Oxidative phosphorylation for medical school

OXIDATIVE PHOSPHORYLATION

V.S.RAVIKIRAN, MSc.,[email protected]

V.S.RAVIKIRAN, MSc., Dept. of Biochemistry, ASRAM Medical college, Eluru-

534005.AP, India

• Food : Food is the source of energy.• Energy : Energy is the capacity to do work.• Bioenergetics : is the quantitative study of

energy transformations that occur within the living cells.

• This follows the laws the thermodynamics.

• Thermodynamics : is a branch of physical sciences that deals with energy changes.

• First Law of Thermodynamics• Stated simply; The total energy of the

universe does not change. This does not mean that

the form of the energy cannot change.

• The internal energy of a system can change only by work or heat exchanges. From this the change in the free energy of a system can be shown by the following equation:

• ΔE = q – w• Where q is the heat absorbed by the system and w is

the work done.

• When q is negative heat has flowed from the system and when q is positive heat has been absorbed by the system.

• Entropy (S): is a measure of the degree of randomness or disorder of a system.

• Enthalpy (H) : is the heat content of a sytem.

• Second Law of Thermodynamics: Entropy• The second law of thermodynamics states that the

universe (i.e. all systems) tend to the greatest degree of randomization.

• For an isothermal reversible reaction the change in entropy can be reduced to the term:

• ΔS = ΔH/T

• ΔS = ΔH/T• In order to effectively evaluate the course

(spontaneity or lack there of) of a reaction and taking into account both the first and second laws of thermodynamics, Josiah Gibbs defined the term, free energy which is defined as:

• ΔG = ΔH – TΔS

• ΔG = ΔH – TΔS• ΔG = change in free energy.• ΔH = change in enthalpy or heat content of

the system.• ΔS = change in entropy.• T = absolute temperature.

• Useful energy is the form of energy that is capable of performing work.- two major types:- (1) Heat energy- (2) Free energy

• (1) Heat energy, which is capable of performing work through change of temperature.

• (2) Free energy which is capable of performing work at constant temperature.

• ΔG = ΔH – TΔS

• ΔG = ΔH – TΔS• Reactions with negative ΔG values are termed

exergonic and those with positive ΔG values endergonic.

• However, when a system is at equilibrium:ΔG = 0

• Exergonic reaction :• ATP + H2O → ADP + Pi: ΔGo' = –7.3 kcal/mol

• Endergonic reaction :• ADP + Pi → ATP : ΔGo' = +7.3 kcal/mol

• ΔG = ΔH – TΔS• Exothermic reaction = ΔH negative• Endothermic reaction = ΔH is positive• Iso-thermic reaction = ΔH is zero

• Standard free energy change (ΔGo’)• It is the free energy change under standard

conditions.• The standard conditions are as below:

Temperature of 250C (2980K), Pressure of 1.0 atm (760 mm Hg) pH of 7.0, Reactants and products are all present in their standard concentrations namely 1.0M.

Standard free energies of hydrolysis of some common metabolic intermediates

Metabolite ΔGo’

Phosphoenol pyruvate -14.8 High energy compoundsCarbamoyl phosphate -12.3

1,3-Bisphosphoglycerate -11.8

Acid phosphate -11.2

Creatine phosphate -10.3

Arginine phosphate -7.6

ATP to ADP + Pi -7.3 ΔGo’ = 0ATP to AMP + PPi -7.7 = equilibriumATP to AMP +Pi + Pi -14.6

Glucose 1-phosphate -5.0 Low energy compoundsGlucose 6-phosphate -3.3

Glycerol 1-phosphate -2.2

Phosphoenol pyruvate Pyruvate (ΔGo’ =-14.8 kcal/mol)

Metabolite ΔGo’Phosphoenol pyruvate

-14.8

ΔGo’ = (-) ΔGo’ = (+) ΔGo’ = (0)

ATPATP is the energy carrier for most

biological reactions

ATP + H2O -> ADP + PiATP + H2O -> AMP + PPi

19

Measurement of redox potentialX(oxidized) + X-(reduced) =redox couple

Samplehalf-cell

Standard referencehalf-cell

Electrons, but notX or X-, can flowthrough the agar bridge

If the reaction is,X- + H+ X + 1/2 H2

In half-cells:X- X + e- & H+ + e- 1/2 H2

21

Reduction potentials of biological redox couples

E’o = standard reduction potential

‘prime’ denotes pH 7‘zero’ denotes ‘standard’

Free Energy and Reduction Potential

Number of electrons transferred in the redox reaction Faraday’s constant (96485

J/volt/mole)

Crucial equation: Go' = -nF Eo'

The relative tendency to accept e-s and become reduced.

