Biological ions and Oxid Phosp

8/3/2019 Biological ions and Oxid Phosp

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1

Biologic oxidations


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Biological Oxidation Involves the transfer of electrons:

oxidation being termed for the removal of

electrons& reduction for gain of electrons

Oxidation is always accompanied by reduction of ane- acceptor

Higher forms of lives completely rely on O2 for lifeprocesses i.e. respiration a process by which cellsderive energy with a controlled reaction between H+and O2; the end product being water.


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However there do occur large no. of reactions inliving system without the involvement of molecularO

2. The reactions are catalyzed by a set of enzymes

called as Dehydrogenases.

Other reactions do incorporate molecular O2 for thecompletion of reaction.

O2 is also required during treatment for respiratoryand cardiac failure for, the proper functioning ofboth require O2.


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Capturing energy from foods

requires the transfer of electrons Oxidation is the loss of electrons from one

molecule or atom to another. Reduction is the gain of electrons by one molecule

or atom from another.

Each intermediate compound in a biologicaloxidation is slightly more oxidized than its

precursor


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During a biological oxidation, energy is stored inthe form of the chemical bonds in adenosinetriphosphate (ATP).

The energy produced when ATP is broken downto ADP and phosphate is used to power manyprocesses in a cell.

Almost every chemical reaction in the cell eitherconsumes or produces ATP at some point.

The catabolic reactions in the cell are tightlycoupled to the biosynthetic reactions, forming thetwo sides of metabolism: releasing energy by

breaking things down and using energy to buildthin s u .


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The concept of the

biological oxidation


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The three stages of

biological oxidation


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MITOCHONDRIA

1.OUTER MEMBRANE MARKERS:

ACYL COA SYNTHETASE

GLYCEROLPHOSPHATE ACYL TRANSFERASE

2.INTERMEMBRANE SPACE:

ADENYLATE KINASE

CREATINE KINASE

3..INNER MEMBRANE,OUTER MEMBRANEGLYCEROL-3-PHOSPHATE DH

4..INNER MEMBRANE INNER MEMBRANE:

ELECTRON CARRIERS

SUCCINATE DHATP SYNTHASE

MEMBRANE TRANSPORTERS

5.MITOCHONDRIAL MATRIX MARKERS:

~ENZYMES OF OXIDATIVE PROCESSES:INSIDE MITOCHONDRIA.


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Enzymes involved in O/R

reactions Are k/as Oxidoreductases which includes : oxidases,

dehydrogenases, hydroperoxidaes and oxygenases.

Oxidases use oxygen as an electron acceptor

Dehydrogenases cant use as an electron acceptor

Hydroperoxidases use H2O2 as a substrate

Oxygenases catalyse the direct transfer of O2 into thesubstrate

Oxidases & dehydrogenases involved in respiration;hydroperoxidases neutralize free radicals & oxygenasesare involved in biotransformation


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14

Enzymes Involved in the

Oxidation reactions


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Oxidases Catalyze the removal of hydrogen from a substrate withthe involvement of oxygen as a H acceptor

Exist in two different forms :

some of them are copper containing as, Cytochromeoxidase - the terminal component of ETC which transferthe e - finally to O2.

Other are flavoproteins as , L aminoacid oxidase,xanthine oxidase


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Dehydrogenases Perform 2 main functions:1. Transfer hydrogen from one substrate to another in

a coupled O/R reaction2. As components of Electron transport chain

o Dehydrogenases use coenzymes nicotinamides &riboflavin - as hydrogen carriers


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Hydroperoxidases Includes 2 sets of enzymes : catalase and

peroxidases

Peroxidases reduce H2O

2at the expense of several

other substances

H2O2 + AH2 2H2O + A

o Catalase uses H2O2 as electron acceptor & electrondonor

2H2O2 2H2O

Peroxisomes are rich in oxidases and catalases


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Oxygenases Catalyse the incorporation of O2 into subtrates in 2

steps

- Oxygen is bound to the active site of the enzyme

- bound O2 is reduced or transferred to the substrate

Consists of two sets of enzymes

1. Dioxygenases : incorporate both atoms of oxygen intothe substrate ; A + O2 AO2

2. Monooxygenases : incorporates one atom of oxygeninto the substrate & the other is reduced to water

A H + O2 + ZH2 A OH + H2O + Z


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19

Mitochondrion oxidation

system


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Electron Transport andOxidative Phosphorylation


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An Overview

Biological oxidations are catalyzed by intracellular

enzymes. The purpose of oxidation is to obtain energy. Electron Transport: Electrons carried by reduced

coenzymes (NADH or FADH2) are passed sequentially

through a chain of proteins and coenzymes (so calledelectron transport chain)to O2 .

