every NADH is hiding 2 electrons and got one extra proton and it's going to go deliver those electrons to the electron transport chain, hence the name.
42 minutes 58 seconds
And then we're also going to see his cousin FAD is going to be reduced also.
43 minutes 4 seconds
This is another electron carrier that gets made at the other end of the pathway.
43 minutes 8 seconds
It's carrying two electrons also, but it's already, it doesn't have a positive charge on it.
43 minutes 13 seconds
So if you give it two electrons, you got to give it two protons and it becomes a stable molecule called FADH, flavin adenine dinucleotide.
43 minutes 22 seconds
It's going to take its electrons to the electron train, transport train also, but it hands them off only to one special complex.
43 minutes 28 seconds
And I'll tell you about that in the next lecture.
43 minutes 31 seconds
And then one of the other little skimming activities we get off of here, I know the image shows ATP, but ultimately that gets converted into something called GTP or GTP happens 1st and gets converted into ATP.
43 minutes 44 seconds
Whatever you're, you're stealing phosphates back again to make an energetic molecule, right?
43 minutes 48 seconds
So there's a little bit of that.
43 minutes 50 seconds
And this isn't done intentionally to make ATP.
43 minutes 53 seconds
So we live.
43 minutes 54 seconds
This is because you're using a phosphate temporarily for a job and then handing it back off to ADP.
44 minutes
This is just, you know, for the sake of chemistry.
44 minutes 3 seconds
OK, All right, now we're going to walk stepwise through this.
44 minutes 5 seconds
Don't get scared.
44 minutes 6 seconds
It's not going to kill you.
44 minutes 7 seconds
But I want you to keep track of the colored carbon atoms.
44 minutes 11 seconds
The ones you come in with are not necessarily the same as the ones that get kicked out of this pathway.
44 minutes 18 seconds
OK.
44 minutes 19 seconds
So here we've got acetyl, COA acetyl, and the acetyl group is just a carbonyl and a methyl, right?
44 minutes 25 seconds
Chapter 3 and C 11 and O, and it's going to be attached to this COA coenzyme A.
44 minutes 32 seconds
The bulk of this is going to be added on to the first intermediate in the citric acid cycle that becomes like a holder or a carrier, and it's called oxaloacetate.
44 minutes 44 seconds
We're going to swap out the COA and there's an enzyme that does this.
44 minutes 48 seconds
I've taken away the enzymes so that it's not super confusing.
44 minutes 51 seconds
There's an enzyme that takes off the COA and adds the rest of this on to oxaloacetate.
44 minutes 57 seconds
And you can see by losing this double bond right here with oxygen and making it a single bond, giving oxygen a, a hydrogen atom, we can add on acetyl COA and this carbon is happy.
45 minutes 10 seconds
Everybody's happy.
45 minutes 11 seconds
They all have enough, all the carbons have enough bonds and now what you've created is 123456 carbon sugar.
45 minutes 20 seconds
You took a four carbon, you added two, and you created A6 carbon intermediate.
45 minutes 24 seconds
And citrate is actually used in many places as a source of energy and many metabolic pathways.
45 minutes 31 seconds
And so start paying attention to the colors.
45 minutes 33 seconds
Here are the red carbons that we added.
45 minutes 35 seconds
Here are the blue ones.
45 minutes 36 seconds
These are the ones that are going to end up going.
45 minutes 39 seconds
They're going to leave.
45 minutes 40 seconds
Notice why this is already set up as CO2 Break that bond and it's gone.
45 minutes 46 seconds
It goes away as gas.
45 minutes 47 seconds
Same thing with this one.
45 minutes 49 seconds
This is already set up as CO2 Cut that bond off and you release it as the CO2 molecule.
45 minutes 54 seconds
No problem.
45 minutes 55 seconds
And so in our first steps, we're just going to start rearranging things.
45 minutes 59 seconds
You're going to see that a lot of metabolic pathways of chemistry is you move here, you move there.
46 minutes 4 seconds
It's like a Rubik's Cube where you're trying to rearrange the colors of the shapes to get to the part you want.
46 minutes 9 seconds
And so by using water and then taking it back out again, we're literally just swapping a hydroxyl group from here to here.
