The Electron Transport Chain

7/27/2019 The Electron Transport Chain

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ETC in:

Eukaryotescollection of moleculesembedded in the inner membrane ofmitochondria

Cristae- infoldings of the inner membrane

Prokaryotesfound in the plasma

membrane. Most components are proteins in nature.

Multiprotein complexes(1 to 4)

Contain prosthetic groups


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During electron transportelectron

carriers alternate between reduced and

oxidised. Entry of electron in an EC from uphill

ECreduced

Exit of electron from an EC to downhillECoxidised.

DownhillECmore electronegativethan their uphill EC.


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NADH from glycolysis and krebscycletransfer electrons to Complex 1.

Complex 1flavoprotein, named afterits prosthetic group, flavinmononucleotide(FMN)

Flavoprotein oxidises when passingelectrons to an iron-sulfur protein (Fe-s incomplex 1)


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FADH2reduced product of Citric acid

cycle

Transfers electrons to complex 2 Complex 2lower energy level than

complex 1


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Not a protein

Small and hydrophobic in nature

Individually mobile within the membrane Fe-S group of complex 1 and 2 transfer

their electrons to ubiquinone.

The latter is reduced while the 2complexes return back to their oxidizedstate


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Remaining carriers between ubiquinoneand water.

Protein in nature

Prosthetic groupheme ETC has different kinds of cytochromes,

different proteins with slightly different hemegroups also.

cyta3last cytochrome, gives electrons tofinal acceptorOxygen

A pair of hydrogen ions is also picked up foreach oxygen atom forming water.


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ATP synthaseenzyme that makes ATP fromADP and pi

In eukaryotesfound embedded in the inner

membrane of mitochondria In prokaryotesin plasma membrane ATP synthasemakes use of existing ion

gradient to fund synthesis of ATP Ion gradientH+ gradient across inner

membrane of mitochondrion Chemiosmosiscarrying out cellular work

using energy stored in the form of H+ iongradient across a membrane.


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ATP synthasemultisubunit complex

with four main parts

Each partmultiple polypeptides H+ ions move one by one into binding

sites on one of the parts, resulting in

spinning of the rotor in a way to catalyseATP production


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ETCenergy converter

Makes use of exergonic flow of electrons

to pump H+ into intermembrane space. Protonstendency to flow back

towards the matrix( down its

concentration gradient) The membrane then, offers only one

route or exitATP synthase


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Proton motive forcethe H+ gradient

generated when H+ is pumped into the

intermembrane space. Chemiosmosisan energy coupling

mechanism that uses energy stored inthe form of H+ gradient across amembrane to drive cellular work.


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The Electron Transport Chain