Hi. It's Mr. Andersen and in
this podcast I'm going to talk about bioenergetics.
Bioenergetics is basically how living systems
make use of free energy. And so this plant
right here is called arabidopsis. And basically
to the right of it is a diagram showing the
metabolism of just the Kreb's cycle in arabidopsis.
So basically this is how it's converting acetyl
CoA into carbon dioxide. And then making NADH
and FADH. And so this is incredibly complex.
Each of the red dots represents an enzyme.
And each of the lines represents chemicals
moving between those enzymes. And so you can
see that it's incredibly complex. But you
need to know the basics of bioenergetics.
And I could sum it down to this. Life requires
free energy. Or available energy. In other
words right now as you think your brain is
constantly cashing in ATP. And if you don't
do that, then you will die. So the opposite
of using free energy is death. And so basically
there are two laws of thermodynamics. First
law of thermodynamics you're probably familiar
with. It's basically the law of conservation
of energy. In other words energy is converted
from sun to wheat to plants to ATP to ADP,
using that energy in your brain. And so basically
the total amount of energy in a closed system
is going to be constant. In other words we
can neither create nor destroy energy at each
step. We're simply converting it. All energy
will eventually end up as a lowest form of
energy, which is heat. People are usually
not confused by that, but are sometimes confused
by the second law of thermodynamics. And basically
what that is is that as we move through time,
with each chemical reaction we're increasing
the entropy or the randomness of the universe.
In other words with each chemical reaction
from the sun to the ATP in your brain, we're
losing order. Or it's becoming disordered.
Now what seems to run counter that is the
idea of evolution. That evolution seems to
make things that are more and more complex
over time. And some people point to this as
a way that we're violating somehow the second
law of thermodynamics, which would be true
if evolution occurred over the whole universe.
But remember we're simply one part of the
universe. And so we can increase order is
one area by decreasing the order of the universe
around it. So that's basically the second
law of thermodynamics. Next we come to the
idea of Gibbs free energy. Some kids are confused
by Gibbs free energy. So we're going to step
through it kind of in a cartoon method for
talking about Gibbs free energy. This equation
is sometimes what confuses you. And so basically
the important thing to understand is what
happens with a change in Gibbs free energy.
Or change in free energy. And so we've got
three terms that we're going to kind of keep
track of. H stands for the total energy. T
stands for temperature. And S stand for entropy.
And so basically the first thing that you
should think about is that free energy, a
better was to think of that is available energy.
And so what we're going to do is go through
three spontaneous reactions. In other words
reactions that occur on their own. And we're
going to look at these values of H, T and
S. So let's start with the first one. This
is a ball at the top of a slide. Think about
this. Does it have more energy at the top
of the slide or at the bottom? And the right
answer is going to be at the top of the slide.
It's going to have more potential energy or
energy available to do work. And so let's
look at what happens to the H value. So the
H value is going to go down in a spontaneous
reaction. Let's go to the next example. Let's
say that we have a number of molecules that
are in a closed container. And think of these
as gas. And so the gas molecules are moving
around. And let's say I remove one of the
walls inside this container. Well, since they're
randomly moving around, they are going to
spread out covering that area. That's going
to increase the entropy or S is going up in
this case. We're becoming more and more random.
Let's say we remove the whole container, what's
going to happen? Well S is going to increase
as well. So again, in a spontaneous reaction
the amount of entropy is going to increase.
Now let's look at the last one. And let's
say that we have this bomb here. Is that spontaneously
going to explode? No. But let's say that we
increase the temperature. What's going to
happen then? Well now we're going to have
that spontaneous reaction. And so again this
is kind of a cartoon look at Gibbs free energy.
But let's kind of summarize what we've learned.
So in a spontaneous reaction, delta G is measured
in this case. So delta H, T and S. And so
looking back to the first one, in this spontaneous
reaction what happened to delta G? In this
case delta G actually went down. So delta
G went down. So what should that do to the
change in G? That should decrease it. Well
let's look at the next example, with the molecules
as they spread out. What happened to those?
