00:04
Cell respiration is a process of creating energy or atp from sugars.
00:13
So cell respiration can be of two types, aerobic or anaerobic.
00:18
And when we talk about aerobic respiration, the thing to keep in mind with aerobic is that it is with oxygen, whereas anaerobic respiration is without oxygen.
00:35
Now, when we talk about cellular respiration, we are going to focus on eukaryotic organisms.
00:45
And the reason we're going to do eukaryotic organisms is that in all eukaryotes, the majority of cell respiration occurs in the mitochondria.
01:06
Now, when we talk about cell respiration, it can be aerobic or anaerobic.
01:13
Aerobic is with oxygen.
01:15
Anorobic is without oxygen.
01:18
And what's going to happen is we're going to have the complete oxidation of glucose to carbon dioxide.
01:25
And when we do this, we're going to actually use a couple of coenzymes that act as electron transporters.
01:37
So let's kind of look at the whole process and look at where different parts are happening.
01:43
And then we'll look at the details of each step.
01:46
So cell respiration in general, we're going to start with glucose.
01:56
We're going to add oxygen, and we get out six carbon dioxide plus six molecules of water, and most importantly, energy in the form of atp.
02:21
And so again, we're going to have the complete oxidation of glucose to carbon dioxide.
02:29
When we say oxidation, we're looking at the transfer of electrons.
02:37
So glucose is going to lose electrons, and we're going to gain that energy from the electrons in atp.
02:45
So we're looking at energy transfer.
02:47
And in order to do some of this energy transfer, we need two co -enzymes.
02:54
And those two co -enzymes are f -a -d and n -a -d.
03:04
Both of these molecules are essentially electron transporters.
03:14
They readily accept electrons and can take them to other locations and give them to other electron -accepting molecules.
03:26
So i like to think of these guys as electron taxi cabs.
03:29
When they pick up those electrons, they become the high -energy molecules.
03:37
Molecules fadh2 and nadh.
03:43
And so these two molecules are very high energy.
03:47
And what gives them that high energy is that they're picking up electrons.
03:52
So again, when we look at cell respirations, a series of chemical reactions that are mediated by enzymes that allow us to transfer the stored energy and glucose to atp.
04:07
And we're going to look at one other thing before we're we kind of get started here, we're going to look at where things are happening.
04:17
So we know that the mitochondria is the site of cell respiration in eukaryotic organisms.
04:28
And when we look at the structure of our mitochondria, this is the matrix of the mitochondria.
04:36
This is our inner membrane, and that makes this the outer membrane, and this would be the inter membrane space, which makes everything outside of here the cytosol.
04:59
And so when we look at where reactions are happening, there's kind of basically four steps to cell respiration.
05:06
We have glycolysis.
05:11
We have the linking reaction or the intermediate step.
05:21
We have the krebs or citric acid cycle.
05:35
Let's get the word spelled right.
05:44
And then we have electron transport in chemoasmosis.
06:02
So when we look at each of these, glycolysis occurs in the cytosol.
06:16
Both the linking reaction and crabs are in the matrix.
06:22
And electron transport is on our inner membrane.
06:30
So now that we kind of know where things are happening, let's take a look at what happens in each step.
06:35
So we're going to start with glycolysis.
06:49
Move that up just a little bit.
06:50
There we go.
06:53
So again, as we already mentioned, it's happening in the cytosol.
07:08
When we look at the word glycolysis, lysis means to split.
07:13
So we are literally going to be splitting glucose, which is a six carbon molecule, to two, three carbon molecules.
07:35
Those two three carbon molecules are then going to be called pyruvate.
07:42
Now to get there, there's a series of steps that occur, and we're not going to look at all those steps, but instead we're going to look at what we need to get from glucose to pyruvate because we want to be able to look at what are the inputs and outputs of glycolysis.
07:59
So in order to do this, we have what's called the energy investment phase.
08:04
Dicholysis is energy investment, because we actually are going to put two atp in.
08:10
When we put our atp in, we get out to adp.
08:16
We're also going to use my high -energy electron transporters, n -a -d plus, and again, he comes out as a high -energy molecule, n -a -d -h, picking up electrons from glucose.