46 minutes 17 seconds
And we've taken off one hydrogen from this carbon and given this one a hydrogen instead.
46 minutes 22 seconds
Do you see how you're kind of swapping?
46 minutes 24 seconds
We've converted it from citrate into ISO citrate.
46 minutes 26 seconds
OK, So we're just kind of swapping around.
46 minutes 29 seconds
All right, So follow the arrows and see what happens.
46 minutes 33 seconds
Now ISO citrate is going to get converted into something called alpha ketoglutarate.
46 minutes 38 seconds
And what's going to occur is we're going to break some bonds, OK?
46 minutes 43 seconds
So see how NAD is involved here.
46 minutes 45 seconds
We're going to steal some electrons and hand it off to NAD.
46 minutes 48 seconds
So it becomes NADH and we're going to release 1 carbon dioxide molecule.
46 minutes 55 seconds
Now let's count where it happens from.
46 minutes 57 seconds
So carbon, red carbon's the same.
46 minutes 59 seconds
Black carbon.
47 minutes
Look at this.
47 minutes 1 second
This one gets cut off and disappears.
47 minutes 4 seconds
We break this bond, we steal those two electrons and we hand them to NADH, to NAD Plus, and it becomes NADH.
47 minutes 11 seconds
And remember for every single sugar molecule, there's two of these acetyl coase going through the citric acid cycle.
47 minutes 17 seconds
So you're going to end up with two NADH.
47 minutes 20 seconds
And by cutting this off, it's already in the form of COO CO2 break this bond, now it's CO2 gas and it goes away.
47 minutes 28 seconds
And so that's the 1st place where we release this.
47 minutes 30 seconds
And now you've got A5 carbon intermediate called alpha ketoglutarate, OK?
47 minutes 36 seconds
And so the next thing that is going to be different here is you're also rearranging this hydrogen atom is gonna be taken off.
47 minutes 44 seconds
That's where this comes from.
47 minutes 46 seconds
And because you took it away and you're gonna take this one away, take two of them, This has to double bond with oxygen 'cause otherwise oxygen's not happy and carbon's not happy, which is why this now looks like it's double bonded.
47 minutes 58 seconds
OK, which do you think is the next CO2 that's gonna be cut off this molecule?
48 minutes 5 seconds
Probably the blue guy here at the bottom right.
48 minutes 7 seconds
He's lined up and ready to go.
48 minutes 9 seconds
If we break this bond, we steal the two electrons out of it, and we find a way to satisfy carbon.
48 minutes 14 seconds
We can release this as CO2 gas.
48 minutes 17 seconds
And that's exactly what's going to happen.
48 minutes 19 seconds
So this is gonna end up being cut off by an enzyme and released as CO2 gas, but now you have to satisfy this carbon.
48 minutes 29 seconds
So we're gonna steal the electrons that are in the bond, and we're gonna give it 1080 plus, OK, and we're going to make NADH with it.
48 minutes 39 seconds
But we have to swap in a placeholder because otherwise carbon is missing a fourth bond.
48 minutes 43 seconds
And COA Coenzyme A is a good placeholder.
48 minutes 46 seconds
It's clearly floating around in the matrix to be used.
48 minutes 49 seconds
So we're going to transfer Coenzyme A onto the end of this carbon, and now it's got four bonds and it's happy.
48 minutes 55 seconds
But we have managed to take its electrons, and we took this hydrogen atom right off of COA, and that's where that came from.
49 minutes 3 seconds
And so we're going to do this twice.
49 minutes 4 seconds
We're going to get 2 NADH produced here simply by swapping off this carbon and stealing the electrons that broke the bond and then going, OK, satisfy this guy by putting on a succinal A, a coenzyme.
49 minutes 17 seconds
And then we'll take the coenzyme back.
49 minutes 18 seconds
We'll swap it out with something else so that we can start converting it back to where it's supposed to be.
49 minutes 24 seconds
All right, the next step, so that converts alpha ketogliterate into succinyl COA.
49 minutes 30 seconds
And if we take off the COA, succinyl COA becomes just succinate.
49 minutes 33 seconds
OK, simple way of converting it to A4 carbon intermediate that's now making its way back to regenerating oxaloacetate.
