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Oxidative Phosphorylation II
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
- Intro 0:00
- Complex III 0:19
- Complex III Overview
- Complex III: Step 1
- Complex III: Step 2
- Complex IV 8:42
- Complex IV: Cytochrome Oxidase
- Oxidative Phosphorylation, cont'd 17:18
- Oxidative Phosphorylation: Summary
- Equation 1
- How Exergonic is the Reaction?
- Potential Energy Represented by Transported H⁺
- Free Energy Change for the Production of an Electrochemical Gradient Via an Ion Pump
- Free Energy Change in Active Mitochondria
Biochemistry Online Course
Transcription: Oxidative Phosphorylation II
Hello and welcome back to Educator.com, and welcome back to Biochemistry.0000
Today, we are going to continue our discussion of oxidative phosphorylation.0004
In the previous lesson, we looked at complex 1, complex 2; we gave a little bit of an overview of what was going on.0008
Now, we are going to move on to the rest of the electron transport chain beginning with complex 3.0014
OK, complex 3, let's see what we have here.0020
Now, we have all of these high-energy electrons that are collected by the molecule ubiquinone, and now, it is in the form of ubiquinol, its reduced form.0033
Now, it is going to pass on its electrons.0042
It is going to pass its electrons to cytochrome c, and here is how it is going to be.0048
Let's go ahead and give a name to this.0055
This is called cytochrome bc1 complex.0059
It is also called its formal name Q:citochrome c oxidoreductase.0069
This is the name of the complex; normally, we just call it the cytochrome bc1 complex.0087
That is the common name; the formal name, when you see this :Q to cytochrome, that means something is being transferred from Q to cytochrome c, and it is an oxidoreductase.0092
Oxidoreductase, you remember from the classification, it involves the transfer of electrons.0103
OK, in the complex 3, in this particular case, electron transfer, it takes place in 2 steps.0110
It is really an unusual complex.0122
OK, the first step, what you have is a molecule of QH2.0130
Now, it has its electrons; what it does, it releases its hydrogen ions into the inter-membrane space.0136
Again, this is part of the proton pump quality of complex 3.0145
It releases the 2 Hs into here.0150
Well, one of its electrons, it gives it over to ultimately cytochrome c, and we will talk about the actual sequence in a second; but it goes from Q to cytochrome c.0155
The other electron, now, what it does is it gives it over to another molecule of just plain old Q, and what ends up happening is this Q ends up turning into the QH radical that we talked about earlier.0166
Now, another molecule of QH2 diffuses through the bilayer.0182
It release its 2 hydrogen ions into solution.0187
Now, we have a total of 4 hydrogen ions being passed into the inter-membrane space.0192
It, again, gives 1 electron to Q.0198
It passes it to cytochrome c; it gives its other electron over to this radical, and this radical, now, ends up becoming QH2.0204
In the second step, 1 molecule of QH2 is used up.0212
1 molecule of QH2 is created; there is no net gain or loss of QH2.0218
Ultimately, it is only this 1 molecule of QH2 that ends up passing its electrons- 1 here to cytochrome c, the other here, another 1 to cytochrome c, the other here.0225
We have actually passed 2 electrons, and we have pumped 4 protons into the matrix.0235
That is what is happening here; complex 3, well, it is definitely not altogether that easy to follow.0242
There is a lot going on with complex 3; let's talk about what happens here.0249
Electron transfer takes place in 2 steps.0253
The first step, a molecule of QH2 - the reduced form of ubiquinone, which is called ubiquinol - releases 2 hydrogen ions to the inter-membrane space.0257
OK, that is the P side- the positive side.0279
Now, 1 electron passes as follows.0284
This is the inner workings of the complex: QH2 to an iron sulfur protein to cytochrome c1 and ultimately to cytochrome c.0292
This is the actual path of the electron, and 1 electron passes as follows: QH2 to cytochrome b to Q, which, now, becomes QH radical.0307
OK, the first electron passes from QH2; this QH2 and this QH2, they are the same.0347
One electron, it goes from an iron sulfur protein to cytochrome c1 to cytochrome c.0354
It is, now, here; the other electron passes to a cytochrome b and then, to Q, which, now, becomes QH- this Q radical.0360
That is what that becomes; now, for step 2, another QH2 molecule, it does the same thing.0371
It does the exact same thing; it does the same thing.0390
It releases 2 hydrogen ions into the inter-membrane space.0400
Well, 1 of the electrons passes as QH2, iron sulfur protein, cytochrome c1 to cytochrome c, and the second electron, it passes as QH2 - this is the same QH2, 1 electron goes 1 way, 1 electron goes the other way - to cytochrome b; but now, it goes to the radical, which, now, becomes our QH2 again.0410
