1. Dr.S.Chakravarty, MD

2. Oxidation is defined as the removal of electrons and reduction as the gain of electrons. Oxidation is always accompanied by reduction of an electron acceptor.

3. Oxidation : Reduction : Oxidation and reduction: Loss of electrons Loss of hydrogen Gain of oxygen Gain of electrons Gain of hydrogen Loss of oxygen

4. REDOX POTENTIAL When a substance exists both in the reduced state and the oxidised state, the pair is called a REDOX COUPLE. The redox potential of this couple is estimated by measuring the EMF of a sample half cell connected to a standard half-cell.

5. 1M H + ~ H gas @ 1 Atmpspheric pressure E 0 ’ = 0 meV Salt bridge

6. WHEN A SUBSTANCE HAS LOWER AFFINITY FOR ELECTRONS THAN HYDROGEN IT HAS A NEGATIVE REDOX POTENTIAL LOWER AFFINITY FOR ELECTRONS = NEG. REDOX POTENTIAL = STRONG REDUCING AGENT AND VICE VERSA. ELECTRONS MOVE ALWAYS FROM MORE ELECTRONEGATIVE TO ELECTROPOSITIVE LOSS OF FREE ENERGY (THIS ALWAYS ENSURES THAT FREE ENERGY DECREASES)

7. 0 2  H 2 O FOOD (REDUCED ) SMALLER MOLECULES REDUCED COENZYMES e.g NAD ENERGY BIOLOGIOCAL OXIDATIONBIOLOGIOCAL OXIDATION e- ELECTRON TRANSPORT CHAIN MITOCHONDRION

8. Redox Potentials OxidantReductant E 0 ’ ( in V) NAD + NADH + H + -0.32 Cytochrome b +++ Cytochrome b ++ +0.07 Co-eneyme QCo-eneyme QH 2 +.010 Cytochrome c +++ Cytochrome c ++ +0.22 Cytochrome a +++ +0.29 ½ O 2 +2HH2OH2O+.82

9. ½ O 2 + 2H +  H 2 O ( E 0 ’ = +0.82 ) NAD + + H +  NADH ( E 0 ’ = -0.32)  E 0 ’ = +0.82 – (-0.32 ) = 1.14 COMBINE BOTH OF THESE :- ½ O 2 + NADH + H +  H 2 O + NAD + Δ G 0 = -nFΔE 0 = - 2 x 23.06 x 1.14 = -52.6 kcal/mol

10. Harper’s Illustrated Biochemistry

11. With the help of successive reductions in the electron transport chain assembly, this energy change is released in small increments so that the body can utilize it.

12. HIGH ENERGY COMPOUNDS THESE COMPOUNDS WHEN HYDROLYSED RELEASE A LARGE AMOUNT OF ENERGY INDICATED BY SQUIGGLE (~) FREE ENERGY VARIES FROM -7 TO -15 kcal/mol

14. Defn :- When the energy of high energy compound is directly transferred to nucleoside diphosphate to form a triphosphate without the help from electron transport chain. Examples :- 1.Bisphosphoglycerate kinase ( Glycolysis) (1,3 bisphosphoglycerate  3-phosphoglycerate) 2. Pyruvate kinase (Glycolysis) (Phosphoenol pyruvate  Pyruvate) 3. Succinate thiokinase (TCA cycle) (Succinyl CoA  Succinate )

15. Biological Oxidation and Oxidative Phosphorylation Biological Oxidation :- The transfer of electrons from the reduced co-enzymes though the respiratory chain to oxygen is known as biological oxidation. Energy released during this process is trapped as ATP. This coupling of oxidation with phosphorylation is called as OXIDATIVE PHOSPHORYLATION.

16. Impermeable to ions and most other compounds The mitochondrion contained the enzymes responsible for electron transport and oxidative phosphorylation USMLE concept!

