1Definitions

• Substrate level phosphorylation– Chemical reaction coupled to ATP synthesis– Example: Pyruvate synthesis in glycolysis

• Oxidative (respiratory) phosphorylation– Pumping of protons powered by electron transport with

oxygen as terminal electron acceptor yields ATP

• Photophosphorylation– Pumping of protons powered by absorption of light.

• Respiration: – a redox process in which electrons are passed along an

electron transport chain.

2Central Metabolism:Funneling all nutrients into central pathways

•Many other molecules besides glucose can serve as a source of energy.

3Central Metabolism:A source of building blocks for biosynthesis

BUT, these molecules can’t be broken down to CO2

for energy AND used for biosynthesis

4Other 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

Other ways to make ATP-2

• 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

5

http://dwb.unl.edu/Teacher/NSF/C11/C11Links/www.bact.wisc.edu/microtextbook/metabolism/images/NitrificationET.jpg

6Anaerobic 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).

7What’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.

8Why fermentation-2

9Fermentation: “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.

10Examples 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

11Lessons 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.)

12Anaerobic respiration• Not the same as fermentation

– Respiration involves the electron transport chain and ATP synthesis by chemiosmosis.

– Most general biologists misapply the term.

• 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.

13Anaerobic respiration-2

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

14Anaerobic 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.

Anaerobic bacteria use incomplete citric acid cycle for production of biosynthetic precursors. They do not contain α-ketoglutarate dehydrogenase.

cronus.uwindsor.ca/.../7a371e9af805f74e85256a4f00538021/$FILE/Citric%20acid%20cycle.ppt

16Bacteria 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!