basic of ETC

1. Mitochondrial and bacterial electron
transport.
Guided by :- Dr. C.D. Afuwale
Darji Akshay k. (05)
M.sc. Sem – 3
DEPARTMENT OF MICROBIOLOGY

2. outline
• Introduction
• What is mitochondria ?
• What is ETC ?
• Mitochondrial electron transport
• Bacterial electron transport

3. What is Mitochondria?
• Mitochondria are small granular or filamentous bodies
which are present in the cytoplasm of eukaryotic cell and
also known as the “powerhouse of the cell”
FUNCTION
• it is a site of ATP synthesis for the cell.
• Regulates the metabolic activity of the cell.
• Promotes the growth of new cell & cell multiplication.
• Plays important role in apoptosis or programmed cell
death

5. What is ETC ?
• The electron transport chain (ETC) is a series of
complexes that transfer electron from electron
donors to electron acceptors via redox reaction and
couples this transfer with transfer of protons across
a membrane.
• ETC, is a chain of reaction that converts redox
energy available from oxidation of NADH and
FADH2, into Pmf which is used to synthesize ATP
through confirmation changes in the ATP syntheses
complex through a process called oxidative
phosphorylation.

6. Flow chart of electron transport chain

8. Complex 1
• Complex 1- NADH Dehydrogenase
• Large multisubunit complex with about 40 polypeptide
chains.
• PROSTHETIC GROUPS:
FMN
Fe-s center( at least six)
• NADH that is formed will enter at complex 1
• After the transfer of electrons from complex 1 to
coenzyme Q there is a net transfer of 4 protons to the
intermembrane space.

9. Complex 2
• Also called as succinate dehydrogenase
• Entry gate for FADH
• Succinate dehydrogenase ( from the citric acid
cycle) directs transfer of electrons from
succinate to CoQ via FADH2
• Acyl-CoA dehydrogenase (from oxidation of fatty
acids) also transfers electrons to CoQ via
FADH2.
• No transfer of protons from matrix to the
intermembrane space.

10. Complex 3
• Complex 3 ( cytochromes bc1)
• Electron transfer from ubiquinol to cytochrom c.
• At the end of complex 3 net transfer of 4
protons into the intermembrane space.
• Complex 3 functions as proton pump.

11. Complex 4
• Combination of cytochromes a and a3
• 10 protein subunits
• 2 types of prosthetic groups:
2 heme and 3 Cu ion
• Electrons are delivered from cytochromes a and
a3 to O2.
• At the end of complex 4 ,net transfer of 4
protons into the intermitochondrial space.

12. Complex 5
• Also called as ATP synthase
• Made up of F0 and F1 complexes
• F1 -9 subunits
• F0- 3 subunits
• The F0 subcomplex is composed of channel
protein ‘C’ subunit to which F1 synthase is
attached

13. Coenzyme Q
• Also known as ubiquinone
• Is a benzoquinone liked to a number of isoprene
units
• Q refers to the quinone chemical group
• It is the only electron carrier in the electron
transport chain that is not a protein bound
prosthetic group
• Fully oxidized – ubiquinone Q
• Fully reduced – ubiquinol QH2

14. Mitochondrial electron transfer
• The mitochondrial electron transport chain is
composed of three main membrane-associated
electron carriers flavoproteins (FMN,FAD),
cytochromes and quinones
• MET system is arranged into four enzyme
complexes of carriers, each capable of
transporting electron part of the way to O2.

15. • Coenzyme Q and cytochrome c connect the
complexes with each other.
• The four enzyme complexes are NADH-Q
oxidoreductase, succinate-Q reductase, Q-
cytochrome c oxidoreductase and cytochrome c
oxidase.
• These complxes are each of them consisting of
diff. prosthetic group.

17. • Video clip
• http://youtu.be/MS6OX5zla_Y

18. Inhibitors of electron transport
• Rotebine :- Inhibits transfer of electron through
complex 1.
• Amobacterial :- Inhibits electron transport
through complex 1.
• Antimycin :- Blocks electron transport at the
level of the complex 3.
• Cyanide, azide, and carbon monoxide bind with
complex 4 and inhibits the terminal transfer of
electron to oxygen.

