1. Other ways to make ATP Photosynthesis: light driven ATP synthesis.
Oxygenic (photosystem I and II)
Uses chlorophyll, produces oxygen from water
Anoxygenic (photosystem I only)
H’s to reduce CO2 from other sources
Inorganic molecules can be oxidized producing ATP synthesis by e- transport and chemiosmosis.
Examples: Fe+2 to Fe+3, NH3 to NO2-
Requires O2 as terminal electron acceptor

2. Anaerobic metabolism to make ATP
Anaerobic respiration: organic compounds oxidized, electrons passed down e- transport chain to some molecule other than oxygen (e.g. NO3-, SO4-2).
Just like aerobic respiration but w/o O2
Fermentation: common anaerobic pathway used by many medically important bacteria.
Electron transport not important in ATP production
Organic molecules serve as electron acceptor (sink).

3. What’s Fermentation for?
Glucose can be oxidized to pyruvic acid with the synthesis of 2ATPs. This alone is enough energy to live on. It depends on the oxidation of NADH to NAD so that NAD is available to accept electrons during the oxidation of glucose.

4. Why fermentation-2

5. Fermentation: “life without air”
Without O2 as an e- acceptor, NADH cannot be re-oxidized to NAD.
Even though aerobic metabolism can produce ~36 ATP from 1 glucose, the 2 ATP from glycolysis is enough.
But glycolysis requires that NAD be reduced to NADH; what happens when ALL the NAD becomes NADH with no O2 to accept the H?
Pyruvic acid is reduced, and the product thrown away; NAD restored, glycolysis can be repeated, more ATP made.
A variety of ways of solving this problem exist; many types of molecules can be produced from fermentation.

6. Examples for fermentations
Lactic acid fermentation
Lactic acid
Alcoholic fermentation
Ethanol, carbon dioxide
Mixed acid fermentation
Lactic acid, formic acid, succinic acid, ethanol, H2, CO2
Propionic acid fermentation
propionic acid, acetic acid, and carbon dioxide

7. Lessons from Fermentation
Fermentation is inefficient. If C6H12O6 has lots of energy-rich H’s, so does C3H5O3 (lactic acid); the product cannot be further metabolized and is thrown away! Only a couple of ATPs are made.
Fermentation is quick. Even though few ATPs are made, they are made quickly.
Fermentation is wasteful. Large amounts of substrate (e.g. sugar) is used, making large amounts of product (e.g. lactic acid, ethanol, etc.)

8. Anaerobic respiration
Not the same as fermentation
Respiration involves the electron transport chain and ATP synthesis by chemiosmosis.
Most general biologists are very confused.
Anaerobic means without oxygen
Anaerobic respiration: organic (or inorganic) molecule is oxidized, the removed electrons are sent down the electron transport chain, and something OTHER than oxygen is the electron acceptor.
Carried out by anaerobic bacteria, but some aerobes (growing anaerobically) can reduce forms of N this way.

9. Anaerobic respiration-2
In this example, nitrate is reduced to nitrite. Other examples: sulfate reduced to elemental sulfur (S) or S to sulfide (H2S).

10. Anaerobic respiration-3
Molecules of electron transport chain different
Some “aerobes” and facultative anaerobes carry out anaerobic respiration
A different set of electron carriers produced in response to lack of oxygen, or
Oxygen is preferred electron acceptor; others work if oxygen is not available.
Example: denitrification
NO3- → NO2- → NO → N2O → N2
Important environmentally; fixed nitrogen lost under anaerobic conditions.

11. Bacteria and the fragility of existence
Bacteria use ATP or the proton motive force to:
Move
Synthesis proteins (lots of them)
Transport molecules into the cell
Synthesize cell materials
Homeostasis
Bacteria do not store ATP
Calculations: E. coli has enough ATP to last a few seconds
Thus, cells must keep on making it.
Bacteria carefully regulate their use of energy!