18.oxidative phosphorylation
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OXIDATIVE PHOSPHORYLATION
DEFINITION
Oxidative phosphorylation is the name given to the synthesis of ATP from ADP ( phosphorylation), that occurs when NADH and FADH2 are oxidized by electron transport throughout the respiratory chain (hence called oxidative)
Mitochondria are the site of oxidative phosphorylation in eukaryotes ,
There is two ways to synthesize ATP
Oxidative phosphorylation : the phosphorylation of ADP to ATP coupled
to electron transfer
Substrate level phosphorylation : direct transfer the phosphate from chemical intermediate (also called substrate ) to ADP or GDP forming ATP or GTP , independent of electron transfer chain
Example of Substrate level phosphorylation
3-phosphoglycerate
1) 1,3-bisphosphoglycerate
ADP
ATP
Phosphoglycerate kinase
Glycolysis
2) Phosphoenolpyruvate
ADP
ATP
Pyruvate
Pyruvate kinase
3) succinyl CoA
GDP
GTP
succinate
succinyl CoA synthetase
Glycolysis
TCA cycle
CHEMIOSMOTIC HYPOTHESIS
Is the mechanism of oxidative phosphorylation ,
proposed by Peter Mitchell in 1961
The chemiosmotic hypothesis : it proposed that energy liberated by electron
transport is used to create a proton gradient across the mitochondrial inner membrane
and it is this proton gradient is used to drive ATP synthesis
Thus the proton gradient couples electron transport and ATP synthesis
ATP SYNTHASE Also called complex Ⅴ
It is the enzyme that actually synthesize ATP
It located in the inner mitochondrial membrane
It utilizes energy from the proton gradient to promote phosphorylation of ADP forming ATP
THE STRUCTURE OF ATP SYNTHASE The ATP synthase can be seen as spherical projections
from the inner membrane .
Is composed of two major components part ,
F1 unit or called F1 ATPase :
is the spheres of the ATP synthase
and point outward
F0 unit :
spans the inner mitochondria membrane
So the ATP synthase is also called F0F1 ATPase
The stalk between F0 and F1 contains several additional polypeptide
F1 unit
F0 unit
Proton channel
Matrix
Intermembran space
The structure of ATP synthase
F1 unit : contains 5 polypeptides in the form α3β3γδε.
only F1 components can hydrolyze ATP, have ATPase activity , so also called ATPase ,
F1 with F0 together can synthesize ATP
F0 unit: made of abc polypeptides, is proton channel, can be seen as the proton transport ,
The complete complex harnesses the energy released by electron transport to drive ATP synthesis
The function of ATP synthase
In summary : the oxidative phosphorylation process is as follow
Electron transport down the respiratory chain from NADH or FADH2
Complex , , Cause protons be pumped out Ⅰ Ⅲ Ⅳof the mitochondrial matrix into the intermembrane space
The pumping out of H+ generates a higher concentration of H+ and an electrical potential , thus an electrochemical proton gradient is formed .
The H+ flow back into the mitochondrial matrix through ATP synthase and the electrochemical proton gradient drives ATP synthesis
ELECTROCHEMICAL PROTON GRADIENT
Is the sum of chemical gradient : a higher concentration of H+ ions form the chemical
gradient of H+ outer : high concentration H+ inner : low concentration H+
Electrical potential : electrical charge potential across the inner mitochondrial
membrane outer: positive charge inner: negative charge
matrix
+ + + +
- - - -
H+
O2
H2O
H+
e-
ADP+
Pi ATP
The chemiosmotic hypothesis :
High H+Positive charge
Low H+Negitive charge
ⅢⅠ Ⅱ Ⅳ
F0
F1
Cyt c
Q
NADH+H+
NAD+
Fumarate
Succinate
H+
1/2O2+2H+
H2O
ADP+Pi ATP
H+
H+
H+
Intermembrane space
mattix
+ + + + + + + + + +
- - - - - - - - -
The chemiosmotic hypothesis :
GENERATE ATP SUMS
3 ATP are synthesized per NADH oxidized through the NADH
respiratory chain
2 ATP are synthesized per FADH2 oxidized through the FADH2
respiratory chain
WHY ATP SYNTHESIZE FROM FADH2 RESPIRATORY CHAIN IS LESS THAN NADH RESPIRATORY CHAIN ?
