1. Microbiology: A Systems Approach
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Microbiology: A Systems Approach
Cowan/Talaro
Chapter 8
Microbial Metabolism
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2. Chapter 8
Topics
Metabolism
Energy
Pathways
Biosynthesis

3. Metabolism
Catabolism
Anabolism
Enzymes

4. Catabolism
Enzymes are involved in the breakdown of complex organic molecules in order to extract energy and form simpler end products

5. Anabolism
Enzymes are involved in the use of energy from catabolism in order to synthesize macromolecules and cell structures from precursors (simpler products)

6. The relationship between catabolism and anabolism.
Fig. 8.1 Simplified model of metabolism

7. Enzymes Function Structure Enzyme-substrate interaction Cofactors
Regulation

8. Function Catalysts for chemical reactions
Lower the energy of activation

9. Structure Simple enzyme Conjugated enzyme Three-dimensional features
protein alone
Conjugated enzyme
protein and nonprotein
Three-dimensional features
Enable specificity
Active site or catalytic site

10. Conjugated enzymes contain a metallic cofactor, coenzyme, or both in order for it to function as a catalyst.
Fig. 8.2 Conjugated enzyme structure

11. Specific active sites (amino acids) arise due to the folding of the protein (enzyme).
Fig. 8.3 How the active site and specificity of the apoenzyme arise.

12. Enzyme-substrate interactions
Substrates specifically bind to the active sites on the enzyme
“lock-and-key”
Induced fit
Once the reaction is complete, the product is released and the enzyme reused

13. An example of the “lock-and-key” model, and the induced fit model.
Fig. 8.4 Enzyme-substrate reactions

14. Cofactors Bind to and activate the enzyme Ex. Metallic cofactors
Iron, copper, magnesium
Coenzymes

15. Coenzyme
Transient carrier - alter a substrate by removing a chemical group from one substrate and adding it to another substrate
Ex. vitamins

16. An example of how a coenzyme transfers chemical groups from one substrate to another.
Fig. 8.5 The carrier functions of coenzymes

17. Action Exoenzymes Endoenzymes Constitutive Induction or repression
Types of reactions

18. Exoenzymes are inactive while inside the cell, but upon release from the cell they become active. In contrast, endoenzymes remain in the cell and are active.
Fig. 8.6 Types of enzymes, as described by their location of action.

19. Constitutive enzymes are present in constant amounts, while regulated enzymes are either induced or repressed.
Fig. 8.7 Constitutive and regulated enzymes

20. Types of Reaction
Condensation
Hydrolysis
Transfer reactions

21. Condensation reactions are associated with anabolic reactions, and hydrolysis reactions are associated with catabolic reactions.
Fig. 8.8 Examples of enzyme-catalyzed synthesis
and hydrolysis reactions

22. Transfer reactions Transfer of electrons from one substrate to another
Oxidation and reduction
Oxidoreductase
Transfer of functional groups from one molecule to another
Transferases
Aminotransferases

23. Examples of oxidoreductase, transferase, and hydrolytic enzymes.
Table 8.A A sampling of enzymes, their substrates, and their reactions

24. Regulation
Metabolic pathways
Direct control
Genetic control

25. The different metabolic pathways are regulated by the enzymes that catalyze the reactions.
Fig.8.9 Patterns of
metabolism

26. Competitive inhibition and noncompetitive inhibition are examples of direct control (regulation) of the action of the enzymes.
Fig Examples of two common control mechanisms
for enzymes.

27. Genetic control
Repression
Induction

28. Repression is when end products can stop the expression of genes that encode for proteins (enzymes) which are responsible for metabolic reactions.
Fig One type of genetic control of enzyme synthesis

29. Summary of major enzyme characteristics.
Table 8.1 Checklist of enzyme characteristics

30. Energy Cell energetics Redox reaction Electron carrier
Exergonic
Endergonic
Redox reaction
Electron carrier
Adenosine Triphosphate (ATP)

31. The general scheme associated with metabolism of organic molecules, the redox reaction, and the capture of energy in the form of ATP.
Fig A simplified model that summarizes the cell’s
energy machine.

