Biological oxidation and reduction

Loss of electrons by an atom, ions or molecule during a chemical reaction & increase its oxidation state.
Gain of electrons by an atom , ion or molecule during a chemical reaction & decrease in its oxidation state
The reactions which involves both reduction process & complementary oxidation process called redox reaction.

1. Biological oxidation and reduction BY; WISHAL BUTT

2. OXIDATION Loss of electrons by an atom, ions or molecule during a chemical reaction & increase its oxidation state.

3. REDUCTION Gain of electrons by an atom , ion or molecule during a chemical reaction & decrease in its oxidation state

4. REDOX REACTIONS The reactions which involves both reduction process & complementary oxidation process called redox reaction.

5. EXPLANATION Transfer of phosphoryl group Electron transfer ( redox ) Flow of e ⁻ is responsible for all work done by the organism In nonphotosynthetic organisms source of electrons is food In photosynthetic organism initial e⁻ donor is a chemical specie excited by absorption of light. Metabolic pathway is complex Electrons metabolic intermediates e⁻ carrier acceptor having high e⁻ affinity with release of energy

6. HALF REACTIONS Reaction; Fe ⁺ᴵᴵ + Cu⁺ᴵᴵ Fe⁺ᴵᴵᴵ + Cu⁺ Two half reactions ; Fe⁺ᴵᴵ Fe⁺ᴵᴵᴵ + e⁻ Cu⁺ᴵᴵ + e⁻ Cu⁺ Fe⁺ᴵᴵ & Fe⁺ᴵᴵᴵ Reductant – oxidant pair e⁻ donor e⁻ + e⁻ acceptor Fe⁺ᴵᴵ is electron donor Fe⁺ᴵᴵᴵ is electron acceptor

7. Example: oxidation of reducing sugar: RCHO + 4OH ⁻ 2 Cu⁺ᴵᴵ RCOOH + Cu₂O + H₂O

8. Oxidation involve dehydroogenation Alkane to alkene: C ₂ H ₄ - CH= CH- oxidation takes place due to the loss of hydrogen atom.

9. Electron transfer ways Directly as electrons As hydrogen atom As hydride ion Direct combination with oxygen

10. Electron transport chain Glucose metabolize & give CO ₂ plus H₂O. NAD⁺ & FAD are converted to NADH & FADH₂ Down the chain energy decreases

11. mitochondrion ETC is present in the inner mitochondrial membrane. electron trans port and ATP synthesis occurs continuously in all cells having mitochondria.

12. Structure; Inner membrane Impermeable ATP, ADP , pyruvate Carriers Rich in proteins used in electron transport & oxidative Phosphorylation . cristae

13. 2. Atp synthase complex * Protein complexes reffered as inner membrane particles. * Attached on inner surface Appear as sphere 3. MATRIX; * Gel like soln. 50% protein * Enzymes for oxidation of pyruvate , aa, fatty acids, & carboxylic acid cycle. * Urea & heme * NAD ⁺, FAD, ADP, Pi

14. Organization of chain

15. Reactions of etc All members are proteins except coenzyme Q. Works as enzyme e.g. dehyrogenase Iron as iron sulfur center, Prophyrin ring as in cytochromes contain copper as in cytochrome a +a ₃ complex.

16. Formation of nadh NAD ⁺ reduce to NADH by Dehydrogenases that remove two H- atoms from substrate hydride ion transform NAD⁺ to NADH & a free proton H⁺

17. 2. Nadh dehydrogenase * H ⁺ & hydride ion carried by NADH transfer to NADH dehydrogenase, an enzyme complex ( complex 1). * complex-1 has FMN accepts two H⁺ & changes into FMNH₂. * NADH dehydrogenase has Fe-atoms paired with S-atoms in Fe-S center necessary to transfer H-atom to next member.

18. 3.Coenzyme q; * Quinone derivative, having long isoprenoid tail, called ubiquinone because it is ubiquitous in biological system. * accept H-atom both from FADH ₂ & FMNH₂.

19. 4.CYTOCHROMES; * Remaining members of ETC are cytochromes . * Having heme group made up of prophyrin ring containing an iron atom. * reversibly converted from its ferric to ferrous form. Is its function. * Electrons passed along the chain from coenzyme Q cytochrome b & c cytochrome a + a ₃ .

20. 5. Cytochrome a + a ₃; * Only electron carrier in which heme iron has free ligand , react directly with molecular oxygen. * here transported e ⁻, molecular oxygen, & free protOn are brought togather to produce H₂O.

21. 6. Site-specific inhibitors;

22. Energy release; * Energy releases when e ⁻ moves along the ETC, from e⁻-donor, to e⁻-acceptor. 1.REDOX PAIR; oxidation of one comp. is always compensated b y reduction of second one. e.g. NADH NAD⁺ accoumpained by FAD FADH₂

23. 2. Standard reduction potentials; The standard reduction potential is the tendency for a chemical species to be reduced, and is measured in volts at standard conditions. The more positive the potential is the more likely it will be reduced. For redox pairs it is listed from more –ve E ₀ +ve E₀. More –ve the value , greater tendency of reductant to give e⁻. More +ve the value , greater tendency of oxidant to accept e⁻.

24. 3. Δ g & Δ e₀; Δ G = -nF Δ E₀ Change in free energy is directly related to the magnitude of the change in E ₀. n = no. of electron transferred. F = Faradays constant. Δ E₀ = E₀ of electron accepting pair - E₀ of electron donating pairs. Δ G = change in standard free energy.

25. References;