NADH respiratory have 3 H+ pump, complex , ,Ⅰ Ⅲ Ⅳ
FADH2 respiratory only have 2 H+ pump, complex ,Ⅲ Ⅳ
So the ATP made from FADH2 is less than from NADH
The process of biological oxidation
COUPLING OF ELECTRON TRANSPORT AND PHOSPHORYLATION
Electron transport is normally tightly coupled to ATP synthesis
electrons do not flow through the electron transport chain to oxygen unless ADP is simultaneously phosphorylated to ATP
Also , ATP is not synthesized unless electron transport is occurring to provide the proton gradient
Thus we can know that oxidative phosphorylation needs NADH or FADH2 , oxygen , ADP , and inorganic phosphate
COUPLING SITE OF ELECTRON TRANSPORT AND PHOSPHORYLATION
complex , ,Ⅰ Ⅲ Ⅳ
How to know this ?
P:O ratio: in oxidative phophorylation the P:O ratio is the number of ATP formed per oxygen atom is consumed
NADH respiratory chain : P:O ratio=3
forming 3 ATPs per oxygen atom consumed ,
NADH respiratory chain have 3 coupling site
FADH2 respiratory chain : P:O ratio=2
forming 2 ATPs per oxygen atom consumed ,
FADH2 respiratory chain have 2 coupling site
UNCOUPLERS
WHAT IS UNCOUPLERS? Some chemicals act as uncoupling agents,
that is, when added to cell, they stop ATP synthesis but electron transport still continues and so oxygen is still consumed
The chemicals for example : • 2,4-dinitrophenol (DNP) • uncoupling protein
DNP DNP are lipid-soluble small molecule
that can bind H+ ion and transport the H+ across the mitochondria membrane ,
So it is H+ ionophores
HOW DNP UNCOUPLING ? electron transport occurs and pump out H+ ions across
the inner mitochondrial membrane to build the H+ gradient .
But DNP in the same membrane carriers the H+ ions back into the mitochondrion , preventing formation of a proton gradient.
Since no proton gradient forms, so no ATP can be made by oxidative phosphorylation
the energy derived from electron transport is released as heat
UNCOUPLING PROTEIN There is brown adipose tissue in the body ,
this tissue is rich in mitochondria, the inner mitochondrial membranes of which contains a protein called uncoupling protein or thermogenin
HOW UNCOUPLING PROTEIN WORK ? Uncoupling protein can be seen as a H+ passageway
, allows H+ to flow back into mitochondria without having to enter the ATP synthase ,
thus preventing formation of a proton gradient , so uncouples electron transport and oxidative phosphorylation ,
And also energy derived from electron transport is released as heat
mechanism of uncoupling protein （ brown adipose tissue mitochondrial ）
Ⅲ ⅢⅠ Ⅰ Ⅱ Ⅱ
FF0 0
FF1 1
Ⅳ Ⅳ
Cyt c
Q
Intermembrane space
Matrix
Uncoupling protein
Heat energy HH+ +
HH+ + ADP+Pi ATP
THERMOGENESIS
The production of heat by uncoupling is called nonshivering thermogenesis .
It is important in certain biological situation ,
For example ,the brown adipose tissue is found in sensitive body areas of some new brown animals (including human ), where the heat production provides protection from cold condition
In addition, thermogenesis by brown adipose tissue plays a important role in maintaining body temperature in hibernating animals
RESPIRATORY CONTROL
ADP: The actual rate of oxidative phosphorylation is set by
the availability of ADP
If ADP is added to mitochondrial, the rate of oxygen consumption rises as electrons flow down the chain
Then when all the ADP has been phosphorylated to ATP, the rate of oxygen consumption falls
This process called respiratory control
this mechanism ensures that electrons flow down the chain only when ATP synthesis is needed.
If the level of ATP is high ,ADP is low,
no electron transport occurs
NADH and FADH2 build up,
so does excess citrate
then the citric acid cycle and glycolysis are all inhibited
OVER ALL ADP high
Oxidative phosphorylation rises Oxygen consumption rises
ADP low
Oxidative phosphorylation falls Oxygen consumption falls
ATP
Adenosine triphosphate: ATP
Glycosidic bond
NO
CH2O
OHOH
N
NN
NH2
P
O
OH
OP
O
OH
OP
O
OH
OH
ATPATP
Ester bond
αβr
Ribose
Adenine
Production and application of ATP
ATP
ADP
oxidative Phosphorylation
~P ~P
~P ~P
Mechnism energyOsmotic energyChemical energyElectric energyHot energy
substrate level Phosphorylation
RIOXIDATION OF CYTOSOLIC NADH
The inner membrane of mitochondria impermeable to some molecule and ions
Permeable to : pyruvate 、 succinate 、 citrate α-ketoglutarate 、 malate 、 Glu ect
Impermeable to : H+ 、 NADH 、 NADPH 、 oxaloacetate ect
The inner mitochondrial membrane is impermeable to NADH.