Those ones increase. What else can increase
the spontaneous reaction? An increase in the
temperature. And so thinking mathematically,
if you increase these two values and were
subtracting it from the total energy, what's
going to happen to our delta G? Our delta
G is going to be negative. And so that's a
lot of stuff, but here's the summary. Basically
if we ever have delta G, and delta remember
change in free energy is less than zero, that's
a spontaneous reaction. If delta G is ever
positive that's going to be spontaneous in
the opposite direction. And so non-spontaneous.
Lots of times we refer to this as an exergonic
reaction. And this as an endergonic reaction.
And if delta G or the change in free energy
is zero, that means we're at equilibrium.
So we've talked a lot about what seems like
physics, but we haven't talked about biology.
So let's get to biology. Let's say we have
a molecule here of glucose in the presence
of oxygen, is that an exergonic or energy
releasing or endergonic, an energy taking
reaction? Well that's going to be an exergonic
reaction. It's releasing energy as we move
from glucose and oxygen to now carbon dioxide
and water. If we look down here at the delta
G, the delta G value is going to be negative
686 kilocals per mole. What does that mean?
If you take a mole of glucose you're going
to release that much energy. And so it's giving
off energy. So our change in G, or change
in free energy is negative. Where was that
energy? That energy is actually in the hydrogen
here. Because the hydrogen has a lot of potential
energy. And as it falls, watch the hydrogen,
it all grabs on to oxygen. So we're losing
that energy and we can release that energy.
Now let's look at an energy diagram. Well
basically that glucose and oxygen have a certain
amount of free energy over here on the side.
And when it's done they're going to have less
energy. And so if I were to draw the energy
diagram, it's basically going to go up and
then it's going to go down. So this is what
an exergonic or energy releasing reaction
looks like. Now if you know anything about
chemistry you know what this is up here. This
up here is called the energy of activation.
In other words you know that just sugar sitting
on your table doesn't spontaneously break
into water and carbon dioxide and giving off
you know fire. Basically you have to put a
little bit of energy into it to loosen those
bonds. And then it's spontaneously going to
breakdown. But if you look at that net. The
net change from delta G here, excuse me, G
or free energy here to free energy here, you
can see that there's a decrease in that. And
so the delta G is going to be less than zero.
That's in an exergonic reaction. If we look
at the next one. This is photosynthesis which,
even though chemically it's not the same exact
steps, it's doing the opposite. We're going
from carbon dioxide and water with energy
of light. And now we're making glucose. So
if you look down here at the delta G, now
it's a positive value. And so that's an endergonic
reaction. It requires energy. If we look at
the energy reaction or the diagram for that,
basically we have less energy than we do at
the end. And so what's happening? Well we
still have activation energy, but if we look
at the delta G it's going from a smaller value
to a greater value. And now we have a delta
G that's actually greater than zero. So this
is an endergonic reaction. So in a plant where
does this energy come from? This energy comes
from light. And so light is providing the
energy to actually boost it to a higher free
energy. Now why are plants doing that? Remember
they're doing that so they can do cellular
respiration. And then release all of that
energy in the form of ATP. They're not making
that sugar for us. They're making it so they
can have a storable amount of glucose. And
then they can break it down doing cellular
respiration and then produce energy in the
form of ATP. Speaking of which, this is ATP.
This is adenosine triphosphate. This last
phosphate remember can unattach. And so if
we do that, what's happened to our delta G?
It's negative. You can see that it's a lot
less than it was with cellular respiration,
and that's because it's a smaller molecule.
If we go back to ATP from ADP, that's going
to be a positive delta G. If we break the
phosphate, negative. If we form the phosphate,
that's going to be positive. And so constantly
inside my body as I move my muscles, I'm breaking
that ATP down to ADP to provide energy. And
then I'm making it again through cellular
respiration. And so what's important when
we're talking about bioenergetics? Well there
are two big chemical processes that are super
important. First one is photosynthesis. This
occurs in the autotrophs or the photoautotrophs.
Basically what they're doing is taking the
energy of light and then they're using that
to make glucose. And then secondly they're
taking that glucose, through glycolysis, Kreb
cycle and electron transport chain and then
releasing that in the form of ATP. And in
the next two podcasts I'm going to talk specifically
about photosynthesis and how that occurs.
And then cellular respiration and how that
occurs. But remember, the reactants of one
are the products of the other and vice versa.
And so the delta G is going to be the same.
Negative in cellular respiration. Positive
in photosynthesis. And I hope that's helpful.