Reduction Potentials

= Eo'(acceptor) - Eo'(donor)

E0’=standard reduction potential.

If Eo' is positive, an electron transfer reaction is spontaneous (Go' <0)

The free energy of a typical reaction is calculated

directly from its Eo by the Nernst equation as shown ′

below, where n is the number of electrons involved

in the reaction and F is the Faraday constant (23.06

kcal/volt/mol or 94.4 kJ/volt/mol):

ΔG° = –′ nFΔEo′

Order and Reduction Potentials

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

+0.077

+0. 22 +0. 25

+0. 29 +0. 55

-0.32

+0.03

+0.045

+0.82

-0.3

28

ATP from Electron Transport

ΔG° = –′ nFΔEo′

∆Go’ = -2 X 23.06 X 1.14 = -52.6 Kcal/mol

nFΔEo = 1.14 V′

Oxidative Phosphorylation

Oxidative phosphorylation is the process by which the energy stored in NADH and FADH2 is used to produce ATP.

A. Oxidation step: electron transport chain

NADH + H+ + O2NAD+ + H2O

12

FADH2 + O212

FAD + H2O

The free energy available as a consequence of transferring 2 electrons from NADH or succinate to molecular oxygen is –52.6 and –36 kcal/mol, respectively.

–36 kcal/mol

–52.6 kcal/mol

Order and Reduction Potentials

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

+0.077

+0. 22 +0. 25

+0. 29 +0. 55

-0.32

+0.03

+0.045

+0.82

-0.3

Oxidative Phosphorylation

Oxidative phosphorylation is the process by which the energy stored in NADH and FADH2 is used to produce ATP.

A. Oxidation step: electron transport chain

NADH + H+ + O2NAD+ + H2O

12

FADH2 + O212

FAD + H2O

The free energy available as a consequence of transferring 2 electrons from NADH or succinate to molecular oxygen is –52.6 and –36 kcal/mol, respectively.

–36 kcal/mol

–52.6 kcal/mol

Burning glucose in an experiment

Energy released from glucose

(as heat and light)

100%

Energy released from glucose

banked in ATP

“Burning” glucosein cellular respiration

About 40%

Gasoline energy converted to movement

Burning gasolinein an auto engine

25%

How efficient is cell respiration?

Mitochondria

36

37

Oxidative Phosphorylation

Oxidative phosphorylation is the process by which the energy stored in NADH and FADH2 is used to produce ATP.

A. Oxidation step: electron transport chain

B. Phosphorylation step

NADH + H+ + O2NAD+ + H2O

12

FADH2 + O212

FAD + H2O

ADP + Pi ATP

Electron Carriers

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

NAD+ or FAD

There are 2 sites of entry for electrons into the electron transport chain:

Both are coenzymes for dehydrogenase enzymes

The transfer of electrons is not directly to oxygen but through coenzymes

40

46

Nicotinamide coenzymes: NAD+

N

CONH2

N

CONH2

H HXH2

X

oxidised coenzyme

NAD+ or NADP+reduced coenzymeNADH or NADPH

+ H+

Always a 2-electron reaction transferring 2 e- and 2 H+

48

FMN (Flavin mononucleotide)

FMN coenzyme:• Contains flavin,

ribitol,and a phosphate.

• Accepts 2H+ + 2e-

to form reduced coenzyme FMNH2.

The flavin coenzymes / flavoproteins

H3C

H3C NN

N O

O

N

CH2 CH CH CH CH2

OH OH OH

O P OH

OH

O

riboflavin monophosphate(flavin mononucleotide, FMN)

H3C

H3C NN

N O

O

N

CH2 CH CH CH CH2

OH OH OH

O P O P O

OH

O

OH

O

CH2 O

OH OH

N

N

NH2

N

N

flavin adenine dinucleotide (FAD)

FAD Always a 2-electron reaction transferring 2 e- and 2 H+

Oxidation and reduction of flavin coenzymes

it can accept/donate 1 or 2 e FMN has an important role in mediating e transfer between carriers that transfer 2 e (e.g., NADH) and those that transfer 1 e (e.g., Fe+++).