49 minutes 42 seconds
Now this looks kind of messy, but what happens here in this process, in order to steal this COA back and convert this group down here from a carbonyl to a carboxyl, we need to have a ready oxygen to give this group.
49 minutes 59 seconds
And the easiest way to do that 'cause they're always floating around is use inorganic phosphate, which is just PO4 floating around in inside the matrix.
50 minutes 9 seconds
And so an enzyme is gonna swap off this COA and add on an inorganic phosphate that looks like this right here.
50 minutes 18 seconds
And so it's going to add one of these at the oxygen to this carbon.
50 minutes 21 seconds
And now it went from a carbonyl to a carboxyl.
50 minutes 26 seconds
What happened to do that is we added the phosphate and then took almost all of it back.
50 minutes 33 seconds
If you add on a phosphate PO4, OK, to the end of this, but then you take back PO3 and you add it on to an ADP, you can leave behind one oxygen atom.
50 minutes 45 seconds
And so you end up with COO.
50 minutes 46 seconds
And so that's all it's doing.
50 minutes 50 seconds
It's swapping out the succinyl COA.
50 minutes 52 seconds
Instead of adding to something plain like an H, it needs to convert back into COO because notice how many of those are in these molecules.
51 minutes 1 second
You're trying to get it back to the original COO that's present at the beginning of this pathway.
51 minutes 7 seconds
And so you've managed to convert this back.
51 minutes 9 seconds
So now you've got a carboxyl group, you've got like 2 carbons in the middle that are saturated and another carboxyl group.
51 minutes 16 seconds
So we're realigning our molecule to then rearrange it to back to oxaloacetate.
51 minutes 21 seconds
And so we steal back most of that phosphate and we make one molecule of ATP.
51 minutes 25 seconds
It's not because we're trying to produce energy at this step.
51 minutes 29 seconds
It's 'cause you used a phosphate as a placeholder, cut most of it back off and left an O behind and then regenerated ATP from it.
51 minutes 36 seconds
OK, Succinate is gonna be converted into fumarate, which is the next intermediate metabolite.
51 minutes 43 seconds
And what's gonna happen is we're gonna steal electrons by removing some HS.
51 minutes 50 seconds
Look what happens here.
51 minutes 52 seconds
This H right here is going to be taken off of this carbon, and it's going to be added on to FAD.
52 minutes 1 second
And this H right here, one of those is going to be taken off and added to FAD.
52 minutes 7 seconds
And so that makes them FAD H2.
52 minutes 10 seconds
And then look what happens in Fumarate.
52 minutes 13 seconds
He lost AH, and he lost an H.
52 minutes 16 seconds
So they had to double bond between each other in order to be satisfied.
52 minutes 19 seconds
Remember, carbon has to make 4 bonds always.
52 minutes 21 seconds
So if you steal one hydrogen from here and one hydrogen from here, these two have to double bond.
52 minutes 27 seconds
But you can now take those electrons and hand them off to your electron carrier and you have converted succinate into fumarate.
52 minutes 34 seconds
OK?
52 minutes 35 seconds
Now fumarate is going to be converted into malate.
52 minutes 38 seconds
We need to get rid of this double bond, and we're going to use water to help us do that.
52 minutes 42 seconds
OK, so look what happens.
52 minutes 44 seconds
We've got chapter and chapter.
52 minutes 46 seconds
We're going to use a water molecule and we're going to give the OH to the carbon on the top and the other H to the carbon on the bottom.
52 minutes 53 seconds
OK.
52 minutes 54 seconds
So that's all we're doing is we're making sure that they're happy and satisfied and that they don't have double bonds between the carbons.
53 minutes
It's OK.
53 minutes 1 second
We want to get back to just this double bond up here.
53 minutes 4 seconds
And so then malate is going to be converted into oxyloacetate.
53 minutes 8 seconds
And now we're back where we started.
53 minutes 10 seconds
And the way that that happens is we're going to use, we're going to, we're going to remove some electrons here and we're going to give them to NAD Plus.
53 minutes 21 seconds
All right, So what are we removing?
53 minutes 24 seconds
Well, we're going to sort of rearrange these.
53 minutes 26 seconds
This carbon on this side is going to end up this guy.
53 minutes 31 seconds
We're making the different shape, making it AT shape.
