Hi. It's Mr. Andersen and in
this podcast I'm going to talk about cellular respiration. Sometimes students confuse respiration,
breathing, just breathing in and cellular respiration and they are linked. Cellular
respiration however is going to take place at the level of a cell, more specifically
inside the mitochondria. And so we need oxygen for that. But it's basically taking our food
and then breaking it down in the presence of oxygen to make ATP out of it. What if you're
a bacteria? Can you do respiration. You sure can. You don't need a mitochondria to do respiration.
They can actually use their outer membranes to do aerobic respiration. And so basically
if you are a track athlete, so this is Usain Bolt right here, when you run you're using
respiration to make energy in the form of ATP that allow your muscles to move. And so
this is a quick little study I did. I took all of the world records currently right now,
from the 100 to the 10,000. And so this is Bekele is the guy who owns the 10,000 meter
record. And what I did is I figured out their pace. In other words how fast they're running,
this would be in meters per second for the 100, 200 all the way down to the 10,000 meter
run, which is a little over six miles. And what you can see in this graph is that the
pace is quickly going to drop off and then it's pretty much going to stabilize. And if
we were to go out to the marathon or continue, basically we're pretty effective at running
at a specific pace. But we die really quickly when we're sprinting. And so a way to think
about that is the two things we're going to talk about in this podcast is we're going
to talk about aerobic respiration. And so aerobic respiration is going to be respiration
in the presence of oxygen. But we also have almost like a turbo button that is anaerobic
respiration. And so if we really need to go fast we can get that extra speed that we have
up here by doing our anaerobic respiration. The problem if you've ever run is that when
you get out to this 400 meter you get a build up of lactic acid and it's incredibly painful
and so you can't keep that pace going. An example of a lab I did in class, and it's
weird how this exactly mirrors it. What we did was the muscle fatigue lab. So basically
you had a tennis ball and in one hand you had to squeeze it as many times as you could
in ten seconds. And then do another ten seconds, and do another ten seconds and this is the
class average. So the class average looks around 25 times in ten seconds. But you can
see that it quickly drops off and then it kind of levels off. And so the same thing.
This would be that aerobic respiration. And then this is going to be that anaerobic respiration.
And it was fun to see the students faces because as they start to go anaerobic their arm just
starts to build up the lactic acid on the inside of it. But before we get there let's
talk about respiration and what it's for. It's for heterotrophs. So we're heterotrophs
and basically what we're doing is we're taking organic compounds in the presence of oxygen
and we're converting that to carbon dioxide and water. What else are we generating? ATP.
Now what kind of things are doing this? Animals, fungi, bacteria are all heterotrophs and they're
using the organic material to actually make energy. Luckily we have autotrophs like plants
and algae. And basically what they're doing is they're converting that carbon dioxide
and water back into organic materials. The only thing that's a little deceptive is that
plants are also going to break down those organic compounds and so they do cellular
respiration as well. And so everything's doing cellular respiration. It's how we get energy
out of our food. Okay. Here's our equation. And again if you know what photosynthesis
is, this is simply the opposite. We're going to take glucose in the presence of oxygen,
so here's glucose and here's O2, and then we're going to break that into carbon dioxide,
water and then we're going to generate a little bit of ATP. Now where does the energy sit?
The energy sits right here in this hydrogen on the outside of that glucose and watch what
happens to that hydrogen. It's going to fall down and it's going to grab on to the oxygen
because oxygen wants electrons. And so that's where the energy is coming from. What the
energy's used to do is it's used to make ATP. And ATP is that little fuel that we use in
all of our cells. This slide is funny, but it's saying this, "Behold the power of oxygen".
So this fire comes from oxygen pulling electrons close to it. And so there's a huge amount
of energy found inside that pull of electrons towards oxygen. Now if we were to do this
inside our body we could get a lot of energy out of our food but we would also burst into
flames. And so we do it in a really controlled process. Just like when we learned photosynthesis
and we had to learn the parts of the chloroplast, when you're learning cellular respiration
you have to learn a few parts of the mitochondria. So first of all we have these folds on the
inside of the mitochondria. Those are called the cristae. And basically what we have is
two membranes. We're going to have an inner membrane right here and then we're going to
have an outer membrane right here. And then this space in the middle is called the intermembrane
space. And on the inside, mitochondria we think used to be bacteria of their own and
so they'll reproduce through binary fission. They have their own DNA. They have their ribosomes.