08:38
And then last, we're going to add for adp, to make for atp.
08:48
So from this we can kind of see that we're going to net to atp.
09:00
So for glycolysis, again, we're going to remember it happens in the cytosol.
09:10
And in glycolysis, what happens is we have glucose being oxidized to two pyruving.
09:23
We have two nadhs are added, or i'm sorry, two nad plus.
09:45
Again, those are our electron transporters, and they come out as two high energy nadh.
09:57
We invest to atp, and we get out to adp, we invest for adp, and again, get out to, or sorry, get out for atp.
10:25
And so then again, we have to make sure we note that our net is to atp.
10:33
Now this here becomes really important because when we look at this, we look at our inputs and our outputs.
10:46
We're going to use the products of glycolysis.
10:52
In other steps other than the atp.
10:56
We have just made two atp.
11:00
So right now, in terms of making energy, we have two atp.
11:11
I'm going to slide this over just a little bit.
11:18
So we're going to take our products, our 2 piruvate, and we need to transport them into the matrix of the mitochondria.
11:32
And we do that actively, active transport into the matrix of the mitochondria.
11:55
And we're ready to then further oxidize our pyruvate.
11:59
And like i said, i refer to this as the linking reaction.
12:11
And in this step, what we're going to do in, and again, it's in the matrix of the mitochondria, is we're going to convert pyruvate, which remember pyruvate is a three carbon molecule.
12:29
We're going to convert it to what's called an acetal, which is a two -carbon molecule.
12:45
Well, now you might be asking, where does that other carbon go? well, that other carbon, that third carbon, we make carbon dioxide.
13:05
So that third carbon gets released as carbon dioxide to the atmosphere.
13:10
Now, the conversion of pyruvate to the acetal, is done by an enzyme called pyruvate dehydrogenase.
13:20
So again, when we say enzyme -mediated reactions, we have an enzyme pyruvate dehydrogenase that's going to help convert pyruvate to that acetyl group.
13:39
Now, just like we have nadh or nad and fad plus are both coenzymes, to carry our acetyl group, we're going to combine it with coenzyme.
13:53
A.
13:55
So a lot of times you'll hear acetyl coa.
13:58
And we're going to use this in the next step.
14:02
Now as we convert our peruvate to acetyl coa, we are also going to make a little nadh.
14:15
So again, to do this conversion, we're going to add in nad plus.
14:29
And it comes out n -a -d -h.
14:34
So we kind of summarize this linking reaction.
14:40
What's happening here is that we have 2 piruvae, which are converted to 2, acetyl, and then again we have that co -a.
15:06
Now, co -a is not used up a neat reaction.
15:10
In fact, you'll see in the next step that it can be used over again.
15:15
It's just kind of helping to transport that acetyl into the next step of the reaction.
15:22
We're going to have, because there's two pyruvate, we have two acetyl, so two pyruvate from glycolysis.
15:30
Again, we're going to have two nad plus picking up those electrons and becoming high energy nadh.
15:46
Now, again, our perruvate, we're converted to decedalcote, but as part of that, i want to make note, remember, we're also going to create two carbon dioxide, and these go to the atmosphere.
16:03
So we are going to lose these as you breathe out.
16:22
So now we have the products of the glycolysis.
16:28
They went into the linking reaction.
16:32
We have the products of the linking reaction.
16:35
We're ready to go to the next step.
16:38
We're still staying in the matrix of the mitochondria.
16:42
Notice in the linking reaction, we did not make any atp.
16:47
So again, it's really important to note what are your inputs and what are your outputs.
16:52
So in the linking reaction, we did not make any atp.
16:56
What we did make is this high energy electron, transporter and our acetylcoa.
17:04
Now these nadhs from glycolysis, the nadh from leaking reaction, we're going to see them show back up again later.
17:14
So they're not being used yet.
17:18
We've made them, but we're not using them yet.
17:20
They'll show up again here in a minute.
17:22
All right, let's take this acetylcoa.
17:25
So we're ready to take this here and use it to in the next step.
17:49
So again, we're still in the matrix of the mitochondria.
18:03
So our acetylcoa is going to enter what's called the citric acid cycle or the crub cycle...