We begin our lecture on a bioenergetics which
is the final part of this course. We will
be speaking on certain aspects of energy of
systems and mostly later on the metabolism
of carbohydrates. If we consider the bioenergetics
of life, we consider the thermodynamics of
energy conversions in living systems.
We have seen before how we look at ATP as
the source of energy and it will be more apparent
now when we see how this energy of the breakage
of the high energy phosphate bond is actually
going to give us a lot of the energy that
is required to drive these processes. We have
the free energy from ATP and other high energy
compounds then the free energy from electron
transfer from one molecule to another in ordinary
oxidation reduction reactions where again
we will be using some compounds that we have
considered that have been derived from the
vitamins. Then we will be looking at some
metabolic pathways and involved in that we
will be looking mostly at the break down of
glucose, how glucose is broken down in the
body and in that there will be certain not
very many but some organic reaction mechanisms
and there will be some studies based on how
the energy is utilized in the processes in
glycolysis or the tri carboxylic acid cycle
where we have the final breakdown of glucose.
When we consider bio chemical energetics usually
the energy is actually harnessed by a process
that is called oxidative phosphorylation this
is an aerobic process. An aerobic processes
means it is a processes that requires oxygen.
This oxidative phosphorylation is the process
by which ATP is formed. And you realize that
since ATP is the currency of energy we require
its formation at a very high level as well
because its breakdown is going to finally
drive a lot of other processes that are going
on.
Therefore the formation of ATP is extremely
important and oxidative phosphorylation is
the process in which it is formed as electrons
are transferred from NADH or FADH2 to oxygen
by a series of electron carriers. Now we won’t
go into the details of all the mechanism but
we will just look at the broad overview of
how this oxidative phosphorylation system
works and how actually ATP is formed. Now
this process of oxidative phosphorylation
occurs in the mitochondrial membrane? You
have all heard or studied from your school
days that mitochondria is the power house
and what we look at it now is a bit more detailed
that the fact that it is the power house is
because it gets you the source of energy that
is ATP. In its mitochondrial membrane if we
look at the structure of mitochondria we have
this mitochondria system. This is, you know,
a picture of mitochondria and what we have
here is, we have the membrane, a charge across
this membrane and in here if you remember
these folds are called crystane.
These folds actually there is this inter-membrane
space and there is the inter-cellular space,
the cytoplasmic space the inter membrane space
and the outside of the membrane. These are
the three features we are going to consider
in the charge gradient across the membrane
and we will see how important that is in driving
what is called a proton pump. Because this
proton pump is essential for the formation
of ATP which occurs in the inner mitochondrial
membrane. But before we get into that we will
just lo at the basic aspects of energy in
equilibrium and how they are related in other
terms like delta G and all that. This is something
you have studied before.
But in general when we consider any energetics
or any equilibrium we look at a delta G factor
and we know that at equilibrium this value
is 0. We have here certain products and certain
reactants A + B going to C + D at a definite
temperature and associated with that we can
get a specific equilibrium constant and with
the equilibrium constant we know that when
we have the negative for the delta G0 prime
we are going to have a spontaneous reaction.
Now the prime usually if not mentioned otherwise
it refers to a biological system where the
temperature is -30 0C.
It is not your normal delta G0 where the temperature
is 25 degree C. If not mentioned the delta
G0 prime T has to be 37 degree C. If we look
at the variations if we just consider you
can see how different the variations get.
now the calculation here have been done at
25 degree C for the delta G0 prime but in
the normal cases when the temperature is not
mentioned it means you use 37 degree C for
your calculations. If we consider just one
mole concentration of reactants and products
what you will see here is how the order of
the equilibrium constant changes more than
a 100 fold for a relatively smaller value
of the kJ mol-1 changes. You have to be very
careful about this, this is due to the ln
feature that you have here. Since it is an
exponential dependence what you have is even
if you have just a 12 kJ mol-1 difference
here you are looking at a hundred fold difference
in your equilibrium constant which means your
reaction is going to get to equilibrium at
a much different rate than obviously if you
had just your energy at this power. When you
consider the values here you understand that
you are going to have a forward spontaneous
reaction, this is at equilibrium and this
goes in the backward direction a non spontaneous
reaction. Now when we consider the energetics
bio energetics requires energy coupling.