C

CCH

C

C

HC

NC

CN

NC

NHC

H3C

H3C

O

O

CH2

HC

HC

HC

H2C

OH

OPO-

O

O-

OH

OH

C

CCH

C

C

HC

NC

C

HN

NC

NHC

H3C

H3C

O

O

CH2

HC

HC

HC

H2C

OH

OPO-

O

O-

OH

OH

C

CCH

C

C

HC

NC

C

HN

NH

C

NHC

H3C

H3C

O

O

CH2

HC

HC

HC

H2C

OH

OPO-

O

O-

OH

OH

e + H+ e

+ H+

FMN FMNH2 FMNH·

Role of FMN mediating between 2e & 1e carriers:

For example, when NADH donates electrons to the respiratory chain, the initial electron transfers are:

NADH + H+ + FMN NAD+ + FMNH2

FMNH2 + Fe+++ FMNH· + Fe++ + H+

52

Iron-Sulfur (Fe-S) Clusters

Fe-S clusters:• Are groups of proteins containing iron ions and

sulfide. • Accept electrons to reduce Fe3+ to Fe2+, and lose

electrons to re-oxidize Fe2+ to Fe3+.

FeFe

S

S

S

Fe

Fe

S

S

S

SS

Cys

Cys

Cys

Cys

S

Fe

S

Fe

S

S

S

S

Cys

CysCys

Cys

Iron-Sulfur Centers

Ubiquinone

QCoenzyme Q CoQ

Other names and abbreviations:

FAD FeS

FeS

FeS

FMN

NAD+

ubiquinone

Cyt b

ubiquinone

O

O

C H 3 O

CH 3C H 3 O

( CH 2 CH C CH 2 ) n H

CH 3

O H

O H

C H 3 O

CH 3C H 3 O

( CH 2 CH C CH 2 ) n H

CH 3

2 e

+ 2 H +

c o e n z y m e Q

c o e n z y m e Q H 2

Most often n = 10Free CoQ can undergo a 2 e oxidation/reduction:Q + 2 e + 2 H+ QH2.

O

O

C H 3 O

CH 3C H 3 O

(CH 2 CH C CH 2 )n H

CH 3

O H

O H

C H 3 O

CH 3C H 3 O

(CH 2 CH C CH 2 )n H

CH 3

e + 2 H +

c o e n zy m e Q

c o e n zy m e Q H 2

O

O

C H 3 O

CH 3C H 3 O

(CH 2 CH C CH 2 )n H

CH 3e

c o e n zy m e Q •

When bound to special sites in respiratory complexes, CoQ can accept 1 e- to form a semiquinone radical (Q•-).

• Coenzyme Q (CoQ, Q or ubiquinone) is lipid-soluble. It dissolves in the hydrocarbon core of a membrane.

• the only electron carrier not bound to a protein.

• it can accept/donate 1 or 2 e-. Q can mediate e- transfer between 2 e- that transfer and 1 e- carriers

57

Coenzyme Q (Q or CoQ)

Coenzyme Q (Q or CoQ) is: • A mobile electron carrier derived from

quinone.• Reduced when the keto groups accept 2H+

and 2e-.

58

Cytochromes

Cytochromes (cyt) are:

• Proteins containing heme groups with iron ions.

Fe3+ + 1e- Fe2+

• Abbreviated as cyt a, cyt a3, cyt b, cyt c, and cyt c1.

Cytochromes

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

proteins that accept electrons from QH2 or FeS

Ultimately transfers the electrons to oxygen

Cytochromes are electron carriers containing hemes . Hemes in the 3 classes of cytochrome (a, b, c) differ in substituents on the porphyrin ring.

Some cytochromes(b,c1,a,a3) are part of large integral membrane protein complexes.

Cytochrome c is a small, water-soluble protein.

Cytochromes

The heme iron can undergo 1 e- transition between ferric and ferrous states: Fe3+ + e- Fe2+

Copper ions besides two heme A groups (a and a3) act as electron carriers in Cyta,a3 Cu2++e- Cu+

Heme is a prosthetic group of cytochromes. Heme contains an iron atom in a porphyrin ring system.

NAD+, flavins and Q carry electrons and H+

Cytochromes and non-haem iron proteins carry only electrons

NAD+ FAD undergoes only a 2 e- reaction; Cytochromes undergo only 1e- reactionsFMN Q undergoes 1e- and 2 e- reaction

Electron carriers

Electron Transport chain(respiratory chain)

• The electron transport chain in the inner mitochondrial membrane can be isolated in four proteins complexes(I, II, III, IV).