17. Harper’s Illustrated Biochemistry

18. IMPORTANT MITOCHONDRIAL TRANSPORTERS Pyruvate HydrogenMalate Citrate ADPATP INNER MITOCHONDRIAL MEMBRANE

20. Malate –Aspartate shuttle Operates in Liver, Kidney and Heart

21. Glycerol -3 –phosphate shuttle Operates mainly in muscle and Brain.

22. The flow of electrons occurs through successive dehydrogenase enzymes in mitochondria, together known as the electron transport chain (ETC). (the electrons are transferred from lower to higher redox potential)

24. Protein complexes: NADH-CoQ Dehydrogenase (Complex I) Succinate-CoQ Dehydrogenase (Complex II) CoQ-cytochrome c Reductase (Complex III) Cytochrome c Oxidase (Complex IV) Mobile complexes: 1.Co-enzyme Q or ubiquinone 2.Cyt C

25. COMPLEX I FMN-FeS Complex III FeS-Cytb-Cyt c1 Co Q Complex IV Cyt a-a3 (Fe+3,Cu+2) Cyt C COMPLEX II FeS 8.Succinate DH(TCA CYCLE) 9. Acyl Coa A DH(fatty acid oxidn.) 10. Glycerol 3-P DH(mitochondrial) FAD Mitochondrial Matrix NAD 1. Glyceraldehyde - 3P 2.Isocitrate 3.Malate 4.Glutamate 5.β-OH-acyl CoA 2H + H2OH2O + SITE 1 4 PROTONS PUMPED OUT SITE 2 4 PROTONS PUMPED OUT SITE 3 2 PROTONS PUMPED OUT Fp(FAD)  lipoate  6.Pyruvate 7.α-ketoglurarate Inner mitochondrial membrane

26. Pathways for flow of electrons: For NADH: Complex 1 -> complex 3 -> complex 4 For FADH2: (more positive redox) Complex 2 -> complex 3 -> complex 4 NAD + or FAD There are 2 sites of entry for electrons into the electron transport chain: Using either Both are coenzymes for dehydrogenase enzymes

27. 1 2 34

28. COENZYME Q The ubiquinone is reduced successively to semiquinone (QH) and finally to quinol (QH2)  It accepts a pair of electrons from NADH or FADH2 through complex I or complex II respectively.  Co-enzyme Q is a quinone derivative having long isoprenoid tail.  2 molecules of cytochrome c are reduced.  The Q cycle thus facilitates the switching from the 2 electron carrier ubiquinol to the single electron carrier cytochrome c.  This is a mobile carrier.

29. The transport of electrons from inside to outside of inner mitochondrial membrane is accompanied by the generation of a proton gradient across the membrane. Protons accumulate outside the membrane creating an electrochemical potential. This drives the synthesis of ATP by ATP synthase.

30. Harper’s Illustrated Biochemistry

32. The pH outside is 1.4 units lower than inside. The outside is positive 0.14V relative to inside. The proton motive force (PMF ) IS 0.224 v corresponding to a free energy change of 5.2 kcal/mol of protons.

33. ENERGETICS OF ATP SYNTHESIS – ENERGY RELEASED = 52kcal/mol – Synthesis of 1ATP and Pi requires 7.3 kcal/Mol molecules – Chemical energy trapped = 7.3 x 3 = 21.9kcal = 40% – Rest 60% energy is dissipated as HEAT !!

35. F0 – F1 complex : Fo complex: – O STANDS FOR OLIGOMYCIN Made of 12 subunits. H+ passes through each subunit from membrane space to inner space rotating the Fo complex (turbines).

36. F1 complex:Has 9 polypeptide chains,(3 alpha, 3 beta, 1 gamma, 1 sigma, 1 epsilon) the α chains have binding sites for ATP and ADP and beta chains have catalytic activity. ATP SYNTHESIS NEEDS Mg +2 IONS ADP and Pi bind the alpha subunit Binding change mechanism - conformation change of beta subunits causes release of ATPs from the complex. ATPs formed in the mitochondrial matrix are translocated to cytosol by ATP/ADP translocase

37. 1 ) ADENINE NUCLEOTIDE TRANSPORTER 2)H + /P i SYMPORT

38. According to recent estimates, NADH may generate only 2.5 ATPs while FADH 2 may generate only 1.5 ATP. So, instead of 38 ATP, only 32 ATPs are generated from glucose.

39. ATP IS THE ENERGY CURRENCY