Oxidative Phosphorylation: Coupling e- Transport(Oxidation) and ATP synthesis (Phosphorylation) .

It all happens in mitochondrion or at the innermitochondrial membrane (eukaryotic cells)


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Impermeable to

ions and most

other compounds

In innermembrane

knobs

mitochondrionthe mitochondrion contained the enzymes responsiblefor electron transport and oxidative phosphorylation

Oxidative phosphorylation is a metabolic path a that ses


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Oxidative phosphorylation is a metabolic pathway that usesenergy released by the oxidation of nutrients toproduce adenosine triphosphate (ATP)

During oxidative phosphorylation, electrons are transferredfrom electron donors to electron acceptors(NAD/NADP+/FAD/FMN)

In eukaryotes, these redox reactions are carried out by a series

of protein complexes within mitochondria ,reactions areexergonic

These linked sets of enzymes are called electron transportchains

COMPONENTS OF ETC;

EXCEPT COQ, ALL MEMBERS ARE PROTEINs

SOME HAS Fe-S CENTRES

Fe RESIDUE COORDINATED WITH SH OF CYSTEINYL

CYTOCHROMES HAS PORPHYRIN RING WITH Fe IN CENTRE

CYT a+a3 HAS COPPER


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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 entryfor electrons into the

electron transport chain:

Both are coenzymes for

dehydrogenase enzymes

The transfer of electrons is not directly to oxygen but

through coenzymes


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Nicotinamide coenzymes: NAD+

N

CONH2

N

CONH2

H H

XH2

X

oxidised coenzyme

NAD+

or NADP+

reduced coenzyme

NADH or NADPH

+ H+

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


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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+


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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

O P O-

O

O-

OH

OH

C

CCH

C

C

H

C

NC

C

H

N

NC

NHC

H3C

H3C

O

O

CH2

HC

HC

HC

H2C

OH

O P O-

O

O-

OH

OH

C

CCH

C

C

H

C

NC

C

H

N

NH

C

NHC

H3C

H3C

O

O

CH2

HC

HC

HC

H2C

OH

O P O-

O

O-

OH

OH

e-

+H+

e-

+H+

FMN FMNH2FMNH


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

For example, when NADH donateselectrons to the respiratory chain, theinitial electron transfers are:

NADH + H+ + FMNNAD+ + FMNH2FMNH2 + Fe

+++FMNH + Fe++ + H+


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Iron-sulfur centers (Fe-S) are prosthetic groups containing 1-4 iron atoms

Iron-sulfur centers transfer only one electron, even ifthey contain two or more iron atoms.

E.g., a 4-Fe center might cycle between redox states:

Fe+++

3,Fe++

1(oxidized)+1 e-

Fe+++

2, Fe++

2(reduced)

Iron-sulfur Centers (clusters)


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Fe

Fe

S

S

S

Fe

Fe

S

S

S

S

S

Cys

Cys

Cys

Cys

S

Fe

S

Fe

S

S

S

S

Cys

CysCys

Cys

Iron-Sulfur Centers

NAD+


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Ubiquinone

QCoenzyme Q CoQ

Other names and abbreviations:

FAD FeS

FeS

FeS

FMN

ubiquinone

Cyt b

ubiquinone

O

O

CH3O

CH3CH3O

(CH2 CH C CH2)nH

CH3

OH

OH

CH3O

CH3CH3O

(CH2 CH C CH2)nH

CH3

2e-

+ 2H+

coenzyme Q

coenzyme QH2

Most often n = 10

Free CoQ can undergo a 2 e-oxidation/reduction:

Q + 2 e- + 2 H+ QH2.


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Coenzyme Q (CoQ, Q or ubiquinone) is

lipid-soluble. It dissolves in the hydrocarboncore 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


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Cytochromes

NAD

+

FMN

FeS

ubiquinoneFAD FeS

Cyt b


1/2 O2

ubiquinone

proteins that accept

electrons from QH2 or

FeS

Ultimately transfers the

electrons to oxygen


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Cytochromesare electron carrierscontaining hemes . Hemes in the 3 classesof cytochrome (a, b, c) differ in substituentson the porphyrin ring.

Some cytochromes(b,c1,a,a3) are part oflarge integral membrane proteincomplexes.

