1. Bacterial metabolism Assist. Prof. Emrah Ruh NEU Faculty of Medicine
Department of Medical Microbiology

2. Bacterial metabolism
Metabolism: The sum of all chemical reactions within a living organism
Metabolism  Catabolism + anabolism

3. Bacterial metabolism Catabolism:
Chemical reactions that result in the breakdown of more complex organic molecules into simpler substances
Release energy (ATP; stored and used to power anabolic chemical reactions)

4. Bacterial metabolism Anabolism:
Chemical reactions in which simpler substances are combined to form more complex molecules
Require energy (ATP)

5. Bacterial metabolism
Catabolism + anabolism  Metabolism

6. Bacterial metabolism Adenosine Triphosphate (ATP)

7. Bacterial metabolism Adenosine Triphosphate (ATP)
Energy (ATP) is required for the anabolic reaction
ATP
ADP P +

8. Bacterial metabolism Adenosine Triphosphate (ATP)
Catabolic reactions release energy
The energy is stored as ATP
ATP
ADP P +

9. Bacterial metabolism Energy production
Oxidation-Reduction Reactions:
Oxidation: the removal of one or more electrons from a substrate. Protons (H+) are often removed with the electrons
Reduction of a substrate: its gain of one or more electrons

10. Bacterial metabolism Energy production
Oxidation-Reduction (Redox) Reactions:

11. Bacterial metabolism Energy production
Oxidation-Reduction (Redox) Reactions:
Nicotinamide adenine dinucleotide (NAD+) is the oxidized form; NADH is the reduced form

12. Bacterial metabolism Energy production
The generation of ATP:
Energy released during certain metabolic reactions can be trapped to form ATP from ADP and phosphate
Addition of a phosphate to a molecule is called phosphorylation

13. Bacterial metabolism Energy production (ATP generation)
The generation of ATP:
Oxidative phosphorylation
Substrate-level phosphorylation
Photophosphorylation
Chemiosmosis

14. Bacterial metabolism Energy production (ATP generation)
Oxidative phosphorylation:
Energy is released as electrons are passed to a series of electron acceptors (an electron transport chain) and finally to O2 or another inorganic compound
Energy released is utilized to make ATP by chemiosmosis

15. Bacterial metabolism Energy production (ATP generation)
Substrate-level phosphorylation:
A high-energy phosphate from a substrate in catabolism is added to ADP
An enzyme transfers the phosphate group to ADP to form ATP

16. Bacterial metabolism Energy production (ATP generation)
Photophosphorylation:
Energy from light is trapped by chlorophyll, and electrons are passed through a series of electron acceptors (an electron transport chain) 
Energy released during electron transfer is utilized to make ATP by chemiosmosis

17. Bacterial metabolism Energy production (ATP generation)
Chemiosmosis:
The energy from electron transfer through an electron transport chain drives proton pumps
The proton pumps move protons to one side of the membrane, increasing the concentration on one side and decreasing the concentration on the other side

18. Bacterial metabolism Energy production (ATP generation)
Chemiosmosis:
The protons diffuse down their concentration gradient through a membrane channel that has enzymatic (ATPase) activity
The energy of the protons moving through the channel drives phosphorylation of ADP to make ATP

19. Bacterial metabolism Energy production (ATP generation)
The generation of ATP:
Oxidative phosphorylation
Substrate-level phosphorylation
Photophosphorylation
Chemiosmosis

20. Bacterial metabolism Energy production (ATP generation)
The processes that use these mechanisms:
Cellular respiration (aerobic, anaerobic)
Fermentation
Photosynthesis

21. Bacterial metabolism Energy production (ATP generation)
Cellular respiration:
ATP is generated by oxidation of organic molecules, the passage of electrons down an electron transport chain, and chemiosmosis
The final electron acceptor:
Aerobic  O2
Anaerobic  Inorganic molecules (NO3-, SO4-2, CO3-2,…)

22. Bacterial metabolism Energy production (ATP generation)
Fermentation:
The final electron acceptor is an organic molecule
ATP production is accomplished by substrate- level phosphorylation 

23. Bacterial metabolism Energy production (ATP generation)
Photosynthesis:
ATP is generated by photophosphorylation
Plants, algae, cyanobateria,...

