The electron transport chain is comprised of a series of enzymatic reactions within the inner membrane of the mitochondria, which are cell organelles that release and store energy for all physiological needs. As electrons are passed through the chain by a series of oxidation-reduction reactions, energy is released, creating a gradient of hydrogen ions, or protons, across the membrane. The proton gradient provides energy to make ATP, which is used in oxidative phosphorylation.

1. ELECTRON
TRANSPORT CHAIN
PREPARED BY; MISS RABIA KHAN BABER

2. AIMS AND OBJECTIVES OF PPT
OXIDATIVE
PHOSPHORYLATION
ELECTRON TRANSPORT
CHAIN
MITOCHONDRIA
STRUCTURE
OVERVIEW
COMPLE
X I
COMPL
EX II
COMPL
EX III
COMPLE
X IV
TOTAL ENERGY
CALCULATION
ATP SYNTHASE
ATP
SYNTHESIS
CHEMIOSMOSIS
ELECTRO CHEMICAL
GRADIENT
BEFORE ELECTRON
TRANSPORT CHAIN

3. OXIDATIVE PHOSPHORYLATION
 Oxidative phosphorylation is the metabolic pathway in which cells
use enzymes to oxidize nutrients, thereby releasing the chemical
energy stored within in order to produce adenosine triphosphate. In
most eukaryotes, this takes place inside mitochondria. Almost all
aerobic organisms carry out oxidative phosphorylation.
In Oxidative phosphorylation ATP is formed as a result of the transfer
of electrons from NADH or FADH 2 to O 2 by a series of electron
carriers.

4. STEPS OF OXIDATIVE
PHOSPHORYLATION
Within the Electron Transport Chain

5. THE ELECTRON TRANSPORT CHAIN
The electron transport chain is comprised of a series of enzymatic
reactions within the inner membrane of the mitochondria, which are
cell organelles that release and store energy for all physiological
needs.
As electrons are passed through the chain by a series of oxidation-
reduction reactions, energy is released, creating a gradient of hydrogen
ions, or protons, across the membrane. The proton gradient provides
energy to make ATP, which is used in oxidative phosphorylation.

6. REACTIONS OF THE ELECTRON
TRANSPORT CHAIN
The reactions of the electron transport chain are carried out by a series
of membrane proteins and organic molecules. They are arranged in
four complexes. In eukaryotes, the electron transport chain is located
in the inner mitochondrial membrane. In prokaryotes, it is located
within the plasma membrane.
Electrons move through the electron transport chain from a higher to
lower energy state. Energy release moves protons through channels in
the membrane proteins, moving them into the inner membrane space.
This leads to a buildup of positively charged protons, which creates an
electrical potential across the membrane.

8. ETC COMPLEXES

9. ELECTRON
TRANSPORT
CHAIN
COMPLEXES
COMPLEX I
NADH Dehydrogenase
Complex
*Also called NADH
Oxidoreductase
*Contains iron,
flevin and sulphur
compounds
COMPLEX II
Succinate
Dehydrogenase
complex
* Contains iron
sulphur clusters
COMPLEX III
Cytochrome
Reductase complex
* Cytochrome is
group of proteins
that contain heme as
their complex
COMPLEX IV
Cytochrome C
Oxidase Complex
*Heme and Copper
containing complex

10. COMPLEX I-THE NADH
DEHYDROGENASE COMPLEX
This complex is also known as NADH dehydrogenase complex, consists of
42 different polypeptides, including FMN containing flavoprotein and at
least six FeS centers.
Complex I is ‘L’ shaped with its one arm in the membrane and another arm
extending towards the matrix.
During catabolic reaction, NAD+ is reduced to NADH+ H+ and this NADH
+ H+ feeds electrons and protons at the point of origin in the ETC.
Both e– and protons are transported to FMN which is then reduced to
FMNH2.

11. FMNH2 transfers only e– to FeS center whereas protons are extruded
outside the membrane (intermembrane space), in the process
FMNH2 is oxidized back to FMN.
Electrons flow through FeS centers which alternate between reduced
(Fe2+) and oxidized (Fe3+) forms.
Electrons are finally transferred to ubiquinone, which along with
protons obtained by the hydrolysis of water in the matrix site of the
membrane is reduced to UQH2.

12. COMPLEX II- SUCCINATE
DEHYDROGENASE
Complex II is also known as succinate dehydrogenase complex.
Succinate dehydrogenase complex is located towards the matrix side of
the membrane.
Succinate is oxidized to fumarate as it transfers two e–s and two protons
to FAD.
FAD is reduced to FADH2.
FAD transfers only electrons through FeS center to quinone.

15. COMPLEX III
CYTOCHROME C OXIDOREDUCTASE
The third complex is composed of cytochrome b, another Fe-S protein,
and cytochrome c proteins.
Cytochrome proteins have a prosthetic group of heme. The heme molecule
is similar to the heme in hemoglobin, but it carries electrons, not oxygen.
As a result, the iron ion at its core is reduced and oxidized as it passes the
electrons, fluctuating between different oxidation states: Fe++ (reduced)
and Fe+++ (oxidized).
Complex III pumps protons through the membrane and passes its electrons
to cytochrome c for transport to the fourth complex of proteins and
enzymes (cytochrome c is the acceptor of electrons from Q; however,
whereas Q carries pairs of electrons, cytochrome c can accept only one at a
time).