Cytochrome c is a small, water-solubleprotein.

Cytochromes


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The heme iron can undergo 1 e-

transitionbetween ferric and ferrous states: Fe3+ + e- Fe2+

Copper ions besides two heme A groups (aand a3) act as electron carriers in Cyta,a3

Cu2++e- Cu+

Heme is a prosthetic group ofcytochromes.Heme contains an iron atom in a porphyrin ringsystem.


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NAD+, flavins and Q carry electrons and H+

Cytochromes and non-haem iron proteins carry onlyelectrons

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

Electron carriers


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Electron Transport chain(respiratory chain)

The electron transport chain in the innermitochondrial membrane can be isolated infour proteins complexes(I, II, III, IV).

A lipid soluble coenzyme (Q) and a watersoluble protein (cyt c) shuttle betweenprotein complexes

Electrons transfer through the chain - fromcomplexes I and II to complex IV


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NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b


1/2 O2

ubiquinone

I

II

III IV

Mitochondrial Complexes

NADH Dehydrogenase

Succinate

dehydrogenase

CoQ-cyt c Reductase

Cytochrome Oxidase


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The electron transport chain

MitochondrialComplexes

NADH Ubi i O id d t


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NADH:Ubiquinone OxidoreductaseComplex I

One of the largest macro-molecular assemblies inthe mammalian cell

Over 40 different polypeptide chains, encoded by

both nuclear and mitochondrial genes

NADH binding site in the matrix side

Non-covalently bound flavin mononucleotide (FMN)

accepts two electrons from NADH Several iron-sulfur centers pass one electron at

the time toward the ubiquinone binding site


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NADH:Ubiquinone Oxidoreducase is aProton Pump

Transfer of two electrons from NADH to uniquinone is

accompanied by a transfer of protons from the matrix (N)

to the inter-membrane space (P)

Experiments suggest that about four protons are

transported per one NADH

NADH + Q + 5H+N = NAD+ + QH2 + 4 H

+P

Reduced coenzyme Q picks up two protons

S i t D h d


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Succinate DehydrogenaseComplex II

FAD accepts two electrons from succinate

Electrons are passed, one at a time, via iron-

sulfur centers to ubiquinone that becomes

reduced QH2


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Complex II: succinate-coenzyme Q reductase(succinate dehydrogenase)

The only TCA cycle enzyme that is an integral membraneprotein, also called flavoprotein (FP2).

Succinate fumarate + 2H+ + 2e-

UQ + 2H + + 2e- UQH2

Components: FAD and Fe-S centers

No proton pumped

Cytochrome bc Complex


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Cytochrome bc1 ComplexComplex III

Uses two electrons from QH2 to reduce twomolecules of cytochrome c

CoQ passes electrons to cyt c (and pumps H+)in a unique redox cycle known as the Q cycle


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The Q Cycle

Experimentally, four protons are transportedacross the membrane per two electrons that reachcyt. c

Two of the four protons come from QH2 The Q cycle provides a good model that explains

how two additional protons are picked up from thematrix

Cytochrome Oxidase


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Cytochrome OxidaseComplex IV

Mammalian cytochrome oxidase is a membrane

protein with 13 subunits

Contains two heme groups

Contains copper ions

Two ions (CuA) form a binuclear center

Another ion (CuB) bonded to heme forms Fe-

Cu center


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48


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Order and Reduction Potentials


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Order and Reduction Potentials

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b


1/2 O2

ubiquinone

+0.077

+0. 22 +0. 25

+0. 29 +0. 55

-0.32

+0.03

+0.045

+0.82

-0.3

Peter D. Mitchell proposed the chemiosmotic hypothesis in 1961.The
http://en.wikipedia.org/wiki/Peter_D._Mitchellhttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Peter_D._Mitchellhttp://en.wikipedia.org/wiki/Peter_D._Mitchellhttp://en.wikipedia.org/wiki/Peter_D._Mitchellhttp://en.wikipedia.org/wiki/Peter_D._Mitchellhttp://en.wikipedia.org/wiki/Peter_D._Mitchellhttp://en.wikipedia.org/wiki/Peter_D._Mitchell


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theory suggests essentially that most ATP synthesis in respiring cellscome from the electrochemical gradient across the inner membranes ofmitochondria by using the energy ofNADH and FADH2 formed from the

breaking down of energy rich molecules such as glucose.