53 minutes 33 seconds
This carbon right here is going to be this guy in the middle.
53 minutes 37 seconds
And we're going to take away some of these hydrogens.
53 minutes 40 seconds
We're going to take both of these hydrogen atoms off and force this to double bond.
53 minutes 45 seconds
The Chapter 2 is the same and the carboxyl's the same.
53 minutes 48 seconds
And so we're stripping away these oxygens and we're handing them or these hydrogen atoms, I'm sorry, we're handing their electrons off to NAD.
53 minutes 55 seconds
Plus what's left is its protons.
53 minutes 56 seconds
And now we've got NADH and we're going to do get two of those.
53 minutes 59 seconds
So we've got two NADH, one CO2 released, the 2nd CO2 released, CO2's done, no more carbons left in the molecule.
54 minutes 7 seconds
And then we've got two more NADH.
54 minutes 10 seconds
We've got two ATP, two FADH, two, and two more NADH.
54 minutes 15 seconds
And so how many electrons is that total?
54 minutes 17 seconds
Well, if every NADH is carrying two, we've got 246810121416.
54 minutes 28 seconds
We got 16 electrons coming out of the citric acid cycle that will all be sent over to the electron transport chain to do the work of making ATP.
54 minutes 38 seconds
So this is a good pathway for scavenging electrons and sending them over like fuel to the electron transport chain.
54 minutes 46 seconds
All right.
54 minutes 47 seconds
And so this is a summary that takes away the actual structures of the molecules, but it does help you to look and see what bonds have changed.
54 minutes 54 seconds
And then as you look at other chemical processes and biochemical processes, they're not so scary if you just realize that each enzyme is making one minor change and you get to a point in the cycle where everything's got to go back to what you started with.
55 minutes 6 seconds
Otherwise the cycle won't continue.
55 minutes 8 seconds
And so citric acid cycle is the end step.
55 minutes 11 seconds
It completes the rest of glucose oxidation.
55 minutes 14 seconds
We went from six carbons to two threes.
55 minutes 16 seconds
We went from 2 threes to two twos, and then we went from 2 twos to none.
55 minutes 21 seconds
And we broke in all the bonds and still so in all the electrons we possibly can.
55 minutes 26 seconds
And so the energy that comes out of that oxidation of an acetyl COA molecule, just one of them, which is half a sugar, you get 3 NA, DH1F, Ed, H2, and one GTP, which ultimately is converted into ATP.
55 minutes 39 seconds
And so in total, from 1 sugar molecule, you're going to get 6 NADH.
55 minutes 43 seconds
Just from citric acid, you're going to get 2FA D, H2, and you're going to get 2 GTP.
55 minutes 50 seconds
And so those guys are really important.
55 minutes 52 seconds
The carriers, they're going to take those electrons that were stolen out of the bonds of sugar, and they're going to send them over to the electron transport chain where they're going to be used in a special process to produce ATP.
56 minutes 4 seconds
And you've managed to release your CO2 as waste.
56 minutes 9 seconds
OK, now we look at this and we go, well, that's a lot of business, whole lot of things happen, lots and lots of electrons, not a lot of ATP yet though, right?
56 minutes 18 seconds
So glucose oxidation really is the payout of it is just getting all the electrons.
56 minutes 25 seconds
You only get like a couple ATP molecules, nothing really crazy, right?
56 minutes 29 seconds
And so every single glucose molecule that's gonna be oxidized, it's gonna be oxidized down into 6 carbon dioxides.
56 minutes 37 seconds
OK, six carbons, 6 carbon dioxides are gonna be released, right?
56 minutes 41 seconds
You break 6 into two halves, you get 2 threes, 123456.
56 minutes 46 seconds
They're all gonna be released as carbon dioxide gas.
56 minutes 49 seconds
And so by reducing by by oxidizing the sugar, you end up taking those electrons and reducing NAD plus to NADH.
56 minutes 58 seconds
And so you end up reducing in total through the whole process, 10 molecules of NAD plus to 10 molecules of NADH.
57 minutes 5 seconds
Remember, all the HS are hiding, there's two electrons hiding in each of these.
57 minutes 8 seconds
So that's 20 electrons.