16. COMPLEX IV –
CYTOCHROME C OXIDASE
It is also called as cytochrome oxidase.
Cytochrome c undergoes oxidation in the side of the membrane facing the
intermembrane space and O2 is reduced in the matrix side of the membrane
to H2O.
Complex IV consists of iron containing heme-a and heme-a3.
Along with iron atoms, cytochrome oxidase also consists of Cu A and Cu
B.
Cu A is closely but not intimately associated with heme ‘a’ and Cu B is
intimately associated with heme a3.
Electrons from cytochrome c flows to Cu A and then to heme ‘a’ and then
to heme a3 and then to Cu B and then finally to Oxygen.
Cytochrome c —> Cu A —–> Heme a—–> heme a3—->Cu B—> O2

17. The copper atoms interconvert between cuprous (reduced) and cupric
(oxidized).
Electrons from Cu B and heme a3 is transferred to O2.
Two protons are supplied from the matrix side forming OH– and OH–.
Now, addition of two more proton from matrix side resulting in
formation of two molecule of water (2H2O).

18. CHEMIOSMOSIS
In chemiosmosis, the free energy from the series of redox reactions is
used to pump hydrogen ions (protons) across the membrane. The
uneven distribution of H+ ions across the membrane establishes both
concentration and electrical gradients, owing to the hydrogen ions’
positive charge and their aggregation on one side of the membrane.
ELECTROCHEMICAL GRADIENT
An electrochemical gradient is a gradient of electrochemical potential,
usually for an ion that can move across a membrane.

19. SYNTHESIS OF ATPAND
ROLE OF ATP SYNTHASE
Chemiosmotic theory given by Peter Mitchell (1961) in the widely
accepted mechanism of ATP generation.
According to this theory electron and proton channel into the
membrane from the reducing equivalence flows through a series of
electron carriers, electrons flow from NADH through FMN, Q,
cytochrome and finally to O2.
However, proton as they flow through the membrane are extended at
different position in the intermembrane space.
The extension of protons creates a slight positivity/acidity to the
outerside of membrane.
Reduction of quinones and O2 to water requires protons which are
provided by the hydrolysis of water in the matrix side of the
membrane.

20. This results in accumulation of hydroxyl ion in the inner (matrix) side
of membrane resulting in slight negativity/alkalinity in the inner side
of the membrane.
This creates a charge difference between outer side of the membrane,
and inner side of membrane which energizes the membrane.
This is electrochemical potential, and this potential along with the pH
gradient generates the proton motive force (PMF).
This proton motive force tends to drive the proteins through ATP
synthase in to the inner side of the membrane, the consequence of
which is ATP production.

21. ENERGY CALCULATIONS OF THE ETC
GLYCOLYSIS GLUCOSE ----PYRUVATE 2 ATPS
2 NADH2
7 ATP
KREB’S CYCLE WHEN GLUCOSE PASSES
THROUGH ONE CYCLE
2 GTPS
6 NADH
2 FADH2
20 ATP
ELECTRON TRANSPORT
CHAIN
GLUCOSE --- PYRUVATE
PYRUVATE---- ACETYL CO A
KREB’S CYCLE
2 NADH
2 NADH
6 NADH
2 FADH2
5 ATPS
5 ATPS
15 ATP
3 ATP
1 NADH CAN PUMP 10 HYDROGEN IONS WHICH CAN PHOSPHORYLATE 1 ADP MOLECULE
1 FADH2 CAN PUMP 6 HYDROGEN IONS
IN TOTAL WE HAVE 32 ATPS PER MOLECULE OF GLUCOSE WHICH PASSES THROUGH ALL THESE
BIOCHEMICAL REACTIONS

22. SUMMARY
 The electron transport chain is the portion of aerobic respiration that uses
free oxygen as the final electron acceptor of the electrons removed from the
intermediate compounds in glucose catabolism.
The electron transport chain is composed of four large, multiprotein
complexes embedded in the inner mitochondrial membrane and two small
diffusible electron carriers shuttling electrons between them.
The electrons are passed through a series of redox reactions, with a small
amount of free energy used at three points to transport hydrogen ions
across a membrane.

23. This process contributes to the gradient used in chemiosmosis.
The electrons passing through the electron transport chain gradually
lose energy, High-energy electrons donated to the chain by either
NADH or FADH2 complete the chain, as low-energy electrons reduce
oxygen molecules and form water.
The level of free energy of the electrons drops from about 60 kcal/mol
in NADH or 45 kcal/mol in FADH2 to about 0 kcal/mol in water. The
end products of the electron transport chain are water and ATP. A
number of intermediate compounds of the citric acid cycle can be
diverted into the anabolism of other biochemical molecules, such as
nonessential amino acids, sugars, and lipids. These same molecules can
serve as energy sources for the glucose pathways.

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