Molecules such as glucose are metabolized to produce acetyl CoAas anenergy-rich intermediate. The oxidation of acetyl CoA in themitochondrial matrix is coupled to the reduction of a carrier molecule

such as NAD and FAD. The carriers pass electrons to the electrontransport chain (ETC) in the inner mitochondrial membrane, which inturn pass them to other proteins in the ETC. The energy available in theelectrons is used to pump protons from the matrix across the innermitochondrial membrane, storing energy in the form of a

transmembrane electrochemical gradient. The protons move back acrossthe inner membrane through the enzyme ATP synthase. The flow ofprotons back into the matrix of the mitochondrion via ATP synthaseprovides enough energy for ADP to combine with inorganic phosphateto form ATP. The electrons and protons at the last pump in the ETC are

taken up by oxygen to form water.

This was a radical proposal at the time and was not well
http://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Electrochemicalhttp://en.wikipedia.org/wiki/Mitochondrionhttp://en.wikipedia.org/wiki/NADHhttp://en.wikipedia.org/wiki/Flavin_grouphttp://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Acetyl_CoAhttp://en.wikipedia.org/wiki/Oxidationhttp://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotidehttp://en.wikipedia.org/wiki/FADhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electrochemical_gradienthttp://en.wikipedia.org/wiki/ATP_synthasehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Phosphatehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/ATP_synthasehttp://en.wikipedia.org/wiki/ATP_synthasehttp://en.wikipedia.org/wiki/ATP_synthasehttp://en.wikipedia.org/wiki/Electrochemical_gradienthttp://en.wikipedia.org/wiki/Electrochemical_gradienthttp://en.wikipedia.org/wiki/Electrochemical_gradienthttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/FADhttp://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotidehttp://en.wikipedia.org/wiki/Oxidationhttp://en.wikipedia.org/wiki/Acetyl_CoAhttp://en.wikipedia.org/wiki/Acetyl_CoAhttp://en.wikipedia.org/wiki/Acetyl_CoAhttp://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Flavin_grouphttp://en.wikipedia.org/wiki/Flavin_grouphttp://en.wikipedia.org/wiki/NADHhttp://en.wikipedia.org/wiki/Mitochondrionhttp://en.wikipedia.org/wiki/Electrochemicalhttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Adenosine_triphosphate


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This was a radical proposal at the time, and was not wellaccepted. The prevailing view was that the energy of electrontransfer was stored as a stable high potential intermediate, a

chemically more conservative concept.

The problem with the older paradigm is that no high energyintermediate was ever found, and the evidence for protonpumping by the complexes of the electron transfer chain grew too

great to be ignored. Eventually the weight of evidence began tofavor the chemiosmotic hypothesis, and in 1978, Peter Mitchellwas awarded the Nobel Prize in Chemistry.

Chemiosmotic coupling is important for ATP production inchloroplastsand many bacteria.

The proton-motive force
http://en.wikipedia.org/wiki/Electron_transfer_chainhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Chloroplasthttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Chloroplasthttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistryhttp://en.wikipedia.org/wiki/Electron_transfer_chainhttp://en.wikipedia.org/wiki/Electron_transfer_chainhttp://en.wikipedia.org/wiki/Electron_transfer_chainhttp://en.wikipedia.org/wiki/Electron_transfer_chainhttp://en.wikipedia.org/wiki/Electron_transfer_chain


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In all cells, chemiosmosis involves the proton-motive force(PMF) in some step. This can be described as the storing of

energy as a combination of a proton and voltage gradient acrossa membrane. The chemical potential energy refers to thedifference in concentration of the protons and the electricalpotential energy as a consequence of the charge separation(when the protons move without a counter-ion).In most cases

the proton motive force is generated by an electron transportchain which acts as both an electron and proton pump, pumpingelectrons in opposite directions, creating a separation of charge.In the mitochondria, free energy released from the electron

transport chain is used to move protons from the mitochondrialmatrix to the intermembrane space of the mitochondrion.

Moving the protons to the outer parts of the mitochondrion


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Moving the protons to the outer parts of the mitochondrioncreates a higher concentration of positively charged particles,resulting in a slightly positive, and slightly negative side (then

electrical potential gradient is about -200 mV (inside negative).This charge difference results in an electrochemical gradient.This gradient is composed of both the pH gradient and theelectrical gradient. The pH gradient is a result of the H+ ionconcentration difference. Together the electrochemical gradient

of protons is both a concentration and charge difference and isoften called the proton motive force (PMF). In mitochondria thePMF is almost entirely made up of the electrical component butin chloroplasts the PMF is made up mostly of the pH gradient.

