An overview of bacterial catabolism. Model compound: glucose, C 6 H 12 O 6 Aerobic metabolism With oxygen gas (O 2 ) Fermentation and anaerobic respiration – later Four major pathways Glycolysis, Krebs cycle, electron transport, and chemiosmosis
Glucose, showing numbering system.
EMP = Embden- Meyerhof-Parnas pathwayTraditional glycolysis, yields 2 ATP plus 2 pyruvic acids.
Pentose PhosphateComplicated pathway, produces 5 carbon sugars and NADPH for use in biosynthesis.
Entner-DoudoroffYields only 1 ATP per glucose, but only used by aerobes such as Pseudomonas which make many ATP through aerobic respiration.
Usually used in addition to EMP or Entner-Doudoroff.
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.
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.
Electrons are passed carrier to carrier, releasing energy.
Process can’t continue without an electron acceptor at the end. In aerobic metabolism, the acceptor is molecular oxygen.
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.
Electrochemical gradient establishes a voltage across the membrane. Flow of protons (instead of electrons) does work (the synthesis of ATP).