1. Microbial Metabolism: Catabolic and Anabolic Pathways
Microbial Metabolism: The Chemical Crossroads of Life
Microbiology: A Systems Approach
Microbial Metabolism: Catabolic and Anabolic Pathways
Chapter 8 (p )
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Chapter 8, pages 198 to 231

2. Learning Objectives: Explain the overall function of metabolic pathway
Describe the chemical reactions in glycolysis
Explain the products of the Krebs cycle
Describe the chemiosmotic model for ATP generation
Compare and contrast aerobic and anaerobic respiration
Describe the chemical reactions and list some products of fermentation.
Describe how lipids and proteins undergo catabolism
Define amphibolic pathways
Contrast oxygenic and anoxygenic photosynthesis.

3. Metabolic Pathways

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

6. Glycolysis
Oxidation of glucose to pyruvic acid
Produces ATP and NADH.

7. Preparatory Stage Two ATPs are used1
Two ATPs are used
Glucose is split to form two phosphorylated 3-carbon sugars 3 4 5

8. Energy-Conserving Stage
Two 3-carbon sugars oxidized to two Pyruvic acid molecules
Four ATP produced (substrate level phosphorylation)
Two NADH produced 9

9. Microbial Metabolism: The Chemical Crossroads of Life
Glycolysis Summary
Microbiology: A Systems Approach
One glucose is used
Partial oxidation of the sugar, 2 pyruvates are end products
Two NADH are reduced
2 ATP are consumed, 4 ATP total are made, net of 2 ATP produced
Chapter 8, pages 198 to 231

10. Intermediate Step
Pyruvic acid (from glycolysis) is oxidized and decarboxylated.

11. Krebs Cycle
Complete oxidation of acetyl CoA to CO2 produces NADH and FADH2.

12. Microbial Metabolism: The Chemical Crossroads of Life
Krebs Cycle Summary
Microbiology: A Systems Approach
Pyruvate 1
3 CO2
4 NADH
1 FADH2
1 ATP
Pyruvate 2
3 CO2
4 NADH
1 FADH2
1 ATP
Glucose has now been completely oxidized to carbon dioxide
Electrons are temporarily on carrier molecules
2 ATP total made by substrate level phosphorylation
Chapter 8, pages 198 to 231

13. 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.

14. Electron Transport System
NADH oxidized
Electrons pass through membrane carriers
Protons pumped out (work is done)
Electrons accepted by an inorganic molecule
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Cell wall H H H H H H H H H H H
Cytochromes H H H
Cytoplasm H H
ATP synthase
ADP
Cell membrane
with ETS H
ATP H H H

15. Microbial Metabolism: The Chemical Crossroads of Life
Aerobic Respiration
Microbiology: A Systems Approach
The electron acceptor is an oxygen
This is a very good acceptor
Yields water upon reduction
Because so much energy is released, the cell can pump out about 10 protons
Occurs in bacterial membrane and mitochondria of eukaryotes
Chapter 8, pages 198 to 231

16. Anaerobic Respiration
Microbial Metabolism: The Chemical Crossroads of Life
Anaerobic Respiration
Microbiology: A Systems Approach
The electron acceptor is not oxygen
Examples: nitrate, nitrite, and sulfate
These are mediocre acceptors – not as good as oxygen
Yields other inorganic molecules upon reduction
Less favorable reactions pump out fewer protons
Chapter 8, pages 198 to 231

17. Anaerobic Respiration
Electron acceptor
Products
NO3–
NO2–, N2 + H2O
SO4–
H2S + H2O
CO32 –
CH4 + H2O

18. Chemiosmosis Proton gradient is potential energy
Allowing protons back into the cell can be coupled to work
3 protons entering drive the synthesis of 1 ATP
Oxidative phosphorylation

19. Aerobic Respiration Yield
Microbial Metabolism: The Chemical Crossroads of Life
Aerobic Respiration Yield
Microbiology: A Systems Approach
1 Glucose  6 CO2
2 ATP from glycolysis
2 NADH from glycolysis  6 ATP
2 ATP from Krebs cycle substrate level
8 NADH from Krebs cycle  24 ATP
2 FADH2 from Krebs cycle  4 ATP
Total ATP per glucose
Chapter 8, pages 198 to 231

20. Microbial Metabolism: The Chemical Crossroads of Life
Fermentation
Microbiology: A Systems Approach
Performed by anaerobic microorganisms
Does not use Krebs cycle or ETC
Primary purpose: Regenerate NAD for reuse
The electron acceptor is an organic molecule
Secondary purpose: Generate additional energy
Energy yields are very small
Chapter 8, pages 198 to 231

