1. An overview of bacterial catabolism
Model compound: glucose, C6H12O6
Aerobic metabolism
With oxygen gas (O2)
Fermentation and anaerobic respiration – later
Four major pathways
Glycolysis, Krebs cycle, electron transport, and chemiosmosis
The Goal: gradually release the energy in the glucose molecule and use it to make ATP.
The carbons of glucose will be oxidized to CO2.

2. Fructose: same atoms, but rearranged.
Glucose, showing numbering system.

3. Glycolysis: glucose is broken
Glucose is activated
Glucose Glu-6-P
2 ATPs are “invested”
Glu (6 C’s) broken into two 3-C pieces
2 oxidations steps
NAD NADH
4 ATPs are produced, net gain: 2 ATPs
2 molecules of pyruvic acid are produced.

4. 3 ways bacteria use glucose
EMP = Embden- Meyerhof-Parnas pathway Traditional glycolysis, yields 2 ATP plus 2 pyruvic acids.
Pentose Phosphate Complicated pathway, produces 5 carbon sugars and NADPH for use in biosynthesis.
Entner-Doudoroff Yields only 1 ATP per glucose, but only used by aerobes such as Pseudomonas which make many ATP through aerobic respiration.

5. Usually used in addition to EMP or Entner-Doudoroff.

6. Krebs Cycle detailed

7. What happens: carbons of glucose oxidized completely to CO2
Preliminary step: pyruvic acid oxidized to acetyl-CoA.
Things to note: several redox steps make NADH, FADH2
One ATP made
OAA remade, allowing cycle to go around again.

8. About Coenzyme A
The vitamin CoA is way bigger than the organic acids acted on by the enzymes. CoA serves as a handle; an acid attaches to it, chemistry is done on the acid.
Acids (e.g. acetate, succinate) attach to this –SH group here.
This piece here = acetyl group.
coenzymes.htm

9. Electron transport Metabolism to this point, per molecule of glucose:
2 NADH made during glycolysis, 8 more through the end of Krebs Cycle (plus 2 FADH2)
What next?
If reduced NAD molecules are “poker chips”, they contain energy which needs to be “cashed in” to make ATP.
In order for glycolysis and Krebs Cycle to continue, NAD that gets reduced to NADH must get re-oxidized to NAD.
What is the greediest electron hog we know? Molecular oxygen.
In Electron transport, electrons are passed to oxygen so that these metabolic processes can continue with more glucose.
Electron carriers in membrane are reversibly reduced, then re-oxidized as they pass electrons (or Hs) to the next carrier.

10. About Hydrogens A hydrogen atom is one proton and one electron.
In biological redox reactions, electrons are often accompanied by protons (e.g. dehydrogenations)
In understanding metabolism, we are not only concerned with electrons but also protons.
Also called hydrogen ions or H+
H+ (hydrogen ions) and electrons are opposites!! Don’t get them confused!

11. Electron transport
Electrons are passed carrier to carrier, releasing energy.
All occurs at the cell membrane
NADH is oxidized to NAD
H’s are passed to next electron carrier; NAD goes, picks up more H.
Process can’t continue without an electron acceptor at the end. In aerobic metabolism, the acceptor is molecular oxygen.

12. Electron Transport molecules
Protein?
Cofactor
Carry H?
Flavoproteins
Yes
Flavins
yes
Quinones No
Small lipids NA
Iron-Sulfur proteins
Fe-S groups no
Cytochromes
Heme (Fe)

13. Chemiosmosis: electron transport used to make ATP
Energy released during
electron transport used
to “pump” protons
(against the gradient) to the outside of the membrane.
The membrane acts as an insulator;
protons can only pass through via
the ATPase enzyme; the energy
released is used to power synthesis
of ATP from ADP and Pi.
Creates a proton current (pmf) much like the current of electrons that runs a battery.

14. Proton motive force
Electrochemical gradient establishes a voltage across the membrane. Flow of protons (instead of electrons) does work (the synthesis of ATP).

15. Overview of aerobic metabolism
Energy is in the C-H bonds of glucose.
Oxidation of glucose (stripping of H from C atoms) produces CO2 and reduced NAD (NADH)
Energy now in the form of NADH (“poker chips”)
Electrons (H atoms) given up by NADH at the membrane, energy released slowly during e- transport and used to establish a proton (H+) gradient across the membrane
Energy now in the form of a proton gradient which can do work.
Electrons combine with oxygen to produce water, take e- away.
Proton gradient used to make ATP
Energy now in the form of ATP. Task is completed!

16. Definitions 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.

17. Central Metabolism: Funneling all nutrients into central pathways
Many other molecules besides glucose can serve as a source of carbon.

18. Central Metabolism: A source of building blocks for biosynthesis
BUT, these molecules can’t be broken down to CO2 for energy AND used for biosynthesis