Lecture 26 Energy conversion (continued)

1. Lecture 26 Energy conversion (continued) Substrate Oxidation, Generation of reduced high-energy intermediates and their oxidation by oxygen

2. http://www.microscopyu.com/galleries/fluorescence/cells/hela/hela.htmlhttp://www.microscopyu.com/galleries/fluorescence/cells/hela/hela.html

3. Why oxygen? Electron re-distribution from less electronegative to more electronegative atoms occurs with massive energy release: Electronegativity of common elements: H < C < S < N < O …Cl < F Identify the substance and the reduction state of the first carbon (red)

4. Enthalpies of oxidation (combustion) hydrogen (MW 2) H2 + ½O2 → H2O -286 kJ/mol (-68.4 kCal/mol) methane (MW 16) CH4 + 3O2 → CO2 + 2H2O -891 kJ/mol (213) glucose (MW 180.2) C6H12O6 + 6O2→ 6CO2 + 6H2O -2840 kJ/mol (-680) palmitic acid (MW 256.4) C16H32O2 + 31O2 – 16CO2 + 16H2O - 9730 kJ/mol (-2328) Compare caloric capacities of the substrates

5. Oxidation-reduction (Red-ox) reactions usually lead to re-distribution of electron densities or complete transfer of electrons resulting in change of ionization state. Fe2+ + Cu2+→ Fe3+ + Cu+ or in the form of half-reactions: Fe2+ → Fe3+ + e Cu2+ + e → Cu+ In biological systems oxidation is often coupled to dehydrogenation. 1. Direct transfer of electrons 2. As a transfer of H atoms or removal of H atoms coupled to production of H+ 3. As a Hydride ion :H– 4. Through direct combination with oxygen R-CH3 + (½)O2→ R-CH2-OH

6. Reduction potentials for mixtures of reductant/oxidant (hlf-reaction potentials) are measured using the standard hydrogen electrode 2H+ + 2e → H2 Mg2+ + 2e → Mg (metal) http://www.chemguide.co.uk/physical/redoxeqia/eomgdiag.gif

7. Standard Reduction potentials for some half-reactions, Volt ½ O2 + 2H+ + 2e → H2O +0.816 Fe3+ + e → Fe2+ +0.771 Cytochrome c (Fe3+) + e → Cytochrome c (Fe2+) +0.254 Fumarate2- +2H+ + 2e → succinate2- +0.031 2H+ + 2e → H2 (standard condition)0 Pyruvate + 2H+ + 2e → lactate -0.185 FAD + 2H+ + 2e → FADH2 -0.219 S + 2H+ + 2e → H2S -0.243 NAD+ + H+ + 2e → NADH -0.320 NADP+ + H+ + 2e → NADPH -0.324 α-ketoglutarate + CO2 + 2H+ + 2e → isocytrate -0.38 2H+ + 2e → H2 (pH 7) -0.414 Standard Reduction potentials for some half-reactions, Volt ½ O2 + 2H+ + 2e → H2O +0.816 Fe3+ + e → Fe2+ +0.771 Cytochrome c (Fe3+) + e → Cytochrome c (Fe2+) +0.254 Fumarate2- +2H+ + 2e → succinate2- +0.031 2H+ + 2e → H2 (standard condition, pH0)0 Pyruvate + 2H+ + 2e → lactate -0.185 FAD + 2H+ + 2e → FADH2 -0.219 S + 2H+ + 2e → H2S -0.243 NAD+ + H+ + 2e → NADH -0.320 NADP+ + H+ + 2e → NADPH -0.324 α-ketoglutarate + CO2 + 2H+ + 2e → isocytrate -0.38 2H+ + 2e → H2 (pH 7) -0.414

8. NADH + H+ + ½ O2→ NAD+ + H2O NAD+ + H+ + 2e → NAD -0.320 V ½ O2 + 2H+ + 2e → H2O +0.816 V total difference 1.14 V DG = -nFEo = -220 kJ/mol

11. Stage 1 (in the cytosol)

15. NAD NAD+ + H+ +2e- NADH half reaction (-0.32 V) FAD has smaller reducing potential (-0.219 V) so its reduction can be coupled to a less energetically favorable oxidation reaction

22. Beta-Oxidation of fatty acids R= CH3-(CH2)n- R= CH3-(CH2)n-2-

23. When succinate and oxygen are given to mitochondria, they release H+

24. Electron transport chain Complex I II III IV Energy released in forming water is stored as a PMF Energy is divided into smaller units ~10-12 protons per water molecule

25. Iron-sulfur cluster (Fe-S) Heme

27. CoQ accepts both electrons and protons

31. Why add valinomycin?

32. What conditions are necessary for the experiment to work? • poorly-buffered medium • Valinomycin/potassium • A substrate…NOT NADH…as stated in your book Is ATP synthesis the reason for the pH returning to the original value?...

34. Oxidation rate is slow Why? Oxidation rate is fast Why?