• A lipid soluble coenzyme (Q) and a water soluble protein (cyt c) shuttle between protein complexes

• Electrons transfer through the chain - from complexes I and II to complex IV

The electron transport chain

Mitochondrial Complexes

67

Electron Transport Chain

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

I

II

III IV

Mitochondrial Complexes

NADH Dehydrogenase

Succinate dehydrogenase

CoQ-cyt c Reductase

Cytochrome Oxidase

70

At Complex I, hydrogen and electrons are transferred from:

NADH to FMN.FMN + NADH + H+ FMNH2 + NAD+

FMNH2 to Fe-S clusters and Q, which reduces Q to QH2 and regenerates FMN.

Q + FMNH2 QH2 + FMN

Complex I to Complex III by Q (QH2), a mobile carrier.

Complex I NADH Dehydrogenase

73

At Complex II, hydrogen and electrons are transferred from:

FADH2 to Complex II, which is at a lower energy level than Complex I.

FADH2 to coenzyme Q, which reduces Q and regenerates FAD.Q + FADH2 QH2 + FAD

Complex II to Complex III by Q(QH2), a mobile carrier.

Complex IISuccinate Dehydrogenase

76

At Complex III, electrons are transferred from: QH2 to two Cyt b, which reduces Cyt b and

regenerates Q.2Cyt b (Fe3+) + QH2 2Cyt b (Fe2+) + Q + 2H+

Cyt b to Fe-S clusters and to Cyt c, the second mobile carrier.

2Cyt c (Fe3+) + 2Cyt b (Fe2+) 2Cyt c (Fe2+) + 2Cyt b (Fe3+)

Complex III CoQ-Cytochrome c reductase

79

Complex IV Cytochrome c Oxidase

At Complex IV, electrons are transferred from:

Cyt c to Cyt a..

2Cyt a (Fe3+) + 2Cyt c (Fe2+) 2Cyt a (Fe2+) + 2Cyt c

(Fe3+) Cyt a to Cyt a3, which provides the

electrons to combine H+ and oxygen to form water. 4H+ + O2 + 4e- (from Cyt a3) 2H2O

Complex Name No. of Proteins

Prosthetic Groups

Complex I NADH Dehydrogenase 46 FMN, 9 Fe-S centers

Complex II Succinate-CoQ Reductase 5 FAD, cyt b560, 3 Fe-S centers

Complex III CoQ-cyt c Reductase 11 cyt bH, cyt bL, cyt c1, Fe-SRieske

Complex IV Cytochrome Oxidase 13 cyt a, cyt a3, CuA, CuB

Support for this order of events

1. Energetically favorable. electrons pass from lower to higher standard reduction potentials.2. Spectra: the absorption spectrum for the reduced carrier differs from that of its oxidized form. carriers closer to oxygen are more oxidized.

3. Specific inhibitors. Those before the blocked step should be reduced and those after be oxidized.

4. Assay of individual complexes.NADH can reduce complex I but not the other complexes.

84

The chemiosmotic hypothesis

Electron transport through the respiratory chain leads to pumpingof protons from the matrix to the cytosolic side of the inner mitochondrial membrane.The pH gradient and membrane potential constitute a proton-motive force that is used to drive ATP synthesis.

pH outside is 1.4 unitslower than inside

Membrane potential is0.14V = G of 5.2 kcalper mole of protons

By Peter Mitchell, 1961

Order and Reduction Potentials

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

+0.077

+0. 22 +0. 25

+0. 29 +0. 55

-0.32

+0.03

+0.045

+0.82

-0.3

H+ Transport

Complex I, III, IV drive H+ transport from matrix to the cytosol When e- flow through, which creates proton gradient(electrochemical potential) across the inner membrane

Complex I and Complex IV : The mechanism of H+ transport is still not known.

The mechanism of H+ transport in Complex III is Q cycle.

4H+ are pumped per 2e passing through complex III.

The H+/eratio is less certain for the other complexes: probably 4H+/2e for complex I; 2H+/2e for complex IV.

Matrix

H+ + NADH NAD+

+ 2H+ 2H+ + ½ O2 H2O

2 e – –

I Q III IV

+ +

4H+ 4H+ 2H+ Intermembrane Space

cyt c

89

ATP synthase is composed of 3 fragments: F0, which is localized in the membrane; F1, which protrudes from the inside of the inner membrane into the matrix; and oligomycin sensitivity-conferring protein (OSCP), which connects F0 to F1.