You do not have a continuous spontaneous reaction
usually because that is going to form a large
amount of products. You might not need all
those products all the time. so the whole
process of the formation of the products from
the breakdown of the reactants in the enzymatic
processes has to be tightly regulated. because
remember we studied feedback inhibition. What
was feedback inhibition? It was where you
had your final product inhibit the initial
enzyme. so what you are doing here in this
case is you have a spontaneous reaction that
drives a non spontaneous reaction. The energy
is coupled in such a way that the free energy
changes obvious reactions are additive. and
what we have is these enzyme catalyzed reactions
they are interpreted as two coupled half reactions
where you have the energy of one compensate
the energy of the other more than compensate
it where you are going to get a value that
is going to be making the specific reaction
spontaneous in nature. What happens is at
the enzyme active site the coupled reactions
are kinetically facilitated which means they
go at a specific rate but the individual half
reactions are prevented. You do not have just
a certain half reaction go on but when the
enzyme active site has both the reactants.
There is a coupled reaction that goes on and
the free energy changes of the half reactions
are summed to yield the free energy of the
coupled reaction which usually gets to a spontaneous
reaction a negative value.
I have an example. Essentially what we are
looking at? We are looking at a standard free
energy change. If we have a half reaction
that goes from A to B and another half reaction
goes from B to C then we can have the overall
reaction go from A to C and the standard free
energies of both of these are going to be
additive. It may so happen that you not have
the B component present in both cases, this
is one such case and the other case may be
you have a completely different reaction that
is actually going to provide the energy for
this reaction to go forward. That would be
a normal biochemical couple reaction and in
most cases we get the energy from the ATP
breakdown.
So what are we speaking about? We are speaking
about this high energy bonds of ATP. This
is a structure that you now recognize. And
what we have here is a very large - of hydrolysis
meaning that this breakdown is extremely spontaneous
in nature. Now the basis of high energy of
hydrolysis of ATP is due to the resonance
stabilization of products that you get. It
is also due to the electrostatic repulsion
between the negatively charged oxygen atoms
in ATP. Where are these negatively charged
oxygen atoms? They are here. You would not
have them one beside the other all the time.
So it would be relatively easier for it to
break of to give you ADP + Pi or AMP + PPi.
Also we have a high salvation energy of the
products which amongst to the high energy
of hydrolysis for ATP. The reactions that
require the breakdown of ATP are such reactions
that are going to have a + by themselves.
If we look at such an example the enzyme hexokinase,
a kinase is a transferace enzyme that transfers
a phosphate group. It is a transferace but
a kinase is a specific type of transferace
that transfers the phosphate group. Now, in
the reaction catalyzed by the process Glycolysis
the first step in the glucose breakdown is
the formation of glucose 6 phosphate, this
we will be studying in detail when we go to
the glucose breakdown. The formation of glucose
6 phosphate from glucose + Pi is a +14 kJ
mol-1 so by itself it is non spontaneous.
so you will not have your glucose with the
help of the enzyme hexokinase. This name hexo
means it is working on a 6 membered carbon
ring or your 6 membered glucose carbon sugar
here. It is a hexose, it is the kinase working
on the hexose so it is a hexokinase which
means that it is going to be involved in the
transfer of the phosphate ion from just the
Pi in this case two glucose giving you glucose
6 phosphate.
As I just mentioned this overall reaction
has a + . However, if you couple it with the
hydrolysis of ATP, ATP hydrolysis gives you
ADP + Pi and we have a very large negative
value here for the breakdown of ATP and when
you couple these two reactions together what
is happening is you have ATP + glucose form
ADP + glucose 6 phosphate giving you an overall
favorable of the reaction. This makes this
reaction spontaneous. So this is what you
would call energy coupling.