In either case the PMF needs to be about 50 kJ/mol for the ATPsynthase to be able to make ATP


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ATP synthase

Two parts: F1 and F0 (latter was originally "F-o" forits inhibition by oligomycin)

---F1: ATP synthesis, a3b3gde

---Fo: Proton channel in inner membrane,ab2c10-12

Binding change mechanism: the three catalytic bsubunits are intrinsically identical but are not

functionally equivalently at any particular momentwhere they cycle through three conformationalstates.

Proton diffusion through the protein drivesATP synthesis!

Mitochondrial ATP Synthase


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Mitochondrial ATP SynthaseComplex

The proton-motive force causes rotation of the

central shaft g

This causes a conformational change within all thethree ab pairs

The conformational change in one of the three

pairs promotes condensation of ADP and Piinto

ATP


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NARP syndrome : point mutation at nucleotide 8993 on thegene encoding subunit 6 of mitochondrial ATP Synthase.

The symptoms included developmental delay, retinitis pigmentosa,dementia, seizures, ataxia, proximal neurogenic muscle weakness,and senory neuropathy, in a pedigree consistent with maternaltransmission .

INHIBITORS AND UNCOUPLERS

INHIBITORS OF ETC

COMPLEX I: COMPLEX II COMPLEX IIICOMPLEX IV

Rotenone Carboxin AntimycinCyanide,H2S

Amobarbital TTFA


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Inhibitors of electron transport andoxidative phosphorylation

Complex IV

Complex II

Complex I or III


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Drugs that inhibit the ETC

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b


1/2 O2

ubiquinone

I

II

III IV

Amytal

rotenone

Antimycin A

CN- CO

Rotenone helps natives of theAmazon rain forest catch fish!

binding tightly to the ferric form(Fe3+) of a3

Inhibitors and Artificial


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Inhibitors and ArtificialElectron Acceptors

Rotenoneamytal Antimycin A CN-,CO

Methyleneblue +0.01

Ferricyanide+0.36

INHIBITORS OF OXIDATIVE PHOSPHORYLATION


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ATRACTYLOSIDE(BLOCK MOVEMENT OF ATP & ADP)

OLIGOMYCIN(BLOCK FLOW OF H+ THROUGH Fo)

BONGREGATE(SAME AS ATRACTYLOSIDE)

IONOPHORE

(LYPOPHILIC MOLECULE) example: 1. VALINOMYCIN(MOBILE ION CARRIER), 2. GRAMICIDIN (CHANNELFORMER)

UNCOUPLERS OF OXIDATIVE PHOPHORYLATION

2,4 DINITROPHENOL2,4 DINITROCRESOLCCCP (MOST ACTIVE)chloro carbonyl cyanide phenyl hydrazoneDICOUMAROL(vit. K analogue)VALINO MYCIN

CALCIUM

PHYSIOLOGICAL UNCOUPLERS


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PHYSIOLOGICAL UNCOUPLERS

UCP1(THERMOGENIN) ACTIVATION OF FATTY ACID OXIDATIO

HEAT PRODUCTIO IN BROWN ADIPOSE TISSU

EXCESSIVE THYROID HORMONE

EFA DEFICIENCY

LONG CHAIN FATTY ACIDS IN ADPOSE TISSUE

CONJUGATED HYPERBILIRUBINEMIA

Reduction Potentials


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Number of electrons

transferred in the

redox reaction

Faradays constant

(96485 J/volt/mole)

Crucial equation:

Go' = -nF Eo'

The relative tendency to accept e-s and becomereduced.

Reduction Potentials

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

E0=standard reduction potential.

IfEo' is positive, an electron transfer reaction is

spontaneous (Go'


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Fumarate+2H++2e- succinate 0 031


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Fumarate+2H +2e succinate 0.031

FAD+ 2H++2e- FADH2 0

NAD++ 2H++2e- NADH+H+ -0.32

Succinate+FAD Fumarate+ FADH2

G' = - n F E'

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

G =-2*96485*(0-0.031)= 5.98KJ/mol

Succinate+ NAD+ Fumarate+ NADH+H+

G

=-2*96485*(-0.32- 0.031)= 67.7KJ/mol


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Removal of H across a C-C bond is notsufficiently exergonic to reduce

NAD+,but it does yield enough energyto reduce FAD.

Thats why succinate dehydrogenase

uses FAD other than NAD+

as coenzyme.

Documents

Biological ions and Oxid Phosp