Chapter 5

1. Chapter 5 Microbial Metabolism

2. Microbial Metabolism • Metabolism is the sum of the chemical reactions in an organism. • Catabolism is the energy-releasing processes. • Anabolism is the energy-using processes.

3. Microbial Metabolism • Catabolism provides the building blocks and energy for anabolism. Figure 5.1

4. A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell. • Metabolic pathways are determined by enzymes. • Enzymes are encoded by genes.

5. The collision theory states that chemical reactions can occur when atoms, ions, and molecules collide. • Activation energy is needed to disrupt electronic configurations. • Reaction rate is the frequency of collisions with enough energy to bring about a reaction. • Reaction rate can be increased by enzymes or by increasing temperature or pressure.

6. Enzymes Figure 5.2

7. Enzymes • Biological catalysts • Specific for a chemical reaction; not used up in that reaction • Apoenzyme: protein • Cofactor: Non-protein component • Coenzyme: Organic cofactor • Holoenzyme: Apoenzyme + cofactor

8. Enzymes Figure 5.3

9. Important Coenzymes • NAD+ • NADP+ • FAD • Coenzyme A

10. Enzymes • The turnover number is generally 1-10,000 molecules per second. Figure 5.4

11. Enzyme Classification • Oxidoreductase Oxidation-reduction reactions • Transferase Transfer functional groups • Hydrolase Hydrolysis • Lyase Removal of atoms without hydrolysis • Isomerase Rearrangement of atoms • Ligase Joining of molecules, uses ATP

12. Factors Influencing Enzyme Activity • Enzymes can be denatured by temperature and pH Figure 5.6

13. Factors Influencing Enzyme Activity • Temperature Figure 5.5a

14. Factors Influencing Enzyme Activity • pH Figure 5.5b

15. Factors Influencing Enzyme Activity • Substrate concentration Figure 5.5c

16. Factors Influencing Enzyme Activity • Competitive inhibition Figure 5.7a, b

17. Factors Influencing Enzyme Activity

18. Competitive inhibition

19. Factors Influencing Enzyme Activity • Noncompetitive inhibition Figure 5.7a, c

20. Factors Influencing Enzyme Activity • Feedback inhibition Figure 5.8

21. Ribozymes • RNA that cuts and splices RNA

22. Oxidation-Reduction • Oxidation is the removal of electrons. • Reduction is the gain of electrons. • Redox reaction is an oxidation reaction paired with a reduction reaction. Figure 5.9

23. Oxidation-Reduction • In biological systems, the electrons are often associated with hydrogen atoms. Biological oxidations are often dehydrogenations. Figure 5.10

24. The Generation of ATP • ATP is generated by the phosphorylation of ADP.

25. The Generation of ATP • Substrate-level phosphorylation is the transfer of a high-energy PO4- to ADP.

26. The Generation of ATP • Energy released from the transfer of electrons (oxidation) of one compound to another (reduction) is used to generate ATP by chemiosmosis.

27. The Generation of ATP • Light causes chlorophyll to give up electrons. Energy released from the transfer of electrons (oxidation) of chlorophyll through a system of carrier molecules is used to generate ATP.

28. Metabolic Pathways

29. Carbohydrate Catabolism • The breakdown of carbohydrates to release energy • Glycolysis • Krebs cycle • Electron transport chain

30. Glycolysis • The oxidation of glucose to pyruvic acid, produces ATP and NADH.

31. Preparatory Stage Preparatory Stage Glucose • 2 ATPs are used • Glucose is split to form 2 Glucose-3-phosphate 1 Glucose 6-phosphate 2 Fructose 6-phosphate 3 Fructose 1,6-diphosphate 4 5 Glyceraldehyde 3-phosphate (GP) Dihydroxyacetone phosphate (DHAP)

32. Energy-Conserving Stage 6 • 2 Glucose-3-phosphate oxidized to 2 Pyruvic acid • 4 ATP produced • 2 NADH produced 1,3-diphosphoglyceric acid 7 3-phosphoglyceric acid 8 2-phosphoglyceric acid 9 Phosphoenolpyruvic acid (PEP) 10 Pyruvic acid

33. Glycolysis • Glucose + 2 ATP + 2 ADP + 2 PO4– + 2 NAD+2 pyruvic acid + 4 ATP + 2 NADH + 2H+

34. Alternatives to Glycolysis • Pentose phosphate pathway: • Uses pentoses and NADPH • Operates with glycolysis • Entner-Doudoroff pathway: • Produces NADPH and ATP • Does not involve glycolysis • Pseudomonas, Rhizobium, Agrobacterium

35. Cellular Respiration • Oxidation of molecules liberates electrons for an electron transport chain • ATP generated by oxidative phosphorylation

36. Intermediate Step • Pyruvic acid (from glycolysis) is oxidized and decarboyxlated Figure 5.13.1

37. Krebs Cycle • Oxidation of acetyl CoA produces NADH and FADH2

38. Krebs Cycle Figure 5.13.2

39. The Electron Transport Chain • A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain. • Energy released can be used to produce ATP by chemiosmosis.

40. Figure 5.14

41. Chemiosmosis Figure 5.15

42. Chemiosmosis Figure 5.16.2

43. Respiration • Aerobic respiration: The final electron acceptor in the electron transport chain is molecular oxygen (O2). • Anaerobic respiration: The final electron acceptor in the electron transport chain is not O2. Yields less energy than aerobic respiration because only part of the Krebs cycles operations under anaerobic conditions.

44. Anaerobic respiration

46. Energy produced from complete oxidation of 1 glucose using aerobic respiration

47. ATP produced from complete oxidation of 1 glucose using aerobic respiration • 36 ATPs are produced in eukaryotes.

48. Fermentation • Releases energy from oxidation of organic molecules • Does not require oxygen • Does not use the Krebs cycle or ETC • Uses an organic molecule as the final electron acceptor

49. Fermentation Figure 5.18b

50. Fermentation • Alcohol fermentation. Produces ethyl alcohol + CO2 • Lactic acid fermentation. Produces lactic acid. • Homolactic fermentation. Produces lactic acid only. • Heterolactic fermentation. Produces lactic acid and other compounds.