21. Microbial Metabolism: The Chemical Crossroads of Life
Fermentation
Microbiology: A Systems Approach
NADH oxidized
Organic molecule reduced
Many possible end products
Lactic acid
Ethanol
Vinegar
Acetone
AEROBIC RESPIRATION
ANAEROBIC RESPIRATION
FERMENTATION
Glycolysis
Glycolysis
Glycolysis
Glucose
(6C)
Glucose
(6C)
Glucose
(6C)
ATP
ATP
ATP
NADH
2pyruvate
(3C)
NADH
2pyruvate
NADH
(3C)
2pyruvate
(3C)
CO2
CO2
CO2
Acety lCoA
Acety lCoA
FADH2
System: Homolactic bacteria;
human muscle
FADH2
System: Yeasts
NADH
Krebs
CO2
NADH
Krebs
CO2
Lactic acid
Acetaldehyde
ATP
ATP
Ethanol
Electrons
Electrons
Or other alcohols,
acids, gases
Electron transport
Electron transport
Glucose
acceptor.
O2 is final electron
Non oxygen electron acceptors (examples: SO42–, NO3–, CO32– )
acetaldehyde, etc.).
electron accept or (pyruvate,
An organic molecule is final
NAD
ATP produced = 38
ATP produced = 2 to 36
ATP produced = 2
NADH
Glycolysis H H C C C OH H O O
Pyruvic acid
CO2 H H C C H H O
Acetaldehyde
NADH
NAD H H H H
O H
NAD O H C C OH H C C C O H H H H H
Ethyl alcohol
Lactic acid
Chapter 8, pages 198 to 231

22. Fermentation

23. 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.

24. Pathway
Eukaryote
Prokaryote
Glycolysis
Cytoplasm
Intermediate step
Krebs cycle
Mitochondrial matrix
ETC
Mitochondrial inner membrane
Plasma membrane

25. Lipid Catabolism
Figure 5.20

26. Protein Catabolism Protein Amino acids Organic acid Krebs cycle
Extracellular proteases
Protein
Amino acids
Deamination, decarboxylation, dehydrogenation
Organic acid
Krebs cycle

27. Amphibolism GLUCOSE Enzymes Membranes Cell wall Storage Membranes
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Enzymes
Membranes
Cell wall
Storage
Membranes
Storage
Chromosomes
Cell
structure
Nucleic
acids
Starch
Cellulose
Lipids
Fats
Anabolism
Proteins
Macromolecule
Nucleotides
Amino acids
Carbohydrates
Fatty acids
Building block
Deamination
Beta oxidation
GLUCOSE
Glycolysis
Metabolic
pathways
Pyruvic acid
Acetyl coenzyme A
Catabolism
Krebs
cycle
Simple
products
NH3
CO2
H2O

28. Photosynthesis
Photo: Conversion of light energy into chemical energy (ATP)
Light-dependent (light) reactions
Synthesis: Fixing carbon into organic molecules
Light-independent (dark) reaction, Calvin-Benson cycle

29. Oxygenic Photosynthesis
Chlorophyll pigments
Thylakoid membrane
Capture light energy
Electron transport
Photophosphorylation
Makes NADH and ATP
Oxygen produced
Algae, plants, and cyanobacteria

31. Anoxygenic Photosynthesis
Microbial Metabolism: The Chemical Crossroads of Life
Anoxygenic Photosynthesis
Microbiology: A Systems Approach
Purple bacteria (similar to photosystem II)
Make ATP
Can’t make NADH
No oxygen produced
Green bacteria (similar to photosystem I)
Also make NADH
Chapter 8, pages 198 to 231

32. Ribulose-1,5-bisphosphate
Calvin Benson Cycle
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Fix carbon dioxide
Autotrophs
Reverse of glycolysis
6 CO2  Glucose
CO2 P P
Splitting
6 Carbon
intermediate
3-phosphoglyceric
acid P P
Ribulose-1,5-bisphosphate
5Carbon P
ATP × 2 P
ADP
Calvin Cycle P P
ADP
ATP P P
1,3-bisphosphoglyceric acid
Series of 7 Carbon
and 5 Carbon
intermediates P H P
NADPH × 2 H P
NADP P
Glyceraldehyde-3
phosphate
Glucose
Fructose intermediates