The structure of the enzyme active site from
which H2O is excluded prevents individual
hydrolytic reactions but it does favor the
coupled reaction. You understand that the
enzyme active sites are extremely specific
in the way they work. You have seen certain
enzyme active sites and how they actually
work. We will not go into the details of how
hexokinase works but for understanding the
energetics what you have to realize here is
that the non spontaneous reactions are couples
with other reactions that are spontaneous
in nature in the case ATP hydrolysis but this
together will give you a favorable energy
which makes the reaction go forward.
Nature has chosen certain specific hydrolysis
reactions for the specific types of non spontaneous
reactions. For example, in this case we need
ATP hydrolysis. but in some cases if the energy
is enough to be compensated by another specific
hydrolysis or another electron carrier or
whatever then it may not require this amount
of energy for the coupled reaction and then
what is chosen, another hydrolysis is chosen
to couple it so that we do not have too much
extra energy.
We can have this also. This is another case
where we have two separate reactions that
occur in the same cellular compartment one
is spontaneous and the other is not that would
be typical of a couple reaction and it is
coupled by a common intermediate. For example,
if we look at a hypothetical example that
involves PPi we have A + ATP going to B +
AMP + PPi. This particular reaction that occurs
in enzyme 1 has a + . It having a + means
it is non spontaneous. If we want to form
B from A we have to have a corresponding compensatory
reaction that is going to have a delta G that
is negative then we can couple it with this
reaction to give an overall spontaneous reaction.
And the energy has to be such that the negative
value obviously has to be more than this in
magnitude.
So, if we look at enzyme two that is breaking
up the PPi into 2 Pi it gives us a delta G0
prime of – 33 kilo joules per mole which
more than compensates for the spontaneity
of this one. So the overall spontaneous reaction
is going to give us A + ATP, B + AMP + 2 Pi.
Again we are looking actually at ATP breakdown.
We are not going to ADP + Pi in this case.
The first reaction itself is forming ATP is
breaking down into AMP + PPi. The reaction
which couples or which actually provides the
energy for the first reaction to go forward
is the PPi breaking down into 2Pi. So what
happens is this pyrophosphate is often the
product of a reaction that needs a driving
force and we have this break down. If you
look at both the examples that I showed you
both of them are breaking down ATP which means
that ATP has to be produced somewhere. If
you don’t have enough production of ATP
obviously none of these reactions are going
to be possible.
Therefore we are going to look at generally
how ATP is formed in a very simplistic manner.
We have looked at these molecules before.
We will go into some of the details of what
we looked at before. We considered these when
we studied vitamins and coenzymes. NAD+ is
a coenzyme that reversibly binds to enzymes
that is what is a coenzyme. FAD is a prosthetic
group that remains tightly bound at the active
site of an enzyme. We will see how these are
utilized basically in the process of oxidative
phosphorylation to actually give you in the
production of ATP. And these Flavin, we will
look at what these molecules are, the Flavin
nucleotides are tightly bound to what are
called flavoproteins. The proteins that have
the FAD or the Flavin nucleotides are called
flavoproteins and these are required in the
reactions of oxidative phosphorylation to
give you the energetics or whatever is required
for the production of ATP.
This is something we studied before where
we are looking at vitamin B3 (Niacin) where
we have cofactor forms that were NAD and NADP.
They are not tightly held, they are the cofactors
and reused reaction after reaction. We don’t
use them in the raw form here. We have to
transform them either to NAD+ or NADP. What
happens in these reactions is we have an oxidized
form and a reduced form.
What are these forms? When we are looking
at nicotinamide adenine dinucleotide we know
that we have the nicotinamide adenine dinucleotide.
A nucleotide has a single phosphate. A dinucleotide
has these 2 phosphates so we have a nicotinamide,
adenine and a dinucleotide so we have NAD.
