1. II. Energetics, Enzymes and Redox
3.3 Energy/Carbon Source Classes of Microorganisms-definitions
3.4 Bioenergetics
3.6 Electron Donors and Electron Acceptors
3.7 Energy-Rich Compounds: ATP
Modes of ATP Synthesis

2. 3.3 Energy Classes of Microorganisms
Metabolism
The sum total of all of the chemical reactions that occur in a cell
Catabolic reactions (catabolism)
Energy-releasing metabolic reactions
Anabolic reactions (anabolism)
Biosynthetic metabolic reactions

3. Broad Overview of Metabolism
Prokaryotes will not make something if they can import it
There are only a few key precursor molecules (but lots of ways
to make them)
Energy sources vary

4. 3.3 Energy/Carbon Source Classes of Microorganisms
Microorganisms need building blocks plus energy to survive, grow and reproduce.
Carbon is a key component of building blocks (but not the only one):
Imported
Synthesized de novo
Energy can come from different sources

5. 3.3 Energy/Carbon Source Classes of Microorganisms
Microorganisms have a variety of ways to conduct their metabolism
Grouped into carbon source classes
Heterotrophs rely on reduced carbon
Autotrophs fix CO2 aka reduce CO2
Grouped into energy source classes
Chemotrophs use chemical energy
Chemolithotrophs use inorganic compounds
Chemoorganotrophs use carbon compounds
Phototrophs use light energy

6. 3.3 Energy Classes of Microorganisms
Autotrophs may be chemotrophs or phototrophs with respect to energy source
Phototrophic autotrophs (photoautotrophs) are familiar
Cyanobacteria (Sec.14.3)
Photosynthesize using chlorophyll a
Fix CO2 to carbohydrate using Calvin Cycle
Chemotrophic autotrophs (chemoautotrophs) are less familiar
Methanogens (Sec.13.20) = Archaea; sediments, animals
Use CO2 to CH4 with unusual enzymes for energy
Use methanol or acetate from CH4 for carbon

7. 3.3 Energy Classes of Microorganisms
Heterotrophs may be chemotrophs or phototrophs with respect to energy source
Chemotrophic heterotrophs (chemoheterotrophs) are very common
Phototrophic heterotrophs (photoheterotrophs) also exist
Heliobacter (Sec. 14.8) a gram + rod
Carries out photosynthesis using bacteriochlorophyll g
Relies on pyruvate, lactate, butyrate, acetate for carbon

8. 3.4 Bioenergetics
In any chemical reaction, some energy is lost as heat but some energy (Free energy = G): energy released that is available to do work
The change in free energy during a reaction at standard conditions is referred to as ΔG0′
ΔG: free energy that occurs under actual conditions in a cell
Microbes use free energy to drive metabolism

9. 3.4 Bioenergetics
Microbes derive free energy from light (phototrophs) or chemicals (chemotrophs)
They use the free energy to power anabolism
The most productive way (but not the only way) to obtain free energy is by moving electrons around
oxidation/reduction or redox reactions

10. 3.6 Electron Donors and Electron Acceptors
Energy from oxidation–reduction (redox) reactions is used in synthesis of energy-rich compounds (e.g., ATP)
Redox reactions occur in pairs (two half reactions; Figure 3.8)
Electron donor: the substance oxidized in a redox reaction (loses electrons)
Electron acceptor: the substance reduced in a redox reaction (gains electrons)

11. 3.6 Electron Donors and Electron Acceptors
Half reaction donating e–
Electron
donor
Electron
acceptor
Formation
of water
Net reaction
Half reaction accepting e–
Figure 3.8 Example of an oxidation–reduction reaction.
Energy from oxidation–reduction (redox) reactions is used in synthesis of energy-rich compounds (e.g., ATP)
Figure 3.8

12. 3.6 Electron Donors and Electron Acceptors
Reduction potential (E0′): measurement of energy transfer in redox reactions or tendency to donate electrons
Expressed as volts (V)
Half reactions with highly positive reduction potentials occur easily
Reduced substance with a more negative E0′ donates electrons to the oxidized substance with a more positive E0′

13. 3.6 Electron Donors and Electron Acceptors
The redox tower represents the range of possible reduction potentials (Figure 3.9)
The reduced substance nearer the top of the tower donates electrons
The oxidized substance nearer the bottom of the tower accepts electrons
The farther the electrons "drop," the greater the amount of energy released

14. Figure 3.9 The redox tower.
Figure 3.9

15. 3.6 Electron Donors and Electron Acceptors
Redox reactions usually involve reactions between intermediates (carriers)
Electron carriers are divided into two classes
Prosthetic groups (attached to enzymes)
Example: heme
Coenzymes (diffusible)
Examples: NAD+, NADP

16. 3.7 Energy-Rich Compounds
Chemical energy released in redox reactions is primarily stored in certain phosphorylated compounds (Figure 3.12)
ATP; the prime energy currency
Phosphoenolpyruvate
Glucose 6-phosphate and Acetyl phosphate
Chemical energy also stored in coenzyme A, a high energy sulfur compound

17. Anhydride bonds
Ester bond
Ester bond
Anhydride bond
Phosphoenolpyruvate
Adenosine triphosphate (ATP)
Glucose 6-phosphate
Compound
G0′kJ/mol
Thioester
bond
Anhydride bond
ΔG0′< 30kJ
Phosphoenolpyruvate
–51.6
1,3-Bisphosphoglycerate
–52.0
Acetyl phosphate
–44.8
Figure Phosphate bonds in compounds that conserve energy in bacterial metabolism.
ATP
–31.8
ADP
–31.8
Acetyl
Coenzyme A
Acetyl phosphate
Acetyl-CoA
–35.7
Acetyl-CoA
ΔG0′< 30kJ
AMP
–14.2
Glucose 6-phosphate
–13.8
Figure 3.12

