1. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A; Krebs cycle; electron transport chains and chemiosmotic phosphorylation mechanism: andrew.pearson@uwimona.edu.jm

4. FAD NAD + FADH 2 NADH

5. Pyruvate and acetyl CoA are important metabolites at the intersection of many carbon- metabolising pathways. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A

6. Pyruvate and acetyl CoA are important metabolites at the intersection of many carbon- metabolising pathways. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A

7. Pyruvate Dehydrogenase Complex Pyruvate Carboxylase Metabolic relationship between carbohydrate and fat catabolism Some amino acids

8. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A 1. Glycolysis by either the EMP pathway, or variants such as PPP/HMP.

9. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Recall that PK is an important regulatory enzyme in some cells.

10. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A 2. Aerobic oxidation of lactate, e.g. by heart or liver isoenzymes of Lactate dh.

11. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A 3.O xidative deamination of alanine, e.g. by liver after release from skeletal muscle during fasting.

12. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Lets us now look at pyruvate dehydrogenase

13. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A

14. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A

15. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A

16. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A pdh reaction mechanism E 1 = Pyruvate dehydrogenase E 2 = Dihydrolipoyl transacetylase E 3 = Dihydrolipoyl dehydrogenase

17. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Pdh is regulated by reversible, inhibitory phosphorylation of E 1.

18. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Pdh is regulated by 4 reversible, inhibitory kinases of E 1. The kinases have differing tissue specificities. The kinases are activated by increasing the ratios of: [NADH]/[NAD]; [acetyl CoA]/[CoA]; [ATP]/[ADP] The kinases are inhibited by pyruvate. Insulin stimulates dephosphorylyation.

19. Pyruvate dehydrogenase kinases 1 – 4, with different tissue specificities “Pyruvate dehydrogenase kinase”, actually…. Phosphorylation sites on Pdh subunit E 1 Pyruvate dehydrogenase complex Pyruvate dehydrogenase phosphatase Regulation of the Pyruvate Dehydrogenase Complex

20. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Apart from carbohydrates, carbons from other molecules can form acetyl CoA. CHO

21. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Parts of leucine isoleucine tryptophan are degraded to acetyl CoA

22. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Lets us now look at fatty acid degradation

23. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A

24. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Figure 3 Modulation of CPT I activity by carbohydrates The pathway shown in red is the established pathway for the inhibition of hepatic CPT activity by carbohydrates. The other pathways shown are alternative routes that may be operative in heart Abbreviations : CPT, carnitine palmitoyl transferase ; CAT, carnitine acetyl transferase.

25. BC21D: Bioenergetics & Metabolism The formation of Acetyl Coenzyme A Just to remind you where we are going with this!

26. The major metabolic role of the Krebs cycle in most aerobes is the oxidative degradation of acetate to two molecules of CO 2 and some high energy reducing equivalents.

27. The Krebs cycle BC21D: Bioenergetics & Metabolism

28. Citrate synthase This is control point in some bacteria: the Krebs cycle is not partitioned from the cytosol. ATP is a negative modulator, raising the enzyme’s K m value for acetyl CoA

29. BC21D: Bioenergetics & Metabolism Aconitase Aconitate is not normally released from the enzyme Aconitase contains an iron-sulphur centre

30. BC21D: Bioenergetics & Metabolism Isocitrate dehydrogenase NADH + H + This is one of the control points of the Krebs cycle. It is an allosteric enzyme: ADP is the positive modulator enhancing the binding of isocitrate and NAD +. NADH is a competitive inhibitor of NAD + binding. ATP also inhibits. NAD +

31. BC21D: Bioenergetics & Metabolism α-ketoglutarate dehydrogenase complex NADH + H + NAD + Another control point of the Krebs cycle

32. BC21D: Bioenergetics & Metabolism (a) animal α-KG dh is very sensitive to ADP, Pi, and Ca 2+ ; (b) these positive effectors increase the affinity of α-KG dh to α -ketoglutarate; (c) α-KG dh is inhibited by ATP, NADH, and succinyl-CoA; (d) the ATP effect is realized mainly via opposition to ADP activation; (e) NADH, in addition to inhibiting the dihydrolipoamide dehydrogenase component of the enzyme complex (competitively versus NAD+), decreases the affinity of α -ketoglutarate dehydrogenase to its substrate; (f) bacterial and plant α-KG dh are activated by AMP instead of ADP. These main effects form the basis of short term regulation of α-KG dh.

33. BC21D: Bioenergetics & Metabolism Succinate thiokinase GTP GDP + P i

34. BC21D: Bioenergetics & Metabolism Succinate dehydrogenase complex FADH 2

35. BC21D: Bioenergetics & Metabolism Malate dehydrogenase NADH + H +

36. BC21D: Bioenergetics & Metabolism Amino acids can feed their carbons into the Krebs cycle for gluconeogenesis. Recall when and in which cells this occurs.

37. BC21D: Bioenergetics & Metabolism Amino acids with direct linkages to the Krebs cycle are especially important.

38. BC21D: Bioenergetics & Metabolism Possible metabolic outputs from the Krebs cycle From Nelson & Cox

39. BC21D: Bioenergetics & Metabolism From Stryer

40. BC21D: Bioenergetics & Metabolism Anaerobes lacking α-KG dh therefore have an incomplete Krebs cycle.

41. BC21D: Bioenergetics & Metabolism Some plants, invertebrates and fungi have the glyoxylate cycle for converting two acetates into succinate, thus are able to use fatty acids for gluconeogenesis.

42. BC21D: Bioenergetics & Metabolism

43. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

44. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

45. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism Collecting light energy from the solar (or an artificial) source is a major alternative to carbon catabolism.

46. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism Recall this image from last year. It highlights the similarities between different energy metabolisms.

47. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

48. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

50. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

56. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

57. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

58. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

59. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

60. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

61. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

62. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

63. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

64. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

65. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

66. Diagram from Lodish et al

74. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

75. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

76. electron transport & bioenergetics BC21D: Bioenergetics & Metabolism

78. 78 chemiosmotic mechanism BC21D: Bioenergetics & Metabolism The generation of a proton motive force across a biomembrane is a common bioenergetic mechanism.

79. 79 chemiosmotic mechanism BC21D: Bioenergetics & Metabolism Proton gradients are used to drive a number of energy consuming reactions.

80. 80 chemiosmotic mechanism BC21D: Bioenergetics & Metabolism

81. 81 chemiosmotic mechanism BC21D: Bioenergetics & Metabolism

82. 82 chemiosmotic mechanism BC21D: Bioenergetics & Metabolism

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