Chapter 5 Metabolism

3 Questions About Microbial Metabolism How do microbes metabolize glucose? How do microbes generate ATP? How do microbes get around abnormal conditions?

3 Ways to Metabolize Glucose Glycolysis Pentose Phosphate Entner-Doudoroff Pathway.

Glycolysis (Embden Meyerhof) Major route to pyruvate (sweet loosening) Has 6 C stage and 3 C stage net 2 ATP’s (substrate level phos.) Pathway p. 138 (transparency).

Functions of Glycolysis Major route of hexoses to pyruvate Provides 6/12 critical intermediates Generates energy.

Limitations of Glycolysis Still need 5 carbon sugars (DNA, RNA) Erythrose - 4 Phosphate needed for aromatic amino acids Need NADPH.

Don’t Worry Be Happy! Solution for Most Microbes is Pentose Phosphate Pathway

Pentose Phosphate Pathway - Hexose Monophosphate Shunt Can occur aerobically or anaerobically Two enzymes critical transketolase: transfers 2-carbon molecules transaldolase: transfers 3-carbon molecules Pathway p. 140 (transparency).

Functions of Pentose Phosphate Generates NADPH Generates 4 and 5-carbon sugars Ribose 5 Phosphate Intermediates used to make ATP.

Entner - Doudoroff Pathway Alternative to Pentose P. & Glycolysis Provides 5/12 critical metabolites Pathway p. 174 (transparency) Found in Pseudomonas, Rhizobium, Azotobacter, Enterococcus.

Glycolysis vs. Entner Doudoroff Both convert glucose to two molecules of pyruvate In ED, one pyruvate from top half, other from G3P In glycolysis, both pyruvates arise from G3P. ATP from ED 1/2 of Glycolysis.

Tricarboxylic Acid Cycle (Krebs) Provides remaining intermediates Generates energy NADH & FADH2 Found in all aerobes & most anaerobes Amphibolic Pathway p. 183 (transparency).

ATP Generation Substrate Level Phosphorylation Photophosphorylation Oxidative Phosphorylation.

Electron Transport Electrons progressively transferred from donors to acceptors Passed from NADH and FADH2 to electron carriers in membrane Ends at terminal electron acceptors -- oxygen.

Electron Transport High potential difference = energy production ET produces proton gradients --- makes ATP.

H2 e- 2H+ Electron Transport

H2 e- 2H+ Electron Transport

H2 e- 2H+ Electron Transport

H2 ATP 2H+ e- Electron Transport

H2 2H+ e- Electron Transport

H2 2H+ e- Electron Transport

H2 2H+ ATP e- O2 Electron Transport H2O

Oxidative Phosphorylation Production of ATP at expense of proton motive force from ET.

Fermentation Without O2, NADH not oxidized by ET NADH (glycolysis) must be oxidized Some use pyruvate as terminal electron acceptor Organic molecules are terminal electron acceptors.

Fermentation Types

Anaerobic Respiration Terminal electron acceptors inorganic - nitrate, sulfate, carbon dioxide Not as efficient at ATP synthesis as aerobic.

Anaerobic Respiration Types Dissimilatory Nitrate Reduction: nitrate reduced to nitrite Denitrification: nitrate reduced to nitrogen gas (Pseudomonas, Bacillus) Sulfate Reduction: sulfate reduced to sulfide (Desulfovibrio) Methanogenesis: carbon dioxide converted to methane.

Microbes for Sale!