Mitochondrial and bacterial electron transport, oxidation reduction by Akshay Darji

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

4. 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.

5. Flow chart of electron transport chain

6. 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.

7. 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.

8. 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.

9. 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 O 2 . At the end of complex 4 ,net transfer of 4 protons into the intermitochondrial space.

10. 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

11. 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

12. 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.

13. 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.

14. Video clip http://youtu.be/MS6OX5zla_Y

15. I nhibitors 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. Cyanid e, azide , and carbon monoxide bind with complex 4 and inhibits the terminal transfer of electron to oxygen.

16. 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.

17. 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.

18. 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.

19. 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.

20. 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 b 558 , Cyt b 562 , Cyt d, Cyt o).

21. 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.

22. 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.

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

24. 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.

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