24. Bacterial metabolism Energy production (ATP generation)

25. Bacterial metabolism Metabolic diversity among organisms
Carbon source
Autotrophs
Heterotrophs
Energy source
Phototrophs
Chemotrophs

26. Bacterial metabolism Metabolic diversity among organisms
Carbon source
Autotrophs
Self-feeders; and use CO2 as a carbon source
Heterotrophs
Feed on others and use organic sources of carbon

27. Bacterial metabolism Metabolic diversity among organisms
Energy source
Phototrophs
Use light as an energy source
Chemotrophs
Use redox reactions of organic or inorganic compounds as an energy source

28. Bacterial metabolism Metabolic diversity among organisms

29. Bacterial metabolism Metabolic diversity among organisms

30. Bacterial metabolism Carbohydrate catabolism
Most of a cell’s energy is produced from the oxidation of carbohydrates
Glucose is the most commonly used carbohydrate
The two major types of glucose catabolism:
Respiration  glucose is completely broken down
Fermentation  glucose is partially broken down

31. Bacterial metabolism Carbohydrate catabolism

32. Bacterial metabolism Carbohydrate catabolism
Oxidation of glucose
Glycolysis (Embden-Meyerhof pathway)
Pentose phosphate pathway
Entner-Doudoroff pathway

33. Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway)
Stage 1

34. Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway)
The most common pathway for the oxidation of glucose
Pyruvic acid is the end-product
Two ATP and two NADH molecules are produced from one glucose molecule

35. Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway)

36. Carbohydrate catabolism Glycolysis (Embden-Meyerhof pathway)

37. Bacterial metabolism Carbohydrate catabolism
Oxidation of glucose
Glycolysis (Embden-Meyerhof pathway)
Pentose phosphate pathway
Entner-Doudoroff pathway

38. Bacterial metabolism Carbohydrate catabolism
Oxidation of glucose

39. Carbohydrate catabolism Cellular respiration
During respiration, organic molecules are oxidized 
Energy is generated from the electron transport chain
The final electron acceptor:
Aerobic respiration  O2
Anaerobic respiration  Inorganic molecule

40. Carbohydrate catabolism Aerobic respiration
Stage 2

41. Carbohydrate catabolism Aerobic respiration
From one molecule of glucose, oxidation in the Krebs cycle produces six molecules of NADH, two molecules of FADH2, and two molecules of ATP

42. Carbohydrate catabolism Aerobic respiration
The Krebs Cycle

43. Carbohydrate catabolism Aerobic respiration
Stage 3 (Electron transport system)

44. Carbohydrate catabolism Aerobic respiration
Electrons are brought to the electron transport chain by NADH
The electron transport chain consists of carriers, including flavoproteins, cytochromes, and ubiquinones
Electrons are passed from one carrier to the next, the energy is used to drive proton pumps

45. Carbohydrate catabolism Aerobic respiration
Electron transport system

46. Carbohydrate catabolism Aerobic respiration
Two NADH molecules from glycolysis
Two NADH molecules from formation of acetyl CoA
Six NADH molecules from Krebs cycle
Two FADH molecules from Krebs cycle
One NADH: Three ATP molecules
One FADH: Two ATP molecules

47. Carbohydrate catabolism Aerobic respiration - Chemiosmosis
Protons being pumped across the membrane generate proton motive force as electrons move through a series of acceptors or carriers
Energy produced from movement of the protons back across the membrane is used by ATP synthase to make ATP from ADP and phosphate

48. Carbohydrate catabolism Aerobic respiration - Chemiosmosis
Electron carriers:
Eukaryotes  inner mitochondrial membrane
Prokaryotes  plasma membrane

49. Carbohydrate catabolism Aerobic respiration - Summary
Aerobic prokaryotes:
38 ATP molecules are produced from complete oxidation of a glucose molecule in glycolysis, the Krebs cycle, and the electron transport chain
Eukaryotes:
36 ATP molecules are produced from complete oxidation of a glucose molecule

50. Carbohydrate catabolism Aerobic respiration - Summary
Aerobic prokaryotes

51. Carbohydrate catabolism Summary
Aerobic prokaryotes

52. Carbohydrate catabolism Anaerobic respiration
The final electron acceptors: Inorganic molecules (eg, NO3-, SO4-2, and CO3-2)
NO3- (nitrate) is reduced to NO2- (nitrite)
SO4-2 (sulfate) is reduced to H2S (hydrogen sulfide)
CO3-2 (carbonate) is reduced to CH4 (methane)
The total ATP yield is less than in aerobic respiration (only part of the Krebs cycle operates)