In step 2, 1 QH2 is used, and 1 is created.0468
So, there is no net gain or loss.0490
OK, and like complex 1, complex 3 is a proton pump, hydrogen ion pump- that is it.0494
That is all that is going on there; OK, now, let's take a look and move on to complex no. 4.0520
OK, this is complex 4.0529
The movement is now from cytochrome c.0537
The electrons are going to finally make their way to O2- the final destination of these electrons.0541
The name of this is cytochrome oxidase.0547
OK, let's talk a little bit about...I want to say something about the oxidase.0556
An oxidase is a general class of enzymes that catalyze oxidations, where O2 is the electron acceptor, but O, itself, oxygen atoms, do not appear in the product.0565
Both atoms of oxygen end up being reduced to water.0622
One atom takes 2 electrons and 2 hydrogens to become 1 molecule of water.0626
The other oxygen atom takes another 2 electrons and another 2 hydrogen ions to become water.0630
Oxygen, itself, does not show up anywhere; it is pure oxidation up here in the product.0637
OK, now, let's see what actually goes on here.0645
In this particular case, this is also going to, sort of, happen in 2 steps.0654
What you see here, though, is the final result.0659
Now, you have this cytochrome c; all of the electrons have been passed to cytochrome c.0665
Cytochrome c is like a ubiquinone in a sense that it is a mobile electron carrier.0670
Again, complex 3, complex 4, we need to get the electrons from here to here.0678
Cytochrome c is what moves on the lipid bilayer, through the lipid bilayer.0682
And again, it is just another molecule that carries electrons.0690
It carries/has 2 electrons, moves over here, gives up 2 electrons, moves back, takes 2 electrons, just back and forth- that is it.0694
It does the same thing; it just an electron shuttle is what it is.0700
The net effect is the following; 4 cytochrome cs pass their electrons to, this time, a copper-copper center, passes it on to a heme group, passes the electron to another heme group, passes the electron actually to a heme copper center, and now, these electrons, here is where O2 comes in.0705
O2 + 4 hydrogen ions plus these 4 electrons is reduced to 2 molecules of water.0730
In the process, also 4 hydrogen ions is pumped from the matrix into the inter-membrane space.0737
This is the net effect of what complex 4 does.0744
Cytochrome c passes its electrons ultimately to O2, reduces both atoms of oxygen in the O2 molecule to water.0748
OK, that is very, very important- 4 protons, 4 electrons, 2 each to form waters.0758
Now, we will go ahead and do a breakdown of the individual process.0766
Again, an oxidase is a general class of enzymes that catalyze oxidations where O2 is the electron acceptor, but O atoms do not appear in the product.0770
OK, now, this is different from the mixed-function oxidase that we saw earlier for the phenylalanine hydroxylase reaction.0779
Remember the first reaction of the catabolism for phenylalanine?0788
That enzyme, the phenylalanine hydroxylase, is also called a monooxygenase because it uses O2 as the electron acceptor, but one of the oxygens actually ends up in the product.0794
The phenylalanine becomes tyrosine; the other oxygen atom ends up being reduced to water.0808
In this case, an oxidase, both atoms end up getting reduced to water.0814
That is the difference; even though we call this an oxidase, that other one...you remember, we called it a mixed-function oxidase?0820
That is a really unfortunate, sort of, common name for it- mixed-function oxidase.0828
You will often hear it called a mixed-function oxidase.0831
Really, it is more proper to refer to it as a monooxygenase.0837
This is strictly an oxidase; I know, enzyme names, it is enough to make you want to pull your hair out.0841
Sorry about that; OK, now, let's go ahead and talk about this.0847
Let's see; the first step, we have 2 cytochrome c molecules.0857
Two electrons are passed to this copper-copper center, and then, these electrons are passed to something called heme A.0858
These electrons are passed to something called heme a3.0867
Actually, I am going to draw it a little bit this way.0870
I am going to go to heme a3CuB.0874
It is a heme copper center, and from here, the electrons are passed to O2.0903
However, the O2, it actually becomes O22-.0912
It is not fully reduced yet; now, 2 more cytochrome cs deliver 2 more electrons, and with 4 hydrogen ions taken up from solution, taken up from the matrix, this O22- now, it becomes 2 molecules of water.0920
OK, the 2 electrons that are passed from the 2 cytochrome cs only produces O22-.0968
Two other electrons from 2 other cytochrome cs pass through the same process, and now, the O22- is converted to 2 molecules of water.0974