90

ATP synthase

subunit

c ring subunit

subunit subunit

F1 subunit has 5 types ofpolypeptide chains(3, 3, , , ), displaysATPase activity

& are members of P-loop family

F0 contains the proton channel ring of 10-14 c subunits

‘a’ subunit bindsto outside of ring

Exterior columnhas 1 a subunit2 b subunits, &the subunit

Moving unit (rotor) is c ring & Remainder is stationary (stator)

91

ATP Synthase

In ATP synthase:• Protons flow back to

the matrix through a channel in the F0 complex.

• Proton flow provides the energy that drives ATP synthesis by the F1 complex.

108

ATP Synthase F1 Complex

In the F1 complex of ATP synthase:• A center subunit () is surrounded by three

protein subunits: loose (L), tight (T), and open (O).

• Energy from the proton flow through F0 turns the center subunit (), which changes the shape (conformation) of the three subunits.

109

ATP Synthesis in F1

During ATP synthesis:• ADP and Pi enter the loose L site.• The center subunit turns changing the L site to a

tight T conformation.• ATP is formed in the T site where it remains

strongly bound.• The center subunit turns changing the T site to

an open O site, which releases the ATP.

110

ATP Synthase F1 Diagram

There are three nucleotide-binding catalytic sites, located at interfaces but predominantly involving residues of the subunits.

Each subunit contains a tightly bound ATP, but is inactive in catalysis.

Mg++ binds with the adenine nucleotides in both & subunits.

F1 in cross

section

The binding change mechanism of energy coupling was proposed by Paul Boyer.

He shared the Nobel prize for this model that accounts for the existence of 3 catalytic sites in F1.

For simplicity, only the catalytic subunits are shown. It is proposed that an irregularly shaped shaft linked

to Fo rotates relative to the ring of 3 subunits.

The rotation is driven by flow of H+ through Fo.

ADP + Pi ATP

ATP

ATP ADP + Pi

ATP ADP + Pi

ATP open tight

binding

loose binding

repeat

Binding Change Mechanism

ADP + Pi ATP

ATP

ATP ADP + Pi

ATP ADP + Pi

ATP open tight

binding

loose binding

repeat

Binding Change Mechanism

The conformation of each subunit changes sequentially as it interacts with the rotating shaft. Each subunit is in a different stage of the catalytic cycle at any time. E.g, the green subunit sequentially changes to: a loose conformation in which the active site can

loosely bind ADP + Pi

a tight conformation in which substrates are tightly bound and ATP is formed an open conformation that favors ATP release. 

Bound to one subunit is a non-hydrolyzable ATP analog (assumed to be the tight conformation).

Bound to another subunit is ADP (loose). The third subunit has an empty active site (open).

This is consistent with the binding change model, whichpredicts that each subunit, being differently affected bythe irregularly shaped rotating shaft, will be in a different stage of the catalytic cycle.

ADP + Pi ATP

ATP

ATP ADP + Pi

ATP ADP + Pi

ATP open tight

binding

loose binding

repeat

Binding Change Mechanism

Additional data are consistent with an intermediate conformation between each of the 3 states shown. This intermediate conformation may have nucleotide bound at all 3 sites. By one model, in the left image above:ATP synthesis (on green subunit) is associated with transition to an intermediate conformation that allows binding of ADP + Pi to the previously empty site (magenta).A further conformational change then occurs as ATP formed in the previous step is released (from cyan subunit).

ADP + Pi ATP

ATP

ATP ADP + Pi

ATP ADP + Pi

ATP open tight

binding

loose binding

repeat

Binding Change Mechanism

P :O RATIO

• The P:O ratio is defined as the number of inorganic phosphate molecules incorporated into ATP for every atom of oxygen consumed.

• P:O ratio = NADH = 3• P:O ratio = FADH2 = 2

Transport of ATP, ADP, & Pi

ATP produced in the mitochondrial matrix must exit to the cytosol to be used by transport pumps, kinases, etc.

ADP & Pi arising from ATP hydrolysis in the cytosol must reenter the matrix to be converted again to ATP.

Two carrier proteins in the inner mitochondrial membrane are required.

The outer membrane is considered not a permeability barrier. Large outer membrane VDAC channels are assumed to allow passage of adenine nucleotides and Pi.

Adenine nucleotide translocase (ADP/ATP carrier) is an antiporter that catalyzes exchange of ADP for ATP across the inner mitochondrial membrane. At cell pH, ATP has 4 () charges, ADP 3 () charges. ADP3/ATP4 exchange is driven by, and uses up, membrane potential (one charge per ATP).