53. Carbohydrate catabolism Fermentation

54. Carbohydrate catabolism Fermentation
Releases energy from sugars or other organic molecules by oxidation
Does not require O2, the Krebs cycle, or an electron transport chain
Can sometimes occur in the presence of O2
Uses an organic molecule as the final electron acceptor

55. Carbohydrate catabolism Fermentation
Produces two ATP molecules by substrate-level phosphorylation
Electrons removed from the substrate reduce NAD+ to NADH
NADH molecules are then oxidized to NAD for lactic acid or alcohol fermentation
Fermentation without aerobic electron transport and a complete Krebs cycle produces only two ATP molecules per glucose

56. Carbohydrate catabolism Fermentation

57. Carbohydrate catabolism Fermentation

58. Carbohydrate catabolism Fermentation
Lactic acid fermentation
Alcohol fermentation

59. Carbohydrate catabolism Fermentation

60. Carbohydrate catabolism Fermentation
Lactic acid fermentation:
Pyruvic acid is reduced by NADH to lactic acid
Lactic acid fermenters include bacteria (eg, Streptococcus and Lactobacillus)
Making milk into yogurt and cheese!
Lactic acid can be fermented to propionic acid and CO2 by Propionibacterium freudenreichii (Swiss cheese)

61. Carbohydrate catabolism Fermentation
Alcohol fermentation:
Acetaldehyde is reduced by NADH to produce ethanol
Alcohol fermenters include yeasts and bacteria
Making wine, whiskey, bread, etc…!
Ethanol can be fermented to acetic acid (vinegar) by Acetobacter
Acetic acid can be fermented to methane by Methanosarcina

62. Carbohydrate catabolism ATP yield – Summary
According to the quantity of ATP yield:
Aerobic respiration
Anaerobic respiration
Fermentation
Energy

63. Carbohydrate catabolism ATP yield – Summary

64. Bacterial metabolism Grouping  Carbohydrate utilization
Type of carbohydrate utilization:
Oxidative bacteria
Fermentative bacteria
Nonsaccharolytic bacteria (lipid and protein catabolism)

65. Bacterial metabolism Lipid and protein catabolism
Lipids:
Lipases hydrolyze lipids into glycerol and fatty acids
Catabolic products can be further broken down in glycolysis and the Krebs cycle

66. Bacterial metabolism Lipid and protein catabolism
Amino acids:
Transamination (transfer of NH2), decarboxylation (removal of COOH), and dehydrogenation (H2) reactions convert the amino acids into substances (alkaline conditions)
Catabolized substances enter the glycolytic pathway or Krebs cycle

67. Bacterial metabolism Lipid and protein catabolism

68. Bacterial metabolism Anabolism
Polysaccharide biosynthesis
Lipid biosynthesis
Amino acid and protein biosynthesis
Purine and pyrimidine biosynthesis

69. Anabolism Polysaccharide biosynthesis
Glucose (and other simple sugars - monosaccharides) may be synthesized from intermediates in glycolysis and the Krebs cycle 
Monosaccharides can be linked together to make polysaccharides

70. Anabolism Polysaccharide biosynthesis
(Adenosine diphosphoglucose)
(Uridine diphosphoglucose)
(UDP-N-acetylglucosamine)

71. Anabolism Lipid biosynthesis
Lipids are synthesized from fatty acids and glycerol

72. Anabolism Lipid biosynthesis

73. Anabolism Amino acid and protein biosynthesis
Amino acids are required for protein biosynthesis
All amino acids can be synthesized either directly or indirectly from intermediates of carbohydrate metabolism, particularly from the Krebs cycle
Transamination or amination reactions:
Amino acid = Organic acids + an amine (NH2) group

74. Anabolism Amino acid and protein biosynthesis

75. Anabolism Amino acid and protein biosynthesis
Glutamic acid  a-Ketoglutaric acid + NH2
Aspartic acid  Oxaloacetic acid + NH2

76. Anabolism Purine and pyrimidine biosynthesis
The sugars composing nucleotides are derived from either the pentose phosphate pathway or the Entner-Doudoroff pathway
Carbon and nitrogen atoms from certain amino acids (aspartic acid, glycine, glutamic acid) form the backbones of the purines and pyrimidines
Includes DNA, RNA, ATP, NAD,…

77. Anabolism Purine and pyrimidine biosynthesis

78. Bacterial metabolism The integration of metabolism
Anabolic and catabolic reactions are integrated through a group of common intermediates
Such integrated metabolic pathways are referred to as amphibolic pathways

79. Bacterial metabolism