19. Oxidative phosphorylation
• It is a metabolic pathway in which cells use enzymes
to oxidize nutrients, thereby releasing the chemical
energy stored with in order to produce ATP.
• As the electrons are transferred , some electron
energy is lost with each transfer.
• This energy is used to pump protons (H+) across the
membrane from the matrix to the innermembrane.
• A proton gradient is established.

20. • The higher negative charge in the matrix attracts the
protons (H+) back from the intermembrane space to
the matrix.
• The accumulation of protons in the intermembrane
space drive protons into the matrix via diffusion.
• Most protons move back to the matrix through
ATPsynthase.
• ATP synthase uses the energy of the proton gradient
to synthesize ATP from ADP + Pi.

22. Bacterial electron transport
• The electron transport chains of bacteria
(prokaryotes) operate in plasma membrane
(mitochondria are absent in prokaryotes). Some
bacterial electron transport chains resemble the
mitochondrial electron transport chain.
Paracoccus denitrificans is a gram-negative,
facultative anaerobic soil bacterium.
• It is a model prokaryote for studies of respiration.
When this bacterium grows aerobically, its
electron transport chain possesses four complexes
that correspond to the mitochondrial chain.

23. • bacterial electron transport chains vary in their
electron carriers (e.g., in their cytochromes) and are
usually extensively branched. Electrons often enter
at several points and leave through several terminal
oxidases. Bacterial electron transport chains are
usually shorter and possess lower phosphorus to
oxygen (P/O) ratios than mitochondrial transport
chain.
• Thus bacterial (prokaryotic) and mitochondrial
(eukaryotic) electron transport chains differ in
details of construction although they operate
employing the same fundamental principles.

24. • Although the electron transport chain of E. coli
transports electrons from NADH (NADH is the
electron donor) to acceptors and moves protons
(H+) across the plasma membrane similar to
mitochondrial electron transport chain, it is quite
different from the latter in its construction E. coli
transport chain is short, consists of two branches
(cytochrome d branch and cytochrome o
branch), and a quite different array of
cytochromes (e.g., Cyt b558, Cyt b562, Cyt d, Cyt o).

25. • Coenzyme Q (ubiquinone) carries electrons and
donates them to both branches, but the branches
operate under different growth conditions. The
cytochrome d branch shows very high affinity for
oxygen and operates at low oxygen levels (low
aeration) usually when the bacterium is in
stationary phase of growth.

26. • This branch is not as efficient as the cytochrome o
branch because it does not actively pump protons
to periplasmic space.
• The cytochrome o branch shows moderately high
efficiency for oxygen and operates at high oxygen
concentrations (high aeration). This branch
operates normally when the bacterium is in log
phase of its growth (i.e., growing rapidly), and
actively pumps protons (H+) in the periplasmic
space.

28. • NADH:- Nicotinamide Adenine Dinulceotide – H
• FAD:- Flavin Adenine Dinulecotide
• FMN:- Flavin Mononucleotide
• ETC:- Electron Transport Chain
• MET:- Mitochondrial Electron Transport chain
• cyt. :- Cytochrome

29. • Oxidative phosphorylation :- Process of ATP
formation when electrons are transferred by
electron carrier from NADH or FADH2 to O2.
• Glycolysis :- Metabolic pathway that converts
glucose mol. To pyruvate constitute.
• Prosthatic group :- A tightly bound nonpolypeptide
structure required for activity of an enzyme or othar
protein, for ex. The haem of haemoglobin
• Periplasmic space :- Space between cell membrane
and cell wall.

30. Reference
• Nelson D.L.,Cox M.M., Lehninger Principles of
Biochemistry, 6th edition, New york, worth publisher
(2013), ch.-19, page 732-746.
• https://www.biologydiscussion.com/bacteria/electron-
transport-chain-of-bacteria-with-diagram/55269