18. 3.7 Energy-Rich Compounds-Long Term
Long-term energy storage involves insoluble polymers that can be oxidized to generate ATP
Examples in prokaryotes
Glycogen
Poly-β-hydroxybutyrate and other polyhydroxyalkanoates
Elemental sulfur
Examples in eukaryotes
Starch
Lipids (simple fats)

19. 3.7 Energy-Rich Compounds
A special energy rich compound that also serves as an electron carrier
Reduced NAD carries high energy electrons
Provides “reducing power” for biosynthesis

20. Modes of ATP Synthesis Substrate level phosphorylation
Transmembrane gradient (eg proton gradient or pmf)
Respiration
Aerobic
Anaerobic
Photosynthesis
Anoxygenic
Oxygenic

21. Direct transfer of high energy phosphate

22. Example: pyruvate kinase reaction
Part of catabolic pathway called glycolysis or EMP pathway
PEP is a product of another reaction
Substrate level phosphorylations are common in all organisms

23. Metabolic pathways that use a gradient to make ATP Respiration
Aerobic-use oxygen as final electron acceptor
Anaerobic-use something other than oxygen as final acceptor
Photosynthesis
Anoxygenic-use something other than water as original electron donor
Oxygenic-use water as original electron donor

24. Microbes use transmembrane gradients as a source of energy to make ATP.
QUESTION: How do they set up the gradients?
ANSWER: They use energy released in redox reactions to set up a transmembrane gradient.

25. Setting Up a Transmembrane gradient
Figure 3.20 Generation of the proton motive force during aerobic respiration.
Top of tower
Bottom of tower
Figure 3.20

26. MICROBES CAN USE MANY OTHER SUBSTANCES AS DONORS OR ACCEPTORS!!!!!!
Fig shows NADH as the electron donor
And oxygen as the electron acceptor
But………….
MICROBES CAN USE MANY OTHER SUBSTANCES AS DONORS OR ACCEPTORS!!!!!!

27. MICROBES CAN USE MANY OTHER SUBSTANCES TO SET UP THE GRADIENT!!!!!!
Fig shows a gradient in the form of an H+ gradient
But………….
MICROBES CAN USE MANY OTHER SUBSTANCES TO SET UP THE GRADIENT!!!!!!

28. ATP Synthase aka F1F0 Synthase or ATPase
Controlled entry of protons drives ATP synthesis
3-4 protons/ATP
Can work in reverse

29. Anaerobic respiration
Nitrate (NO3–), ferric iron (Fe3+), sulfate (SO42–), carbonate (CO32–), fumarate, DMSO are examples of acceptors
Less energy released compared to aerobic respiration
“Primitive” form of respiration?

30. Figure 13.39
Figure Major forms of anaerobic respiration.
Figure 13.39

31. Nitrate Reduction is a Good Example of Anaerobic Respiration (Ch. 13
Nitrate Reduction is a Good Example of Anaerobic Respiration (Ch and 13.17)
Nitrate Reduction = use of nitrate as electron acceptor in anaerobic respiration (nitrate to nitrite)
A dissimilative process
Conversion of nitrate to more reduced substances such as N2O or N2 = denitrification

32. Figure 13.40 (Escherichia coli) stutzeri) Nitrate reduction
Nitrate reductase
Nitrite reductase
Denitrification (Pseudomonas
stutzeri)
Nitric oxide reductase
Figure Steps in the dissimilative reduction of nitrate.
Gases
Nitrous oxide reductase
Figure 13.40

33. Figure 13.41 Respiration and nitrate-based anaerobic respiration.

34. Lithotroph: type of chemotroph that uses inorganic substance (e. g
Lithotroph: type of chemotroph that uses inorganic substance (e.g. a mineral) as a source of energy: in other words as an electron donor.
Anaerobic respiration: process in which electrons are transferred to a final acceptor that is not oxygen-can be organic or inorganic

35. Photosynthesis
Uses light energy to remove an electron from an electron donor and boost it to a high energy level
Photons captured by pigment molecules
Chlorophylls, bacteriochlorophylls, accessory pigments such as carotenoids
Absorb different wavelengths

36. Photosynthesis-Anoxygenic
Anoxygenic photosynthesis uses an electron donor other than water
H2S is a common donor
Green sulfur bacteria, purple bacteria, Heliobacter, some Archaea
Use a transmembrane gradient to generate ATP via cyclic photophosphorylation

38. Photosynthesis-Oxygenic
Oxygenic photosynthesis uses water as electron donor
Cyanobacteria
2 Photosystems linked by electron carriers
Use a transmembrane gradient to generate ATP via either cyclic photophosphorylation or noncyclic photophosphorylation

39. Makes reducing power in the form of NADPH
When reducing power is not needed-cyclic
photophosphorylation

40. III. Fermentation and Respiration Overview
3.8 Glycolysis
3.9 Fermentative Diversity and the Respiratory Option
3.10 Respiration: Electron Carriers
3.11 Respiration: The Proton Motive Force
3.12 Respiration: Citric Acid and Glyoxylate Cycle
3.13 Catabolic Diversity