Cellular Respiration


Uploaded by bozemanbiology on 04.04.2012

Transcript:



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.