And, of course, along the way - again, complex 4 is a proton pump - 2 H+s are transported into the inter-membrane space.0986
We had 4 protons from complex 1 being transported, 4 protons from complex 3 being transported, and now, 2 protons from complex 4 being transported.1010
This is all from the transfer of 2 electrons from NADH from the beginning of the electron transport chain.1019
For every 2 electrons that make it through the electron transport chain, 10 hydrogen ions are transported across the membrane.1025
That is a lot; that is a lot.1033
OK, now, let's see what it is that we have got here.1037
We have done complex 1, complex 2; now, let's go ahead and do a quick little summary, so that we know where it is that we stand.1042
NADH goes ahead and delivers its electrons to complex 1, and these electrons are passed to ubiquinone.1051
Four protons are pumped into the inter-membrane space.1059
Let's do this in...that is OK; let's go ahead and do this in black.1065
We have 4 hydrogen ions there; the succinate passes its electrons through FAD, again, to ubiquinone.1070
Complex 2 is not a proton pump; complex 3, the ubiquinone passes its electrons through complex 3 to cytochrome c, and in the process, we have pumped in, again, 4 hydrogen ions from the matrix to the inter-membrane space.1080
Cytochrome c passes its electrons through complex 4.1098
The electron transport chain, it reduces a molecule of O2 to 2 molecules of water.1102
Here, they show the stoichiometry is 1/2, but that is not a problem; and in the process, we end up transferring 2 hydrogen ions.1109
Now, we have 4, 4, 2; we have 10 hydrogen ions in the inter-membrane space.1119
This is the positive side; this is the negative side.1124
These protons, they want very badly to go over here both for concentration reasons and for potential reasons.1128
There is a build-up of charge, and there is a concentration gradient.1134
These protons fly through this molecule called ATP synthase.1138
Downhill, that extra energy is used to actually produce the ATP from adenosine diphosphate and inorganic phosphate.1143
Let's take a look exactly what is going on here, so equation 1.1154
Let's see if we can quantify this a little bit.1159
We have NADH + H+ + 1/2 O2 goes to NAD+ + H2O.1163
There is our H2O; there is our H2O.1175
This is per mole of NADH; per mole of NADH, we produce 1mol of water.1179
Perhaps it is better written if you like, if you do not like this 1/2, it is up to you because it might be better written as 2 NADH.1186
Each NADH deliver 2 electrons; 2 NADH, we have delivered 4 electrons.1202
We have pumped 20 hydrogen ions; we are going to end up producing this many waters.1207
2 NADH + 2 H+ + O2 produces 2 NAD+ + 2 H2O.1212
OK, I guess the question is: "how exergonic is this reaction?".1227
This flow of electrons, again, we said that it is exergonic.1237
It is this giving up of energy, that energy is what is used to actually produce the proton gradient that ends up ultimately falling back down.1240
That energy is used to fall back down; that is where that energy is used to produce the ATP.1252
Well, we want to see how exergonic this reaction is, the transfer of electrons.1258
How exergonic is this reaction?1264
Well, we know that ΔG is equal to -N x F x that, right?1272
The free energy of a particular process when there is a potential difference is the number of electrons transferred times the Faraday constant times the actual potential difference.1283
Well, let's see what this is; let's do a little bit of a calculation here.1296
Let's rewrite the equation: ΔG is equals to -N x F x that.1300
Well, we know what N is; we are talking about the transfer of 2 electrons.1310
We know what the Faraday constant is; it is 96,485J/V.mol.1315
OK, now, the...that is OK.1326
I will do it here; the potential for the NAD+ NADH, oxidation-reduction pair is -0.320V, and the potential for the O2 to H2O pair, that equals 0.816V.1332
The net, the reaction, this minus that, this minus that, this minus the minus that, it is 0.816 + the 0.320 gives me a total of 1.14V.1359
That is the potential difference here and the transfer of these electrons across the electron transport chain.1374
1.14V- that is huge, absolutely huge.1380
Now, let's go ahead and put this together; our ΔG, the amount of free energy that we are actually releasing that is available for other work is going to be -2 x 96,485J/V.mol x 1.14V.1384
And now, what I am going to do is I am going to multiply this; because this is per mole, we wrote our equation as 2 NADH.1411
I am just going to go ahead and multiply this by 2 because I want to do it for 2 moles.1418
When you end up doing this, you end up getting -440kJ.1425
2mol of NADH ends up producing, ends up releasing 440kJ of free energy.1435
This free energy is what is used to transfer the protons from the matrix to the inter-membrane space.1446
