Question

Following the oxidation of glucose in glycolysis, describe how an E. coli cell under aerobic conditions would regenerate NAD+. Also, for each organism briefly describe how ATP is produced under the indicated conditions by listing the pathways used and the mechanism of ATP synthesis.

Answer 1

Glucose fermentation by E. coli proceeds in two stages

In the first stage, glucose is metabolized to pyruvate via the glycolysis pathway reactions. which result in generating 2 molecules of NADH and 4 molecules of ATP. Since 2 ATP are needed in the early steps of the pathway, a total of 2 ATP are produced for each glucose molecule consumed.

In the second stage the 2 NADH molecules generated by the glycolysis pathway must be re-oxidized to NAD⁺ to support subsequent rounds of glucose metabolism by the cell. These NADH oxidation steps are accomplished by reducing several of the intermediates (e.g., pyruvate or a product derived from it). This results in the formation of one or more of the “mixed acid” fermentation products.

The ATP is generated by substrate level phosphorylation (SLP) reactions using suitable glycolysis pathway intermediates to donate a phosphate group to ADP.