But they're kind of almost living inside us, not as a parasite but as a symbiant. They're
actually helping us as we generate energy. So there are three steps in cellular respiration.
Let's start with the first one. So the first one is going to be glycolysis. The second
one normally we think of as the Kreb Cycle. And then the third one is going to be the
electron transport chain. And so the first one, I love this diagram here because it's
putting glycolysis outside the mitochondria. And so this is going to take place outside
the mitochondria. Where would that be? Well that would be in the cytoplasm of the cell
inside your body or it would be right outside a bacteria. But what happens in glycolysis,
basically we're taking glucose, glucose is a six carbon molecule, and in glycolysis we're
going to break that down into two molecules of pyruvate. Each of those have three carbons
inside it. So the 2 three carbon molecule, that's what glycolysis does. What do we generate
in there? Well we generate a little bit of ATP. For one glucose molecule in glycolysis
we're going to make 2 ATP. The other thing that we make is a chemical called NADH. What
we're basically doing is we're transferring high energy electrons to NADH and we're adding
protons to it as well. And we'll get to NADH in just a little bit. Let's follow pyruvate
then. Pyruvate is going to diffuse into the mitochondria and then we're going to have
this pyruvate dehydrogenase complex. And basically what it's going to do is it's going to convert
that three carbon molecule into acetyl CoA. This is co-enzyme A. So basically now we have
a two carbon molecule that is going to go into the Kreb Cycle. Now since we're going
from a three carbon pyruvate to a two carbon acetyl CoA we're giving off carbon. And that
carbon is going to be given off in the form of carbon dioxide. And so when you breathe
out a third of that carbon coming out of you is going to come right here from this complex
inside the matrix we call this. I should have said that before. This is the matrix on the
inside of mitochondria. Okay, let's keep watching acetyl CoA. So it's a two carbon molecule,
where does it go next? It goes to the Kreb Cycle. And so in the Kreb Cycle we're going
to break it down further and we're going to get rid of these two carbons in acetyl CoA
and we're going to give those off as carbon dioxide. So we are getting rid of carbon dioxide.
What else are we producing in the Kreb Cycle? You can see here that we're producing a little
bit of ATP, 2 ATP, but we're also adding energy again to NADH and we're adding energy to,
its friend we'll call this, FADH2. And so what do NADH and FAHD2 have? They have these
high energy electrons. And they're going to carry those electrons to the third step which
is the electron transport chain. Okay. Let's get to the electron transport chain then.
And all of our energy pretty much that was in glucose is now in NADH and FADH2. So they're
going to transfer their electrons and those electrons are going to go through what's called
an electron transport chain. Basically they're moving through a series of proteins and the
energy of those proteins is used to pump protons. Protons are going to be hydrogen ions to the
outside of this inner membrane into what's called the intermembrane space. So now we've
built up all of these protons right here. What happens to the electron? The electron
is going to be added to other protons and oxygen that we breath in and that's going
to make our by-product which is going to be water. And so let's slow that just, slow that
for just a second, the oxygen that you breathe is moving in here and it's going to be that
last electron acceptor right in here in the matrix and we're going to take the protons,
what happened to those protons, they'll actually flow through a protein called ATP synthase.
Those protons will combine with the electrons and the oxygen and it's going to make water
which is going to be a by product of that. Now how much ATP do we make down here? Well,
we can make around 32 or 34 ATP in this last step. And so in the electron transport chain
we're making a whole heck of a lot of energy. And so it's worth taking a look at how that
actually works. So let's go to the electron transport chain. So to kind of situate ourselves
what do we have? Well we have NADH, our friends NADH and FADH2. What are NADH and FADH2 passing
off? Their electrons. Those electrons are going to move through the electron transport
chain like this. Every time they go through one of these proteins, it's going to pump
another proton ion out because that's the other thing NADH and FADH2 are bringing. They're
bringing these hydrogen ions. So we're going to pump these ions out here and pretty soon
what you get is a heck of a lot of positive charge out here in this innermembrane space.
