Electron transport chain(ETC)

IntroductionDiscovery

In 1961, an American biochemist, Albert

Lehninger, discovered that the citric acid cycle

and the electron-transfer chain of enzymes (where

1 NADH makes 3 ATPs) are located within each

cell’s mitochondria.

And each cell has many mitochondrion power

plants that produce an energy output which can

be measured.

Importance and Location

•Importance:

These are the mechanism by which

NADH plus H+ and FADH2 are used to

generate ATP

•Location:

Inner mitochondrial membrane

(showing my mammalian bias)

ETC

The majority of the energy conserved during

catabolism reactions occurs near the end of the

metabolic series of reactions in the electron

transport chain.

The electron transport or respiratory chain

gets its name from the fact electrons are

transported to meet up with oxygen from

respiration at the end of the chain.

The overall electron chain transport reaction is:

2 H+ + 2 e+ + 1/2 O2 ---> H2O + energy

ETC

Notice that 2 hydrogen ions, 2 electrons,

and an oxygen molecule react to form as a

product water with energy released in an

exothermic reaction.

This relatively straight forward reaction

actually requires eight or more steps. The

energy released is coupled with the

formation of three ATP molecules per every

use of the electron transport chain

ETC

The Electron transport system contains mainly six components arranged in the following sequence

1.NAD (Nicotinamide adino dehydragenase)

2.FAD ( Flavo adino dehydragenase)

3.cytochrome B

4.cytochrome C

5.cytochrome A and

6.cytochrome A3

Initiation of Electron Transport Chain:

Once the NADH has been made from a

metabolite in the citric acid cycle inside of the

mitochondria, it interacts with the first complex 1

enzyme, known as NADH reductase.

This complex 1 contains a coenzyme flavin

mononucleotide (FMN) which is similar to FAD.

The sequence of events is that the NADH, plus

another hydrogen ion enter the enzyme complex

and pass along the 2 hydrogen ions, ultimately to

an interspace in the mitochondria.

These hydrogen ions, acting as a pump, are

utilized by ATP synthetase to produce an

ATP for every two hydrogen ions produced.

Three complexes (1, 3, 4) act in this

manner to produce 2 hydrogen ions each,

and thus will produce 3 ATP for every use

of the complete electron transport chain.

Oxidation of FAD & NADH

occurs by the following steps

Step1:

The initiation of electron transport system is

the removal of hydrogen from the substrate

by enzyme dehydrogenase

2H 2H+ + 2e-

the hydrogen atom becomes ionized into

protons+ and electrons-

Step2:

The hydrogen ion reduces the co-enzyme NAD

NAD + 2H+ NADH +H+

Step3:

NADH is oxidized into NAD by transferring its

hydrogen ion to FAD which act as the hydrogen

carrier.

Step4:

From FAD each hydrogen ion is discharged in

the cell fluid and electrons are passed on the

cytochromes B,C,A and A3

Step5:

From the cytochromes the electrons are

given to the enzyme cytochrome oxidase.

Step6:

The cytochrome oxidase finally discharge

electron to oxygen.This oxygen units with

hydrogen ions forming water.

Global ETC With ATP

Global ETC With ATP

Site 1NADH + H

NAD

FMN FeS1 FeS2 FeS3 FeS4 FeSn Q b562 b566 FeS cyt c1 cyt c

FAD

FeS

FADH2 FAD

Site 2

Site 3 Site 4

cyt a cyt a3

1/2 O2

H2O

ADP + Pi ATP ADP + Pi ATP ADP + Pi ATP

Step 1: Proton gradient is built up as a result of NADH (produced from oxidation

reactions) feeding electrons into electron transport system.

Step 2: Protons (indicated by + charge) enter back into the mitochondrial matrix

through channels in ATP synthase enzyme complex. This entry is coupled to ATP

synthesis from ADP and phosphate (Pi)

Step 3: The cytochrome oxidase finally discharges electron to oxygen. This

oxygen units with hydrogen ions forming water

Conclusion

1. Protons are translocated across the membrane, from the

matrix to the intermembrane space

2. Electrons are transported along the membrane, through a

series of protein carriers

3. Oxygen is the terminal electron acceptor, combining

with electrons and H+ ions to produce water

4. As NADH delivers more H+ and electrons into the ETS,

the proton gradient increases, with H+ building up

outside the inner mitochondrial membrane, and OH-

inside the membrane.

THANK YOU

Presentation by

R.Vijayarangan