NADH and FADH formed in glycolysis and TCA cycle are utilized in electron transport chain and ATP id generated by oxidative phosphorylation.

1. ELECTRON TRANSPORT
CHAIN & OXIDATIVE
PHOSPHORYLATION
PRESENTED BY; ISMA ZULFIQAR

2. OVERVIEW
• Electron transport and oxidative phosphorylation re-oxidize NADH and
FADH2 and trap the energy released as ATP.
• In eukaryotes, electron transport and oxidative phosphorylation occur
in the inner membrane of mitochondria whereas in prokaryotes the
process occurs in the plasma membrane.

3. Biochemical
anatomy of a
mitochondrion

4. ELECTRON TRANSPORT CHAIN
• This is the final common pathway in aerobic cells by which
electrons derived from various substrates are transferred to
oxygen. Electron transport chain (ETC) is a series of highly
organized oxidation-reduction enzymes.
• The inner membrane transport only specific substances such as
ATP, ADP, pyruvate, succinate, α-ketoglutarate, malate and
citrate etc. The enzymes of the electron transport chain are
embedded in the inner membrane in association with the
enzymes of oxidative phosphorylation.

5. COMPLEX OR COMPONENTS OF ETC
• The electron transport chain in the mitochondrial membrane
has been separated in 4 (four) complexes from Complex I-IV.
• Complex I, also called NADH ubiquinone oxidoreductase or
NADH dehydrogenase, is a large enzyme composed of 42
different polypeptide chains. High-resolution electron
microscopy shows Complex I to be L-shaped, with one arm of
the L in the membrane and the other extending into the matrix.

6. COMPLEX I, OF
ELECTRON
TRANSPORT
CHAIN

7. COMPLEX II
Succinate to ubiquinone
• It is smaller and simpler than
Complex I.
• Flow of electrons from succinate to
CoQ occurs via FADH2
• It does not pump protons across the
mitochondrial membrane, hence this
protein complex does not contribute
to proton gradient that lead to ATP
production.

8. COMPLEX III
UBIQUINONE TO CYTOCHROME C
• The transfer of electrons from
ubiquinol (QH2) to
cytochrome c.
• Functions as
i. Proton pump, and
ii. Catalyze transfer of electrons
It is believed that 4 (four)
protons are pumped across the
mitochondrial membrane
during the oxidation.

9. COMPLEX IV
CYTOCHROME C TO O2
• Complex IV, also called
cytochrome oxidase, carries
electrons from cytochrome c to
molecular oxygen, reducing it to
H2O.
• This is the terminal component of
ETC. It catalyses the transfer of
electrons from Cyt-c to molecular
O2 via Cyt-a, Cu++ ions and Cyt-
a3.

10. Summary of the flow of electrons and protons
through the four complexes of the respiratory
chain

12. PROTON-MOTIVE FORCE
• For each pair of electrons transferred to O2, four protons are
pumped out by Complex I, four by Complex III, and two by Complex
IV. This introduces proton motive force.
• The proton-motive force, has two components:
I. The chemical potential energy due to the difference in
concentration of a chemical species (H) in the two regions
separated by the membrane.
II. The electrical potential energy that results from the separation of
charge when a proton moves across the membrane.

13. OXIDATIVE PHOSPHORYLATION
• The chemiosmotic model, proposed by Peter Mitchell, is the
paradigm for this mechanism.
• According to chemiosmotic theory applied to mitochondria, electrons
from NADH and other oxidizable substrates pass through a chain of
carriers arranged asymmetrically in the inner membrane. Electron
flow is accompanied by proton transfer across the membrane,
producing both a chemical gradient and an electrical gradient.
• The inner mitochondrial membrane is impermeable to protons,
protons can reenter the matrix only through proton-specific
channels. The proton-motive force that drives protons back into the
matrix provides the energy for ATP synthesis.

15. What would happen to the energy stored in the proton
gradient if not used to synthesize ATP or other cellular work?
• It would be released as heat, and interestingly enough, some types of cells
deliberately use the proton gradient for heat generation rather than ATP
synthesis. This might seem wasteful, but it's an important strategy for
animals that need to keep warm.
• Hibernating mammals (such as bears) have specialized cells known as brown
fat cells. In the brown fat cells, uncoupling proteins are produced and
inserted into the inner mitochondrial membrane. These proteins are simply
channels that allow protons to pass from the intermembrane space to the
matrix without traveling through ATP synthase. By providing an alternate
route for protons to flow back into the matrix, the uncoupling proteins allow
the energy of the gradient to be dissipated as heat.

16. ATP YIELD
• Oxidative
phosphorylation
produces most
of the ATP
made in aerobic
cells. Complete
oxidation of a
molecule of
glucose to CO2
yields 30 or 32
ATP.

17. REFERENCES
• https://www.khanacademy.org/science/ap-biology/cellular
energetics/cellular-respiration-ap/a/oxidative-
phosphorylation-etc
• Lehninger Principles of Biochemistry, 6th edition.
• Instant Notes in Biochemistry, 4th eidition.
• Textbook of medical biochemistry by MN chatterjea, 8th edition.