57 minutes 10 seconds
In NADH you get 2 molecules of FAD reduced to FAD H2, right?
57 minutes 16 seconds
And each one of these is holding two electrons.
57 minutes 18 seconds
So that's four more electrons.
57 minutes 20 seconds
OK, so that's 24 electrons, and then you're gonna get a total of 4 molecules of ATP.
57 minutes 26 seconds
So remember, you had an investment phase at the top where you invested 2, but then you got those two back, +2 more plus two more.
57 minutes 35 seconds
So really you're only totaling 4 molecules of ATP.
57 minutes 38 seconds
Now if you think 4 molecules of ATP is enough to keep you alive, you're sorely mistaken.
57 minutes 43 seconds
And so it's very clear that this is not where all the ATP is produced, that that must be the end payout.
57 minutes 50 seconds
Even Homer's kind of confused with all the ATP, but you did get all the energy in the form of the electrons you've harvested them.
57 minutes 57 seconds
OK, so this portion in white here is the glycolysis part.
58 minutes 1 second
The pyruvate processing is the little skinny part here.
58 minutes 3 seconds
And then the citric acid cycle is really where the electron payout is.
58 minutes 7 seconds
Look, NADHNADHNADHFAD, H2, NADH, that's where all the electrons are coming out in the citric acid cycle.
58 minutes 14 seconds
And so notice the interesting way this is graphed also, this is the free energy change relative to glucose, as glucose is oxidized as a function of the process of oxidizing it.
58 minutes 30 seconds
Sorry about that.
58 minutes 31 seconds
So here we've got free energy, right?
58 minutes 34 seconds
Remember that in an exergonic process like this, the delta G that's given off should be negative.
58 minutes 42 seconds
And notice that as you progress through the stages of glucose oxidation, that's what you get.
58 minutes 49 seconds
You're getting more and more negative free energy.
58 minutes 53 seconds
So there's a lot of free energy -700 kilocals per mole, a lot of free energy that's being released from this molecule.
59 minutes 2 seconds
The negative delta G is good.
59 minutes 4 seconds
That's an exergonic reaction, giving off energy that's gonna, in this case, we're harnessing that in the form of electrons to go do additional work for us as we oxidize glucose, right?
59 minutes 16 seconds
There's nothing left.
59 minutes 17 seconds
By the time we get all the way through the citric acid cycle, everything has been stripped out in the form of electrons.
59 minutes 22 seconds
And it's really fascinating to see what they're gonna do next.
59 minutes 25 seconds
And you're gonna see that the next time we talk.
59 minutes 28 seconds
Thank you so much for your attention.
59 minutes 29 seconds
I really do hope that cellular respiration doesn't scare you.
59 minutes 32 seconds
It's very challenging to learn the first time because you start to lose the understanding through the molecules, right?
59 minutes 38 seconds
You look at a lot of carbons and HS and oxygens, and it gets really confusing.
59 minutes 42 seconds
But if you just understand what's moving around where, and you'd ignore the enzymes for a little while until you know they need to be put back into the process.
59 minutes 51 seconds
But recognize the point of each step.
59 minutes 54 seconds
The breaking of glucose, making it unstable, trapping it in the cell first so it can't leave.
59 minutes 59 seconds
Making sure that the grading of glucose always looks low in the cell by converting it into something else and then unstabilizing it and breaking it apart.
1 hour 7 seconds
And chopping, chopping, chopping, stealing the electrons from the bonds, releasing CO2 as waste, and giving those electrons over to the carriers, the electron carriers who will transport them to the electron transport chain.
1 hour 19 seconds
So don't lose the forest through the trees.
1 hour 21 seconds
Don't focus too hard on the molecules.
1 hour 22 seconds
I'm not going to make you draw those.
1 hour 24 seconds
I just want you to understand what's happening in this process.
1 hour 27 seconds
This is a huge process that if anything causes it to cease, it can very quickly lead to death.
1 hour 35 seconds
And so it's very important to have a strong foundation in cellular respiration.
1 hour 38 seconds
After all, everything you do, every step you take, every electron you break, every bond you break is is done to support cellular respiration.
1 hour 49 seconds
All right, until next time, I hope you have a wonderful day and you'll be hearing from me again very soon.