BIOENERGITICS

1. BIO-ENERGITICS M.Prasad Naidu MSc Medical Biochemistry, Ph.D.Research Scholar

2. Bio-energitics • Bio-energitics is the study of energy changes [ release or utilization ] in biochemical reactions. • Reactions where energy is released are called exergonic reactions. • Reactions where energy is utilized are called endergonic reactions.

3. BIO-ENERGITICS • Free energy [G] • Gibb's change in free energy [ G] negative positive zero • Standard free energy [ Go] • Enthalpy [ H] • Entropy [ S]

4. Bio-energitics • Free energy [G]denotes the fraction total energy in the system available to do the work . • Gibbs change in free energy [ G] It is the portion of free energy that is useful to do the work. • Standard free energy change [ G0 ] is the free energy change under standard conditions [ pH 7 and 1M\ L concentration]

5. Bio-Energitics Gibbs Change in free energy [ G ] predicts whether a reaction is favorable or not and the energy available to do work. 1. exergonic reactions ; negative 2.endergonic reactions ; positive 3.equilibrium reactions ; zero

6. BIO-ENERGITICS Enthalpy [H] is the measure of the change in the heat content of the system i.e. energy released or absorbed. Entropy [S] It is the fraction of enthalpy that is not available to do the work. it denotes the randomness of the products and reactants.

7. BIO- ENERGITICS • A biochemical reaction depends on the change in free energy , Enthalpy , and Entropy. G = H - T S [T= absolute temperature in Kelvin]

8. ATP • ATP is the energy currency of the cell • ATP on hydrolysis yields -7.3 Kcal ATP ADP + Pi - 7.3 Kcal • ATP is utilized for Active transport Nerve conduction Muscle contraction synthetic reactions

9. High energy phosphates 1.Pyro-phosphates -------------- ATP 2.Acyl phosphates -------------- 1,3-BPG 3.Enol phosphates -------------- PEP 4.phosphoguanides ------------- creatine –P 5.Thio - esters ------------- Acyl-co A the high energy bond in these compounds is called as Acid –anhydride bond

10. High energy compounds • phopho enol pyruvate [-14.8Kcal] • phospho creatine • 1,3-BPG • SAM • ATP - 7.3Kcal • ADP • G-1-P • F-6-P • G-6-P [-3.3Kcal]

11. Redox pairs • The electrons flow uni directionally from one carrier to the other in ETC. • The carriers are reduced when they accept the electrons and get oxidized when they donate to the other carrier. • the reduced and oxidized forms of the same carrier are referred as redox pairs. • Redox potential is the tendency of the redox pair to donate or accept electrons. • electrons always flow from negative to positive redox potential.

12. Redox pairs REDOX PAIRSREDOX POTENTIAL • NADH\NAD -0.32 • FADH\FAD -0.12 • H2O\O2 +0.82 The ETC is arranged in the increasing order of their redox potentials.

13. Enzymes of biological oxidation • All the enzymes of biological oxidation belongs to the major class of oxido-reductases. They are classified as follows 1.Oxidases 2.Oxygenases 3.Hydroperoxidases 4.dehydrogenases

14. Class Oxido reductases: • Oxidases Eg: Cytochrome oxidase • Oxygenases • Mono-oxygenases Eg: Cyt P450 • Dioxygenases Eg: Tryptophan dioxygenases • Hydroperoxidases • Peroxidases Eg: Glutathione peroxidase • Catalases • Dehydrogenases • Aerobic Eg: Xanthine oxidase • Anaerobic: • NAD linked • FAD linked • FMN linked Enzymes in biological oxidation

15. Enzymes 1.Oxidases ; these enzymes catalyze the removal of hydrogen from the substrates. Oxygen acts as acceptor of hydrogen forming water. E.g. cytochrome -oxidase ,MAO A H2 +1\2 O2 ---------- A + H2O