There's no place for it to go. In other words, every NADH that we drop off, we're going to
move these electrons down and we're going to generate of whole heck of a lot of positive
charge in this innermembrane space. Now if you look right here FADH2 is actually dropping
it's electron a little bit farther down so it can't generate as much, but we're pushing
out either three protons or two protons depending on if it's NADH or FAHD2. Okay, what happens
to all of these protons out here? They can't go anywhere. They can't go outside the mitochondria,
they can't come inside the matrix, but they can move through this. This is called ATP
synthase. That's the name of this proton or protein right here. And basically this is
the site of ATP synthesis. And so basically as every proton flows through it, every proton
that comes through, we're going to generate ATP. And it almost works like a little rotor.
That every time a proton goes through, it switches it and it attaches that phosphate
onto ADP to make ATP. And that's why in the electron transport chain we can make all of
that ATP. There's nothing special about it. It's just that we're storing all of that energy
and instead of releasing it in a ball of fire, we're releasing it in little bits to make
a heck of a lot of ATP. Okay. So there's a problem. What happens if you don't have oxygen
pulling that electron the whole way? Well, let's say you don't have mitochondria present.
Well then you have a problem. The problem is this. It's okay to take glucose during
glycolysis and break it into two pyruvates because you're going to make a little bit
of ATP. But the problem is that you're adding those electrons to NADH. And so basically
what's happening is that we're adding electrons to NAD+ and we're transferring it to NADH
and so pretty much what happens is there's no more of this. And so glycolysis has to
shut down. Even though we can make a little bit of ATP with each breakdown of glucose,
eventually there's no NAD+ and so the whole process has to stop. And so nature of course
has a solution to this. And the first one is called lactic acid fermentation. This takes
place in your muscles. Especially when your muscles are under a huge amount of stress,
like if you're sprinting or if you're holding your breath for a long period of time. And
so basically what's going on, again there's no oxygen, there's no mitochondria, so let's
look what happens. Basically your cells are taking glucose in glycolysis and breaking
it down into two pyruvate molecules. So we were stuck here, remember with the NADH. But
then there's a further conversion. Basically what you're doing is you're converting the
pyruvate down into lactate or lactic acid. The nice thing about that is it's accepting
these electrons so we can make for of this NAD+ and then this can be recycled again.
And so basically what happens is that you can have this process occurring with glucose
over and over and over and over and over again. And every time you do that over and over and
over and over again, basically you're making 2 ATP each time. And so if you've ever done
sprinting, when you're sprinting you're getting aerobic respiration but you're also doing
anaerobic respiration on top of that. The problem with that is you're going to build
up lactate in your muscles and that lactate is like a toxin. You're going to have to break
it down and that takes oxygen. And so if you've ever watched a sprinter, especially somebody
who's run like the 400 meter dash, when they're done and they're interviewing them, they have
a hard time doing an interview because they have to keep breathing to take in more O2
and eventually get rid of that lactate. And so lactic acid fermentation is going to take
place in some bacteria and in muscle cells. But we have another solution to this in bacteria,
anaerobic problem of stopping right here with this full NADH and that's called alcoholic
fermentation. Alcoholic fermentation works the same way. Basically we break it down into
pyruvate. And then we break that further down into a chemical called ethyl alcohol or ethanol.
It's donating or it's accepting these electrons so it can recycle this NAD+ again. The only
difference here is that when we made lactate, that was a three carbon molecule. When we
do alcoholic fermentation what we're making is carbon dioxide and we're giving that off.
And so if you were to take yeast and put them in a bottle with a bunch of fruit juice, basically
what they'll do is they'll use up all of the oxygen then they'll switch to alcoholic fermentation.
What are they going to build up? They're going to build up ethyl alcohol. That's simply how
we make wine. And there's also going to build up carbon dioxide which we could let go or
for making beer, that's the carbonation that we're going to find in beer. And so again,
cellular respiration is just a quick way to get energy out of glucose. We use glucose
as an example, but we can do cellular respiration on pretty much any type of food. And it's
a way that we get energy. And we're doing it. Bacteria are doing it. Plants are doing
it. And I hope that's helpful.