It is an electron acceptor. The rest of the
molecule is not going to be required, this
is NAD+ this nitrogen has a plus (+) this
particular nitrogen has a +ve charge to it.
The only difference that we have between NAD
and NAD+ is this OH on the adenine nucleotide
is phosphorylated so we have NAD+ here, and
this is NADP+ here, we have the OH here and
this NADP+ with the phosphate here.
Now therefore the features of NAD plus or
the NAD plus are that we have the nicotinamide
that has been derived from niacin so this
is derived form the vitamin B3 (Niacin). It
accepts two electrons and one proton that
means a hydride and goes to the reduced state
NADH. Similarly, we have NADP+ and NADPH.
It is similar as I said it only has this extra
phosphate at the position. So the variations
that you are looking at are NAD+ and NADH.
If we look at the previous slide, the rest
of this molecule is required for recognition
for the enzymatic process but for the NAD+
going to NADH it is only this part that is
the nicotinamide part that is required so
we refer to rest of this whole portion as
nothing else but R. that is exactly what we
have. R is the rest of the NAD+.
We have the N+ here now what it does accept
is two electrons and a proton. This becomes,
it loses its plus and it has an additional
H so it is now NADH without the positive charge.
So what it accepts is two electrons and a
proton. The electron transfer reaction can
be summarized as NAD+ + 2e– + H+ ? NADH.
It is also written as NAD+ + 2e– + 2H+ ? NADH
+ H+. You have to recognize here that the
reactions that NAD+ or for example when I
show you FMN and FAD as well these reactions
are going to occur in or these co-factors
or prosthetics groups are going to be required
in enzymatic reactions that are going to be
of what type of a redox type. Because either
the hydrogen has to be taken away or the hydrogen
has to be supplied so in that case we cannot
have the ATP come into the picture. So, when
it is a certain dehydrogenase enzyme or an
oxidized type of enzyme it will require NAD+
or FMN or FAD for the particular reaction
to go forward. So you have to recognize in
the energetic procedure what sort of transformation
is taking place. because each of these are
transformation steps breakdown steps that
we are going to study and as we go through
them we will see that obviously when you want
to add a phosphate with the help of a kinase
that is going to transfer the phosphate you
cannot use any of these you have to use ATP.
but when we have a redox reaction that is
going to use your redox reaction that is the
dehydrogenase or an oxidize you will require
NADP+ and NADH and depending on the enzyme
that you have you will either use this or
you will use FMN or FAD.
So basically what we have is this is one example
where we have ethyl alcohol going to acetaldehyde
where we are looking at NAD+ ? NADH + H+.
Basically what happens is the oxidation involves
removing 2 protons and 2 electrons from the
substrate NAD+ so what is your substrate?
The substrate is going to the products where
you are removing 2 protons and 2 electrons
from the substrate and that is going to NAD+
to form NADH. NAD+ is taking up these 2 protons
and 2 electrons. It accepts a hydride ion
that is the equivalent of 2 electrons and
a proton, it adds this to the nicotinamide
ring and the additional proton is released
to water. So basically any reaction that is
going to require the removal of 2 protons
is going to use NAD+. NAD+ is going to take
up those 2 protons, that is simple as how
it actually works.
The other one that we are going to be using
in oxidative phosphorylation for FAD or FMN
is derived from this vitamin riboflavin vitamin
B2 and the structure there is a Flavin mononucleotide
where what we have is, we basically have this
isoalloxazine ring.
This ring isoalloxazine ring alloxazine ring
is what is required here and what is going
to be taking up the hydrogen. So again when
we are looking at it we have this is Flavin
mono nucleotide until this part, why mono
nucleotide because we are talking of one phosphate.
When we have Flavin adenine dinucleotide we
have the adenine here and the other phosphate
here. We have FMN or FAD.
But each of these we are going to refer to
this entire portion as R. Now then depending
on the energetics of the process depending
on what is utilized or whether it is FMN attached
to the enzyme or FAD attached to the enzyme
the reaction will proceed accordingly. But
basically what is going to happen is this
ring is going to take up the hydrogen. How
is it going to do that? We have a reduced
substance, we have FAD.