16. Enzymes 2.Oxygenases • Mono-oxygenases [ mixed function oxidase] incorporates one oxygen atom into the substrate other is reduced to water. E.g. cyt-P450 ,tyrosine hydroxylase etc. A-H + O2 + BH2 AOH + H2O +B 2. di-oxygenases incorporate both oxygen atoms into the substrate. E.g. Tryptophan dioxygenase A H + O2 AOOH

17. Enzymes 3. Hydroperoxidases act on H2O2. 1. peroxidase ; glutathione peroxidase AH2 +H2O2 ---------2H2O + A 2.catalase; 2H2O2 ----------------2H2O +O2

18. ENZYMES 4.Dehydrogenases Catalyze the removal of hydrogen from the substrate. Based on the type of H2 acceptor they are classified as follows 1. aerobic dehydrogenases oxygen is the acceptor of hydrogen. 2. anaerobic dehydrogenases coenzymes act as acceptors of hydrogen NAD+ linked dehydrogenases NADP+ linked dehydrogenases FAD- linked dehydrogenases

19. Enzymes • Aerobic dehydrogenases These are flavoproteins and the product formed is mostly hydrogen peroxide AH2 + O2 -------------A + H2O2 E.g. xanthine oxidase, glucose oxidase etc

20. Enzymes • Anaerobic dehydrogenases hydrogen acceptor s are co-enzymes. When the substrate is oxidized the co-enzyme is reduced AH2 + B ----------------A + BH2

21. Electron transport chain Transport of electrons from reduced substrates to O2 is called as ETC. Site: Inner mitochondrial membrane Components: 1.Nicotinamide nucleotides [NADH + H+ / NAD+] 2.Flavo-proteins [FADH2 / FAD+]. 3.Ubiquinone: CoQ. 4. Cytochromes: b, c1, c, a, a3.

22. ETC ETC components are arranged in four complexes in the increasing order of their redox potentials from -4.2 for (NADH + H+) to +0.82 for O2. Complex I: NADH + H+----- CoQ reductase. II: Succinate ----- CoQ reductase. III: Co-Q ------- Cyt C reductase. IV: Cytochrome oxidase.

23. ETC

24. ATPsynthase[v ]

25. ATP synthase – Complex 5 • Integral protein in the inner mitochondrial membrane. • It has two units F0 & F1. • F0 acts as a protein channel. • F1 has ATP synthase activity.

27. Components of ETC 1.Nicotinamide nucleotides [NADH + H+ and NAD+] 2. flavo-proteins [ FADH2 and FAD+ ]

28. Components of ETC 3. Co- Q [ubiquinone]

29. Components of ETC 4. cytochromes

30. ETC • P;O ratio is the number of P atoms utilized To synthesize ATP for one atom of O2 oxidized P;O ratio for NADH + H+ is ‘3’ [three sites of ATP synthesis] P;O ratio for FADH2 is ‘2’ [two sites of ATP synthesis]

31. Theories of oxidative phosphorylation 1. Chemical coupling: Generation of ATP at substrate level. 2. Conformational coupling: Conformational changes in the molecules in mitochondrial membrane leads to ATP generation. 3. Chemi -osmotic theory: The proton gradient generated during electron transfer is utilized for ATP synthesis.

33. Inhibitors of ETC Site specific: 1. NADH + H+ to CoQ; 1.Rotenone 2.piericidin 3. amylobarbital 2. Cyt b to Cyt c1 1. Antimycin 2. BAL. 3. Cyt a3 toO2 1. HCN 2. H2S 3. CO.

34. Inhibitors of oxidative phosphorylation Uncouplers:2,3 dinitrophenol, 2,3 dinitrocresol Physiologicaluncouplers: Large doses of 1. Unconjugated bilirubin, 2. Thyroxine 3. Aspirin 4. Long chain fatty acids. 1. Oligomycin :Blocks ATP synthase activity. 2.Atractyloside : Block the proton flow into the mitochondrial matrix.