Now, this free energy is what is used to pump hydrogen ion out of the matrix.1454
Again, this 440kJ, this is what is coming from just those 4 moles of electrons traveling through the electron transport chain, from complex 1 all the way to complex 4.1480
In the process, in reaching oxygen, they actually released 440kJ of energy that can be used for something else.1498
This free energy is what is used to pump the hydrogen ions out of the matrix and into the inter-membrane space against both a concentration and an electrical gradient.1508
In other words, you have this membrane, and here, you have the matrix; and here, you have the inter-membrane space.1540
Well, you are trying to separate, you are trying to take all of this hydrogen ion and bring them all to this side.1553
You are trying to create; you are doing something that is unnatural.1562
It is not going to happen spontaneously; therefore, you need energy to actually do this.1566
You need to put in energy to run a process that is not going to happen naturally.1570
Naturally, the system wants to be at equilibrium; what you are doing is you are taking all these hydrogen ions, and you are pumping them, and you are putting them on 1 side of a barrier.1577
Now, you have a whole bunch of positive charge, a whole bunch of negative charge.1585
Not only have you separated charge, but you have also separated species.1589
Now, you have hydrogen ion here, no hydrogen ion here.1593
There is a concentration gradient, and there is an electrical gradient; you need energy to support that to make sure that it all stays on this side.1597
You are creating a bunch of potential energy, and now, when we open the floodgate of ATP synthase, all of that potential energy is going to release and create ATP.1605
All of this energy is used to do this, to run an unnatural process, to create this gradient, and as you create the gradient, you are making it actually harder and harder to pump protons.1614
As you separate the charge, as you move the concentration of hydrogen ion from 1 side to the next, you are making it harder for more of it to happen.1626
That is where this energy is going; OK, now, let's see what we have got.1635
Let me see; OK, now, the potential energy represented by these transported hydrogen ions, which are, now, ready to fall back down their gradient, is 2-fold.1645
You have the chemical part; that is the concentration difference.1698
That is the concentration of hydrogen ion on 1 side, virtually no concentration of hydrogen ion on the other side, and it is also electrical.1706
It is a separation of charge; you are creating a positive charge on one side of the membrane and negative charge on the other.1718
This is a lot of potential energy here; OK, now, we have an equation.1725
The free energy change for the production of an electrochemical gradient like this when you actually do this, when you pump an ion from one side of a membrane to the other side of the membrane, we have an expression for actually the free energy that is available from this.1736
The free energy change for the production of an electrochemical gradient via an ion pump is the following.1760
ΔG is equal to RT times the natural logarithm of c1 / c2 + Z, faraday constant, delta phi.1785
Let's talk about what some of this is; now, c1 and c2, they represent the concentrations of the ions on either side of the membrane.1798
c2 represent the concentrations of the hydrogen ion in the 2 compartments, and c1 is greater than c2.1809
In other words, we need this thing to be greater than 1.1835
c1, the concentration 1, that is the concentration of hydrogen ion in the inter-membrane space.1838
Concentration 2 is the concentration of hydrogen ion in the mitochondrial matrix.1844
OK, Z is the absolute value of the charge of the ion, which in this case is just +1.1851
It is just +1 in this case.1873
Hydrogen ion...well, yes, delta phi, now, delta phi is the transmembrane potential difference in volts.1877
In other words, once we actually have that separation of charge, a whole bunch of hydrogen ion, a whole bunch of positive, a whole bunch of negative, there is a potential difference.1900
We can measure that potential difference, and in this particular case, we actually have all of these numbers.1907
In active mitochondria, as it turns out - well, we are not going to worry about what the potential difference is, let's just move on to... - once we actually put the numbers in, this ΔG is approximately equal to about 20kJ/mol of hydrogen ion.1915
Well, since 2 electrons transfer 10 hydrogen ions, they pump - OK - 10 x 20.1950
This is about 200kJ/mol of NADH.1967
Well, since we decided to use the stoichiometry of 2 NADH, this is about 400kJ.1974
With 2mol of NADH, in other words, with 4 electrons transferred, with 20 hydrogen ions pumped across the membrane, ΔG approximately equals about 400kJ.1984