32. Redox reaction Reduction and oxidation reaction
Electron carriers transfer electrons and hydrogens
Electron donor
Electron acceptor
Energy is also transferred and captured by the phosphate in form of ATP

33. Electron carriers Coenzymes Respiratory chain carriers
Nicotinamide adenine dinucleotide (NAD)
Respiratory chain carriers
Cytochromes (protein)

34. Electron carriers, such as NAD, accept electrons and hydrogens from the substrate (organic molecule).
Fig Details of NAD reduction

35. Adenosine Triphosphate (ATP)
Temporary energy repository
Breaking of phosphates bonds will release free energy
Three part molecule
Nitrogen base
5-carbon sugar (ribose)
Chain of phosphates

36. The phosphates capture the energy and becomes part of the ATP molecule.
Fig The structure of adenosine triphosphate and its
partner compounds, ADP and AMP.

37. ATP can be used to phosphorylate an organic molecule such as glucose during catabolism.
Fig An example of phosphorylation of glucose by ATP

38. ATP can be synthesized by substrate-level phosphorylation.
Fig ATP formation by substrate-level phosphorylation

39. Pathways Catabolism Embden-Meyerhof-Parnas (EMP) pathway or glycolysis
Tricarboxylic acid cycle (TCA)
Respiratory chain
Aerobic
Anaerobic
Alternate pathways
Fermentation

40. A summary of the metabolism of glucose and the synthesis of energy.
Fig Overview of the flow, location, and products of
Pathways in aerobic respiration.

41. Aerobic respiration Glycolysis Tricarboxylic acid (TCA)
Electron transport

42. Glycolysis Oxidation of glucose
Phosphorylation of some intermediates (Uses two ATPs)
Splits a 6 carbon sugar into two 3 carbon molecules
Coenzyme NAD is reduced to NADH
Substrate-level-phosphorylation (Four ATPs are synthesized)

43. Glycolysis continued Water is generated Net yield of 2 ATPs
Final intermediates are two Pyruvic acid molecules

44. The glycolytic steps associated with the metabolism of glucose to pyruvic acid (pyruvate).
Fig Summary of glycolysis

45. TCA cycle
Each pyruvic acid is processed to enter the TCA cycle (two complete cycles)
CO2 is generated
Coenzymes NAD and FAD are reduced to NADH and FADH2
Net yield of two ATPs
Critical intermediates are synthesized

46. The steps associated with TCA cycle.
Fig The reaction of a single turn of the TCA cycle

47. Electron transport
NADH and FADH2 donate electrons to the electron carriers
Membrane bound carriers transfer electrons (redox reactions)
The final electron acceptor completes the terminal step (ex. Oxygen)

48. Electron transport continued
Chemiosmosis
Proton motive force (PMF)

49. Chemiosmosis entails the electron transport and formation of a proton gradient (proton motive force).
Fig The electron transport system and oxidative
phosphorylation

50. Electron transport chain
Mitochondria
eucaryotes
Cytoplasmic membrane
procaryotes

51. Total yield of ATP for one glucose molecule from aerobic respiration.
Table 8.4 Summary of aerobic respiration for
one glucose molecule

52. Anaerobic respiration
Similar to aerobic respiration, except nitrate or nitrite is the final electron acceptor

53. Fermentation Glycolysis only
NADH from glycolysis is used to reduce the organic products
Organic compounds as the final electron acceptors
ATP yields are small (per glucose molecule), compared to respiration
Must metabolize large amounts of glucose to produce equivalent respiratory ATPs

54. The fermentation of ethyl alcohol and lactic acid.
Fig The chemistry of fermentation systems

55. Types of fermenters Facultative anaerobes Strict fermenters
Fermentation in the absence of oxygen
Respiration in the presence of oxygen
Ex. Escherichia coli
Strict fermenters
No respiration
Ex. yeast

56. Products of fermentation
Alcoholic fermentation
Acidic fermentation
Mixed acid fermentation

57. An example of mixed acid fermentation and the diverse products synthesized.
Fig Miscellaneous products of pyruvate

58. Biosynthesis Anabolism Amphibolic Gluconeogenesis Beta oxidation
Amination
Transamination
Deamination
Macromolecules

59. Amphibolic Integration of the catabolic and anabolic pathways
Intermediates serve multiple purposes

60. Intermediates can serve to synthesize amino acids, carbohydrates and lipids.
Fig An amphibolic view of metabolism

61. Gluconeogenesis Pyruvate (intermediate) is converted to glucose
Occurs when the glucose supply is low

62. Beta oxidation
Metabolism of fats into acetyl, which can then enter the TCA cycle as acetyl CoA.

63. Examples of amination, transamination, and deamination.
Fig Reactions that produce and convert amino acids

64. Macromolecules Cellular building blocks Monosaccharides Amino acids
Fatty acids
Nitrogen bases
Vitamins