Therefore the H2 from the reduced substance
is taken up by the FAD similar to NAD+ going
to NADH so we have FAD going to FADH2. This
is an example of where we have cytochrome
electron system in the electron transport
chain. So we have the reduced substance going
to an oxidized substance with the help of
enzyme a dehydrogenase in this case that is
going to abstract the hydrogens from the substance
from your reactant and give it to FAD forming
FADH2. What happens is this is the rest of
the ring you now recognize,e this is just
the top portion that we are interested in
so we have FAD, the hydrogens are taken up
by this nitrogen and this nitrogen.Therefore
we have one here and one up there. So we have
the hydrogen addition in two steps finally
getting from FAD to FADH2.
So what happens is, we have R group here,
FAD and what is going to happen? We have the
2 protons taken up by the 2 nitrogens on FAD
and it is going to give you FADH2 so we have
FAD + 2 e– + H+ ? FADH2. Where it is getting
these protons from? It is getting them from
the certain substrate that has to be converted
to the product which will not have the 2 hydrogens.
This is an example where we have succinate.
Succinate dehydrogenase what is it going to
do is abstract the 2 hydrogens. In the abstraction
somebody has to take it up it is as simple
as that. What is going to take it up? FAD
in this case is taking it up and what is happening
to FAD? It is forming FADH2. So this is also
reaction. So succinate dehydrogenase alone
will not work. First of all it has to have
a place to put these two hydrogens. FAD takes
up the 2 hydrogens forming FADH2 and in the
event you get your fumarate from succinate.
We also have FMN going to FMNH2.
You are having a release of your NH3. Basically
the reactions are going to have proton transfers,
electron transfers in your changes. Now in
these systems we looked at some examples where
we have NAD+ going to NADH, FAD going to FADH2
or FMN going to FMNH2. Now what is happening
in these electron transfer systems, all of
you know Nernst equation? When we consider
the biological systems the electrons are transferred
from one molecule to another just in a normal
electron transfer reaction. But these can
occur actually in four different ways in biological
systems. What are the different ways? We can
have direct electron transfer that is one
possibility. We can have them transferred
as hydrogen atoms that contain a proton and
an electron. This is a common mechanism for
oxidation of carbon compounds that we just
saw using enzymes called dehydrogenases. We
can have hydride transfer the hydride transfer
we saw in the process of NAD where it takes
up the hydride so the NAD+ goes to NADH.
Therefore we can have direct electron and
we can have transfer as hydrogen atoms. We
can have hydride transfer or we can have direct
reaction with oxygen. Usually in aerobic systems
where you have oxygen available you can have
direct reaction with oxygen as occurs in certain
oxygenase reaction. These are the four processes
by which we can have electron transfer. All
of these are redox processes and all of these
will be using redox enzymes. Redox enzymes
are either dehydrogenases or oxidases. so
we can have just direct electron transfer,
we can have hydrogen as hydrogen atoms that
contain a proton and a electron. We can have
hydride transfer or we can have a direct reaction
with oxygen in the presence of oxidases.
The enzymes we are looking at are dehydrogenases
and oxygenases. When we go to the breakdown
or the whole metabolism of carbon hydrates
as soon as you look at the reactant and the
product you should first of all be able to
identify what is going on. If it is loosing
hydrogens you are having a redox reaction
taking place, and in the process of a redox
reaction is taking place the enzyme therefore
will be using is either a dehydrogenase or
some sort of oxidase a reverse process that
is going to happen then and in that case you
have a cofactor that is going to be NAD+ or
the prosthetic group FMN or FAD.
When you look at these reactions you have
to recognize the type of enzyme that is involved,
whether the reaction is of redox type or a
transferase type, whether the reaction is
in isomerization where the enzyme will be
nothing but an isomerase. When we study the
different processes of metabolism of the carbohydrates
you should be able to recognize how each of
these enzymes require a specific cofactor
or a specific prosthetic group for it to work.