Therefore NADH produced in the cytoplasm during glycolysis go into the mitochondria through the membrane shuttle , then in the mitochondria go into the respiratory chain .
The membrane shuttle is a combination of enzyme reaction that bypass this impermeability barrier
WHICH REACTION OF GLYCOLYSIS PRODUCE NADH
Glyceraldehyde 3-phosphate
1,3-bisphosphoglycerate
Glyceraldehyde 3-phosphate
Dehydrogenase
NAD+
NADH
The reaction take place in the cytosol
THERE IS TWO SHUTTLE SYSTEM IN THE MITOCHONDRIAL MEMBRANE
• glycerol 3-phosphate shuttle
• Malate-asparate shuttle
NADH+H+
Glycerol 3-phosphate
Dehydrogenase
FADH2
NAD+ FAD
innerMembrane
electron chain
Dihydroxyacetone Phosphate
Glycerol 3-phosphate
• glycerol 3-phosphate shuttle
Glycerol 3-phosphate
Dehydrogenase
Dihydroxyacetone Phosphate
Cytosol
Glycerol 3-phosphate
NADH+H+
Glycerol 3-phosphate
Dehydrogenase
FADH2
NAD+
FAD
innerMembrane outer
Membrane
IntermembraneSpace
matrix
electron chain
Dihydroxyacetone Phosphate
PiCH2O-
CH2OH
C=O
PiCH2O-
CH2OH
C=O
Glecerol 3-phosphate
PiCH2O-
CH2OH
CHOH
PiCH2O-
CH2OH
CHOH
• glycerol 3-phosphate shuttle
Glycerol 3-phosphate
Dehydrogenase
Dihydroxyacetone phosphate in the cytosol is
reduced to glycerol -3-phosphate ,
and NADH reoxidized to NAD+,
by cytosolic glycerol 3- phosphate dehydrogenase
The glycerol -3-phosphate diffuse across the inner mitochondrial membrane
In the inner membrane the glycerol 3-phosphate is converted back to dihydroxyacetone phosphate by
mitochondrial glycerol 3-phosphate dehydrogenase
the mitochondrial glycerol 3-phosphate dehydrogenase does not use NAD+ but instead uses FAD.
The FADH2 is then reoxidized by FADH2 respiratory chain.So 2 ATPs are synthesized )
The dihydroxyacetone phosphate then diffuse back to the cytosol .
Note :
The shuttle does not allow cytoplasm NADH to enter the mitochondrion,
but transports the two electrons from NADH into the mitochondria
and feed the electron into the FADH2 electron transport chain .
So synthesize 3ATPs
NADH +H+
NAD+ malate
α-ketoglutaratecarrier
malate dehydrogenase
inner memebrane malateMalate
Oxaloacetate Oxaloacetate
NAD+
NADH +H+
malate dehydrogenase
glutamate –aspartate
carrier
Aspartate
Aspartate Aminotransferase
Aspartate Aminotransferase
Aspartate
glutamate
α-ketoglutarate
α-ketoglutarate
glutamate
Cytosol
NADH +H+
NAD+
-OOC-CH2-C-COO-
O
-OOC-CH2-C-COO-
OH
H
NADH +H+
NAD+
glutamate –aspartate
carrier
malateα-ketoglutarate
carrier
-OOC-CH2-C-COO-
OH
H
malate
-OOC-CH2-C-COO-
O
oxaloacetate
-OOC-CH2-CH2-C-COO-
O
-OOC-CH2-CH2-C-COO-
O
-OOC-CH
2-CH
2-C-COO
-
H3N
+
Hglutamate
malate dehydrogenase
aspartate aminotransferase
intermembrane space
inner memebrane
matrix
-OOC-CH
2-C-COO
-
H3N
+
Hasparate
-OOC-CH
2-C-COO
-
H3N
+
H
-OOC-CH
2-CH
2-C-COO
-
H3N
+
H
α-ketoglutarate
malate
Oxaloacetate in the cytosol is converted to malate by cytosolic malate dehydrogenase.
