1. The Organic Chemistry of the Metabolic Pathways • Terpene Biosynthesis
Chapter 25
The Organic Chemistry of the Metabolic Pathways •
Terpene Biosynthesis
Paula Yurkanis Bruice
University of California,
Santa Barbara

2. Metabolism
metabolism = the reactions cells carry out to obtain the energy they need
and to synthesize the compounds they require
metabolism can be divided into two parts
catabolism: complex molecules simple molecules + energy
anabolism: simple molecules + energy complex molecules

3. Phosphoesters
DNA and RNA are Diesters of Phosphoric Acid

4. Phosphoric Acid Can be Dehydrated

5. ATP is a Monoester of Triphosphoric Acid

6. This Reaction Requires ATP

7. Transfer of a Phosphate Group from ATP to Glucose
Many phosphoryl transfer reactions occur in cells.

8. ATP Activates Carboxylate Ions so They can React with Nucleophiles

9. Attack of a Carboxylate Ion on the γ-Phosphorus

10. Attack of a Carboxylate Ion on the α-Phosphorus

11. Pyrophosphate is Hydrolyzed to Phosphate
Hydrolyzing pyrophosphate to phosphate ensures the irreversibility of the reaction.

12. The Reaction of a Nucleophile with ATP is a Highly Exergonic Reaction

13. Factors that Contribute to the Greater Stability of ADP and Phosphate Compared to ATP
[Pg. 1175]
1. Greater electrostatic repulsion in ATP
2. Greater solvent stabilization in the products
3. Greater electron delocalization in the products

14. The Four Stages of Catabolism
The reactions in the first stage
are hydrolysis reactions.
The products of the first stage are
converted to acetyl-CoA or to
citric acid cycle intermediates.
The acetyl-CoA formed in the
second sage enters the
citric acid cycle.
ATP is synthesized in the
fourth stage.

15. The Hydrolysis of Fats

16. What Happens to Glycerol?
A kinase is an enzyme that puts a phosphoryl group on its substrate.
Dihydroxyacetone phosphate is an intermediate in the glycolytic pathway.

17. What Does Zinc Do?
Zinc increases the acidity of the alcohol’s proton.

18. The Fatty Acid is Converted to a Fatty Acyl-CoA

19. β -Oxidation

20. The Conjugate Addition of Water
NAD+ oxidizes
the secondary alcohol
to a ketone.

21. A Reverse Claisen Condensation
Beta-oxidation removes one acetyl-CoA molecule at a time,
converting the entire fatty acids to acetyl-CoA molecules.

22. Catabolism of Carbohydrates
In the first stage of catabolism, an enzyme-catalyzed reaction hydrolyzes the carbohydrate to molecules of glucose.

23. An Enediol Rearrangement Converts Dihydroxyacetone Phosphate to Glyceraldehyde-3-Phosphate

24. The Mechanism for the Enediol Rearrangement
Compare this mechanism with the enediol rearrangement shown in Section 21.5.

25. glycolysis

26. Oxidizing Glyeraldehyde-3-phosphate to 1,3-Bisphosphoglycerate
NAD+ catalyzes this oxidation reaction.
(The mechanism is shown on page 1138.)

27. A Phosphate is Transferred to ADP to Form ATP

28. An Isomerization Reaction

29. An E1cb Reaction Converts 2-Phosphoglycerate to Phosphoenolpyruvate

30. A Phosphate is Transferred to ADP to Form ATP

31. An exergonic reaction drives the reaction that precedes it.
Coupled Reactions
An exergonic reaction drives the reaction that precedes it.

32. The mechanism of this reaction is shown on pages 1146−1147.
The Fate of Pyruvate
Aerobic conditions:
Pyruvate (the end product of glycolysis) is converted to acetyl-CoA,
which can enter the citric acid cycle.
The mechanism of this reaction is shown on pages 1146−1147.
Anaerobic conditions:

33. Fate of Pyruvate Under Anaerobic Conditions in Yeast

34. Catabolism of Proteins
In the first stage of catabolism,
enzyme-catalyzed hydrolysis of a protein forms amino acids.
The amino acids
can be metabolized to get energy.
can be used to make proteins.
can be use to make other compounds the body needs.

35. An Example of Amino Acid Catabolism

36. PKU is Caused by an Absence of Phenylalanine Hydroxylase
Without phenylalanine hydroxylase,
phenylalanine is transaminated to phenylpyruvate.

37. The Citric Acid Cycle
The citric acid cycle converts the acetyl group of acetyl-CoA to two molecules of CO2.
The series of eight reactions is called a cycle because the product of the eighth reaction is the reactant of the first reaction.

38. the citric acid cycle

39. An Aldol Addition Followed by Hydrolysis

40. An E2 Reaction Followed by the Conjugate Addition of Water

41. Oxidation, Decarboxylation,Tautomerization

42. The Overall Reaction is the Transfer of an Acyl Group to CoASH
The mechanism for this reaction is the same as that for the pyruvate dehydrogenase complex (pp. 1146–1147).

43. Succinyl-CoA to Succinate
A nucleophilic addition–elimination reaction
followed by transfer of a phosphate group to GDP.

44. The Mechanism for the Transfer of a Phosphate Group to GDP

45. GTP Transfers a Phosphate Group to ADP

46. Coenzyme Q10 is an Electron Acceptor
The electrons lost when NADH and FADH2 are oxidized are transferred to a system of linked electron acceptors. One of the first acceptors is coenzyme Q10.

47. Oxidative Phosphorylation
In the fourth stage of catabolism, NADH is oxidized back to NAD+ and FADH2 is oxidized back to FAD, thereby forming ATP.

48. Each Round of the Citric Acid Cycle
Forms 10 ATP

49. Anabolism (how cells form fats and oils)

50. glycolysis and
gluconeogeneis

51. The Mechanism for One of the Irreversible Reactions in Gluconeogenesis

52. Glucose-6-phosphate is a Feedback Inhibitor
A feedback inhibitor inhibits a step at the beginning of its synthesis.

53. Acetyl-CoA is an Allosteric Activator of One Enzyme and a Feedback Inhibitor of Another
A high concentration of acetyl-CoA signals that oxidation of glucose is not necessary, so pyruvate is converted to glucose instead of entering the citric acid cycle.

54. Amino Acid Biosynthesis

55. Biosynthesis of Serine
oxidation, transamination, hydrolysis

56. Terpenes Terpenes contain carbon atoms in multiples of five:
A monoterpene contains 10 carbons.
A sesquiterpene contains 15 carbons.
A diterpene contains 20 carbons.
A triterpene contains 30 carbons.

57. The Structures are Consistent with Joining Together Isoprene Units, Usually Head-to-Tail

58. The Five-Carbon Compound Actually Used for Biosynthesis is Isopentenyl Pyrophosphate

59. Conversion of Isopentenyl Pyrophosphate to Dimethylallyl Pyrophosphate
The biosynthesis of a terpene always starts with a dimethylallyl pyrophosphate.

60. Geranyl = 10 carbons

61. The Biosynthesis of Some Monoterpenes

62. Farnesyl = 15 carbons

63. Squalene is a Triterpene
Squalene is the precursor of cholesterol.
Cholesterol is the precursor of all the other steroid hormones.