In the energy coupling in ion transport we
have say the transfer of S1 S2. In utilizing
the breakdown of ATP to form ADP + Pi we have
a couple reactions. So we are coupling this
usually to a certain chemical reaction when
we require the energy we are using hydrolysis.
We are using the hydrolysis of ATP, why is
it so efficient? It is because of the resonance
stabilization and certain other factors that
I mentioned so the hydrolysis of ATP in the
couple reaction is going to give us the possibility
of ion transport. But we also have to remember
that we have to produce ATP. Now you recognized
this as a membrane and we have a certain enzyme
that is going to act as a proton pump.
As you see this picture what happens here
is this is your mitochondria the outer surface
of the mitochondria so this is also a membrane
so we have a lipid bilayer here we also have
an inner membrane that has these folds. This
is the cross section of your mitochondria.
This is also a lipid bilayer. 
These folds are called cristae. Therefore
this is the outside of the mitochondria. This
is the outer membrane of the mitochondria
and this is the inter membrane space. This
is the inner membrane of the mitochondria.
So this is the inner membrane, this is the
outer membrane and this is the inter membrane
space; it is not outside the mitochondria.
It is within the mitochondria but outside
the intra cellular space of the mitochondria
rather called the internal matrix. So it is
away from this matrix but also away from the
outside of the cell. It is this area, this
is the place the inter membrane or rather
the inner membrane where the process of oxidative
phosphorylation occurs.
For the production of ATP we need H+. ATP
reactions occur in the mitochondria, the reactions
that we just mentioned the couple reactions
occur in the mitochondria so the ATP has to
be present in the matrix of the mitochondria
for the reaction to occur. What happens therefore
is this H+ is required for the production
of ATP. Now if we go back to the slides here
we have what is called a positive side that
is called the P side and we have a negative
side called the N side.
Let me just go to the next slide this one,
here we have the matrix side that is the N
side so in my diagram this is the N side the
matrix, this is the P side that is the positive
side. so what I am going to do now is I am
going to blow up a part of this region so
what you have to understand is we have the
whole mitochondria here, we have the inner
folds of the inner membrane that are called
Cristae of the mitochondria (CRISTAE), we
have an inter membrane space that is the P
space and N space which is the matrix.
When we look at therefore a single fold so
this becomes a single Cristae and we have
our outer membrane. This is my matrix and
this is my inter membrane space. What happens
here is here I have a positive charge which
means I have a larger number of protons here
and outside or rather in the matrix I have
what is called the N side. It is very difficult
to sort of mention an inside and outside here
because all of this is actually inside but
this is inter membrane and this is matrix
side. We have a relatively less part or the
N side is more negative.
For the production of ATP or first of all
we have to realize that we need ATP inside
the matrix. The ATP production has to be inside.
But for the ATP production we need protons.
The protons are on at a higher concentration
in the inter membrane space. So what you have
to do is we have a certain protein that is
called ATP synthase for which we will look
at the structure in a moment, where we have
the protons that have to get in here and ATP
is produced here.
The ATP has to be produced in the matrix because
all the reactions are going on in the matrix
but it requires a large amount of protons
for it to occur. That means what has to happen
is protons have to be pumped from the inside
to the outside against a proton gradient because
there is a positive charge on the outside
and a negative charge on the inside. But since
we require the protons for the ATP to be produced
protons have to be pumped to the inter membrane
space, that is what we have here. Therefore
we have a P side and an N side. The N side
is the negative, where is this N side? It
is the matrix of the mitochondria and where
is this P side? It is the inter membrane space
of the mitochondria.
This is where a higher concentration of protons
exists but we require an even more amount
of protons for ATP to be produced. Hence what
you have to do is protons have to be pumped
from this to that side. That is essentially
what is happening. Now, because of this negative
and positive side here you have a membrane
potential developed.