ADP + Pi ATP matrix lower [H+]

_ _

3 H+ ATP4 ADP3 H2PO4

H+

higher [H+] ADP + Pi cytosol

energyrequiring reactions

ATP4

+ +

Phosphate re-enters the matrix with H+ by an electroneutral symport mechanism. Pi entry is driven by, & uses up, the pH gradient (equivalent to one mol H+ per mol ATP).Thus the equivalent of one mol H+ enters the matrix with ADP/ATP exchange & Pi uptake. Assuming 3H+ transported by F1Fo, 4H+ total enter the matrix per ATP synthesized.

ADP + Pi ATP matrix lower [H+]

_ _

3 H+ ATP4 ADP3 H2PO4

H+

higher [H+] ADP + Pi cytosol

energyrequiring reactions

ATP4

+ +

Animation

126

Regulation of Electron Transport

In the electron transport system:• Low levels of ADP, Pi, oxygen, and NADH

decrease electron transport activity.• High levels of ADP activate electron

transport.

Name Function Site of Action

Rotenone e– transport inhibitor Complex I

Amytal e– transport inhibitor Complex I

Antimycin A e– transport inhibitor Complex III

Cyanide e– transport inhibitor Complex IV

Carbon Monoxide e– transport inhibitor Complex IV

Azide e– transport inhibitor Complex IV

2,4,-dinitrophenol Uncoupling agent transmembrane H+ carrier

Pentachlorophenol Uncoupling agent transmembrane H+ carrier

Oligomycin Inhibits ATP synthase OSCP fraction of ATP synthase

Inhibitors of Oxidative Phosphorylation

131

ATP Energy from Glucose

• The complete oxidation of glucose yields 6CO2, 6H2O, and 36 ATP.

132

In glycolysis: • Glucose forms 2 pyruvate, 2 ATP and 2NADH. • NADH produced in the cytoplasm cannot enter the

mitochondria. • A shuttle compound (glycerol-3-phosphate) moves

hydrogen and electrons into the mitochondria to FAD, which forms FADH2.

• Each FADH2 provides 2 ATP.

Glucose 2 pyruvate + 6 ATP

ATP from Glycolysis

133

ATP from Glycolysis

Reaction Pathway ATP for One GlucoseATP from GlycolysisActivation of glucose -2 ATPOxidation of 2 NADH (as FADH2) 4 ATP

Direct ADP phosphorylation (two triose) 4 ATP

Summary: C6H12O6 2 pyruvate + 2H2O + 6 ATP

glucose

134

• One turn of the citric acid cycle provides:3 NADH x 3 ATP = 9 ATP1 FADH2 x 2 ATP = 2 ATP1 GTP x 1 ATP = 1 ATP

Total = 12 ATPAcetyl CoA 2 CO2 + 12 ATP

• Because glucose provides two acetyl CoA , two turns of the citric acid cycle produce 24 ATP.2 Acetyl CoA 4 CO2 + 24 ATP

ATP from Citric Acid Cycle

135

One glucose molecule undergoing complete oxidation provides:From glycolysis 6 ATPFrom 2 Pyruvate 6 ATPFrom 2 Acetyl CoA 24 ATP

Overall ATP Production for One Glucose: C2H12O6 + 6O2 + 36ADP + 36Pi Glucose 6CO2 + 6H2O + 36ATP

ATP from Glucose

Substrate level phosphorylation

• The energy from a high energy compound is directly transferred to nucleotide di-phosphate to form a tri-phosphate without the help of electron transport chain (ETC).

• Example :- Bisphospho gylcerate kinase- Pyruvate kinase- Succinate thiokinase

C

C

CH 2 O PO 32

O O PO 32

H O H

C

C

CH 2 O PO 32

O O

H O H

A D P A T P

1

22

3 3

1

M g 2+

1 , 3 - b i s p h o s p h o - 3 - p h o s p h o g l y c e r a t e g l y c e r a t e

P h o s p h o g l y c e r a t e K i n a s e

C

C

CH 3

O O

O2

3

1A D P A T PC

C

CH 2

O O

O PO 32

2

3

1

p h o s p h o e n o l p y r u v a t e p y r u v a t e

P y r u v a t e K i n a s e

5- Succinyl CoA to succinateSuccinyl CoA to succinate Enzyme = succinyl CoA synthetase succinyl-CoA COO-

+ GDP + Pi CH2 + CoA-SH +

CH2 GTP

COO-

succinate 

-- substrate level phosphorylation-- GTP is equivalent to ATP; GTP toATP by nucleoside diphosphokinase

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