We said that the electrons, in moving through the electron transport chain, they release about 440kJ of energy per 2mol of NADH.2008
We have taken that energy, and we have preserved it.2024
Instead of just letting it dissipate as heat, we have used about 400kJ of that energy to actually produce this proton gradient.2028
Now that that proton gradient has...now this is potential energy, there is this 400kJ of energy that once these protons, once we open up the ATPase of molecule, these protons are going to want to fall back down their gradient.2038
They want to get to the other side from the inner membrane space.2053
Here is the membrane; they want to get to the matrix.2057
There is all of this 400kJ of energy that we have used from the 440 to pump to protons, but now that they are there, we have created this gradient.2061
Now, they want to fall back down; now, this 400kJ is actually potential energy, which can be converted into work.2070
This work is what produces the ATP; it is what builds the ATP from the ADP and the inorganic phosphate.2078
Of the 440kJ from the electron transport chain, about 400kJ is preserved as the proton gradient, and this is ready to be unleashed in the synthesis of adenosine triphosphate; and that is all that is happening- that is it.2089
This is a complete discussion of oxidative phosphorylation.2142
Once again, high-energy electrons, as they pass through the electron transport chain, they give up all of that energy.2146
The body uses that energy to pump protons and to create a proton gradient.2152
Now that that proton gradient is created, it has taken that energy, and now, it is potential energy.2158
Now, when protons fall back down their gradient going back into the matrix from the inter-membrane space, we are going to use that 400kJ to actually create ATP molecules that are going to be pumped out.2164
The body is going to use them however they see fit- that is it.2177
That is oxidative phosphorylation; thank you so much for joining us here at Educator.com.2181
We will see you next time, bye-bye.2185
3 answers
Wed Jan 17, 2018 3:32 AM
Post by Maryam Fayyazi on January 5 at 05:56:10 AM
thanks for incredible lecture. I was wondering if you cover cell Biology as well?
2 answers
Last reply by: Sally Reina
Tue Sep 5, 2017 1:51 AM
Post by Sally Reina on August 29, 2017
Hi Professor Raffi Hovasapian,
For Complex IV, it pumps out 2H+, but I am confused by the figure because it showing 4H+ being pumped into the intermembrane space. Can you explain this please?
Thanks!
Sally
1 answer
Fri Apr 7, 2017 6:52 PM
Post by Nikhat Siddiqi on March 25, 2017
Can you please give me a lecture on "Transport across biomembranes: free energy content of transmembrane concentration gradients for uncharged and charged solutes mathematical relationship"
Thanks
0 answers
Post by Phil Beauchamp on July 11, 2014
What about charge balance? 2 electrons total -2 in charge move from a NADH through the electron transport chain but they are moving +10 to the IM? Also, when the electrons move, they seem to usually move as hydride, moving a proton with them (or picking up one after a single electron transfer) yet the hydrogen seems like it is considered as H+. It is a little confusing.
0 answers
Post by Professor Hovasapian on September 10, 2013
Hi Vinit,
The answer is thermodynamics. The oxidation of 1 mol of NADH to NAD+ has 220 kJoules of Free energy. Some of this energy is lost simply by the inherent inefficiency of the proton pump. However, most of it ( about 200 joules is used to pump out those protons. This 200 kjoules is used to pump 10 moles of protons. So 1 molecule of NADH oxidized allows 10 H+ protons.
So the number 10 just happens to reflect the Total Free Energy available to do work, and the fraction of that which actually does the work of pumping out protons.
Hope that helps.
Raffi
1 answer
Tue Sep 10, 2013 8:18 PM
Post by Vinit Shanbhag on September 9, 2013
Thanks for the answer. Another question I had was, why only 10 electrons are pumped out per NADH molecule, I know that 4 protons make 1ATP by the ATP synthase, so 10 will make 2.5. Thanks.
0 answers
Post by Vinit Shanbhag on September 7, 2013
Hi, forgot to mention that your lectures r really helpful. Thanks a lot.
1 answer
Sun Sep 8, 2013 4:26 AM
Post by Vinit Shanbhag on September 7, 2013
difference between atp synthase and atpase?
does krebs cycle require oxygen? how is it dependent on ETC for its byproducts?
1 answer
Fri Apr 26, 2013 1:44 AM
Post by Kenshin Kenshin on April 25, 2013
Hi, I was wondering in the equilibrium section of the new pchem vids you were going to make are you going to go over the acid/base equilibrium rxn in the more in depth version for pchem compared to gen chem?
5 answers
Sun Apr 21, 2013 10:04 PM
Post by Brian Phung on April 21, 2013
Hi I was wondering if there would be any vid on signaling pathway?