When an ion is 
transported from negative to positive which
is the membrane potential is positive. Because
you are going from a negative value to a positive
value what is ? It is a positive value. Now,
when you have the matrix side the N side that
has a low proton or low hydrogen ion concentration
a low proton concentration a negative electrical
potential. The inter membrane side which is
the C2 concentration in this case has a high
proton concentration and has positive electrical
potential. So when you are looking at the
values you have a RT ln what is your product
in this case? It is going to the inter membrane
side so it is C2/C1. You have a Z F which
is nothing but your NFE it is the potential.
Now, when you consider the low H+ concentration
and the high H+ concentration you can link
the logarithm of the hydrogen ion concentration
with the pH. So if we just work this out I
have my i.e. . Where is 
my C2? My C1 is low H+ and my C2 is high H+
and you have to remember that the high H+
is in the inter membrane space and you are
still pumping in H+ to that space because
you have to make ATP. This is plus your ZF
.
Now if you want to convert we know that the
pH = -log[H+]. So all we have to do is relate
this with the pH. So we can write this 2.303RT
other part. Now what we have here is, it is
going to be where is going to be equal to
then the pHN going to pHP side i.e. . Now
where is this low H +? it is on the N side
and where is the high pH? The high H+ is on
the high H+ means low pH so we have this relation.
This is your .
So basically what you are doing is you are
using this relation based on the delta pH,
what is this delta pH? It is the difference
of the hydrogen ion concentrations between
the matrix and the inter membrane space. This
is the membrane potential, what membrane potential?
it is the inner membrane potential. Therefore
we have the energy associated with the proton
gradient. Now, when we look at the energy
available from electron transfer it is conserved
as a proton gradient and what happens is when
we have this reaction of NADH going to NAD+
you recognize that if NAD+ is going to form
NADH there has to be a reaction that is going
to get it back to NAD+ so it can be reutilized
just like you would have your enzymes.
So similarly as we are breaking down the ATP
we have to produce ATP and we will we will
look at the production of ATP also. So there
are certain reactions for example this reaction
that will more than compensate for the amount
of the that you need for this proton pump.
You see what a very large amount of energy
this is -220 kJ mol-1 and this energy will
be utilized for your proton pump to maintain
the proton gradient. Why do we have to do
that is because we have this proton pump,
we have the H+ to produce the ATP that is
why we require this. So this is what is the
proton pump. We have our specific requirement
where the protons have to be pumped from the
negative side to the positive side for the
production of ATP.
So we have basically the picture of the mitochondria
here. This is the outer membrane and both
of these are liquid bilayers. We have an outer
membrane, we have an inner membrane and within
the inter membrane space is high H+ ion concentration.
We have a low H+ here the hydrogen H+ is pumped
from the lower H+ concentration to the high
H+ concentration because excuse me ATPase
there is a protein called F1 F0 F1 ATPase,
ATPsynthase that does nothing but synthesize
ATP.
And this proton gradient drives protein reactions
on the inner membrane which allows them back
into the center of the mitochondria which
uses this to generate ATP from ADP. Essentially
what you want to do is you want to produce
ATP which is why you are pumping all the protons
into the inter membrane space for the production
of ATP. This ADP the purpose of this oxidative
phosphorylation is to use the energy to make
ATP that is accomplished in two steps.
First we have the proton gradient then we
have a transfer of electrons through a series
of systems. We are not going into the details
of the systems but this is the essential reaction
that takes place where n is about three so
it means that we have to pump in three protons
for the production of one ATP. So three protons
have to go from where, we have to get the
ATP, we have to go from ADP + Pi + n H + P
that is the positive end to ATP + H2O in the
negative. Therefore in the matrix side the
ATP is produced. Why is it produced there?
It is because all the reactions that are taking
place do not happen in the inter membrane
space and all of the enzymatic reactions occur
in the matrix space.Actually I will just show
you this.
This is where we have the inter membrane space
where we have a large number of positive.