NADH oxidized to NAD+
The malate enters the mitochondrion by amalate-α-ketoglutarate carrier in the inner
mitochondrial membrane
In the matrix the malate is reoxidized to oxaloacetate , NAD+ form NADH.
Then NADH go into the NADH respiratory chain And 3ATPs are synthesized
Oxaloacetate does not easily cross the inner mitochondrial membrane and so is transaminated to form aspartate
And then the aspartate exits from the mitochondrion and is reconverted to oxaloacetate in cytosol , again by transamination
this cycle of reactions is to transfer the electrons from NADH in the cytosol to NADH in the mitochondrial matrix ,
The NADH in the mitochondria is then reoxidized by the NADH electron transport chain
So synthesize 3ATPs
Note
In summary : Cytosol NADH go into the mitochondria by this two shuttele
• glycerol 3-phosphate shuttle
in the mitochondria go into the FADH2
respiratory chain .
so produce 2 ATPs
Malate-asparate shuttle:
in the mitochondria go into the NADH respiratory chain. so produce 3ATPs
Complex : NADH dehydrogenaseⅠ or called NADH-CoQ reductase
complex : Succinate-coenzyme Q reductase Ⅱcomplex : Cytochrome bc1 complexⅢ or called cytochrome reductase
complex : Cytochrome oxidase Ⅳ
1. Description Composition of respiratory chain complex
Practice exercises
NADH
CoQ
succinateFAD(Fe-S)
FMN(Fe-S)
complexⅠ
complexⅡ
O2Cyt
c
Cytaa3
CuCuB
Cytb 、 Fe-S 、 Cytc1
Complex Ⅲ
Complex Ⅳ
2. Write down the two respiratory chain
FADH2 respiratory chain
NADH respiratory chain
3. Filling the blank
There is two respiratory chain in the body : that is ( ) and ( )
NADH respiratory chain
FADH2 respiratory chain
4. Explain : electron transport chain
Electron transport chain:
The electrons are transferred from NADH to oxygen along a chain of electron carriers collectively called electron transport chain , also called respiratory chain.
5. Choice the sequence of Cytochoreme in respiratory chain A . c c1 b aa3 O2
B . c1 c b aa3 O2
C. b c1 c aa3 O2
D. b c c1 aa3 O2
E. c b c1 aa3 O2
6. ROTENONE INHIBIT ELECTRON TRANSPORT AT ( )
A. NADH dehydrogenaseB. cytochrome bc1 complexC. cytochrome oxidase D. Succinate –Q dehydrogenase E. cytochrome c
( A )
7. ANTIMYCIN A INHIBIT ELECTRON TRANSPORT AT ( )
• A. NADH dehydrogenase
• B. cytochrome bc1 complex
• C. cytochrome oxidase
• D. Succinate –Q dehydrogenase
• E. cytochrome c
( B )
8. CARBON MONOXIDE (CO) INHIBIT ELECTRON TRANSPORT AT ( )
• A. NADH dehydrogenase
• B. cytochrome bc1 complex
• C. cytochrome oxidase
• D. Succinate –Q dehydrogenase
• E. cytochrome c
( C )
9. COUPLING SITE OF ELECTRON TRANSPORT AND PHOSPHORYLATION ARE( )
A. complex Ⅰ B. complex Ⅱ C. complex Ⅲ D. complex Ⅳ E. complex Ⅴ
( A,C,D )
10. THE TWO WAYS TO SYNTHESIZE ATP ARE ( ) AND ( )
-Oxidative phosphorylation -substrate level phosphorylation
11. THE MECHANISM OF OXIDATIVE PHOSPHORYLATION IS ( )
-Chemiosmotic hypothesis
12. THE ENZYME THAT ACTUALLY SYNTHESIS ATP IS ( ), IT IS MADE UP OF ( )UNIT AND ( ) UNIT
ATP synthase F0 , F1
13. NADH PRODUCED IN THE CYTOPLASM MUST BE REOXIDIZED VIA A MEMBRANE SHUTTLE . THE TWO SHUTTLE SYSTEM ARE ( ) AND ( )
-glycerol 3-phosphate shuttle
-Malate-asparate shuttle
14 . If ADP is high, The Oxidative phosphorylation and Oxygen consumption will ( ) .
if ADP is low , The Oxidative phosphorylation and Oxygen consumption will ( )
rises , falls
15 . the chemicals that can uncouple the electron transport with the ATP synthesis are ( ) and ( )
DNP, Uncoupling protein
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