We have a protein that is called the ATP sythase
the details of which we will do in the next
class where we are looking at a series of
reactions that are actually going to get us
into the formation of ATP. What we learnt
today was how we can actually derive from
vitamins specific cofactors and coenzymes
that are going to result in coupled reactions.
We have ATP, the hydrolysis of ATP is going
to give us enough energy to couple with another
non spontaneous reaction to give us a spontaneous
reaction like the example I showed you the
hexokinase where we are going from glucose
to glucose six phosphates and we are getting
the phosphate from the breakdown of the ATP.
In the dehydrogenase or oxidase reaction we
are using NAD+ or FMN or FAD that are going
to be coupled with enzymes such as dehydrogenases
or oxidases because the compounds have to
lose their hydrogens and these are going to
be utilized or in the redox reaction they
are going to be taken up so either you have
to have a reduction or an oxidation and based
on what reaction you have the enzyme is going
to have as a cofactor either NAD+ or FAD.
What we will see in the next class is how
this ATP is actually formed and we will then
go on to the metabolism of carbohydrates.
Thank you.
We continue our discussion on biochemical
energetics. What we learnt last time was that
we need the process of oxidative phosphorylation
to create ATP. Now we are going to see how
that process actually works in the inner mitochondrial
membrane. Basically what we have in an aerobic
process or an oxygen requiring process is
this energy is harnessed by this oxidative
phosphorylation.
Now, what happens in oxidative phosphorylation
is the formation of ATP. Ultimately there
is going to be an electron transfer system
that is actually comprised of a number of
electronic systems, they are termed as different
complexes. We have complex 1, complex 2, complex
3 and complex 4. Each of these complexes are
highlighted by a set of proteins and apart
from the proteins there are special cofactors
and prosthetic groups that are extremely essential
for the process to occur. Now what we are
going to see is how this complex actually
helps in the transfer of the protons from
the inside that is the matrix side to the
intermembrane space and then we will see the
action of what is called ATP synthase in the
production of ATP.
So what we are going to look at is the oxidative
phosphorylation which is the process by which
the ATP is formed as the electrons are transferred
from NADH or FADH2 to oxygen by a series of
electron carriers. This actually occurs in
the inner mitochondrial membrane.
We looked at this picture last time where
we found out that even though there is a high
proton concentration in the intermembrane
space we still need to pump protons from the
inside that is a matrix side to the intermembrane
space so that ATPase which we will see later
can actually produce the ATP that is required
for the functioning of all things in the body.
So the purpose of this oxidative phosphorylation
is to use the energy to make ATP. The way
this is accomplished is in two steps: First
the energy is conserved as a proton gradient
across the inner mitochondrial membrane………plus
we have, associated with the h plus, what?
The electrons.So we have to have systems that
are going to allow or take up these electrons
and then provide a balance in the whole system
of events.
Now this is what we have in our system. This
is the outer mitochondrial membrane. I am
going to go at this a bit slowly. The circles
that you see there, what are those circles?
Those are the polar head groups of the lipid
bi-layer. This is the inner mitochondrial
membrane. Now, in the inner mitochondrial
membrane…. So here we have our polar head
groups. So, dangling here we would have the
lipid bi-layers. These are the lipid chains
and similarly here also we have our fatty
acid chains hanging from a polar head group.
Now, what we have here, here, what is this
space? This is our intermembrane space. Here
is the matrix of the mitochondria, the matrix
of the mitochondria. Now, what you have in
this matrix is, remember, here what do you
have? We have a high h plus concentration.
Inside here we have a low h plus concentration.
What are we doing? We have to pump h plus
to the other side, why? To make ATP. This
is the system, the pore, remember, I mentioned
the pore in the inner mitochondrial membrane
that this is eventually going to provide the
h plus or transfer the h plus into this matrix
so that we can produce ATP. Now we are going
to look at this system in a bit detail.What
we have is, we have here certain complexes.
Now each of these complexes is you can see
is what, it’s kind of an integral membrane
protein.
