Question

6. A yeast variant was discovered that had a shorter glycolytic pathway. This "mutant" yeast made a novel enzyme that catalyzed the following reaction: Glyceraldehyde-3-phosphate + H2 + NAD → 3-phosphoglycerate + NADH+H* A. Would you expect this novel yeast strain to grow well under anaerobic conditions using glucose as a carbon source? Explain. B. Would you expect this novel yeast strain to grow well under aerobic conditions using glucose as a carbon source? Explain.

Answer 1

6. A) No, this strain will not grow well in anaerobic condition using glucose as a carbon source.

In normal glycolytic pathway, glyceraldehyde-3-phosphate converts to 1,3-bisphosphoglycerate (1,3-BPG) and 1,3-BPG is converted to 3-phosphoglycerate (3-PG). During the conversion of 1,3-BPG to 3-PG one ATP is generated. So, for one molecule of glucose, in this step, 2 ATP is generated which gives a cumulative ATP yield in the anaerobic glycolytic pathway of 2 ATP.

Now, the conversion of 1,3-BPG to 3-PG step is avoided due to the novel enzyme. So, the net yield of ATP from the anaerobic glycolytic pathway will be zero. As the yeast is in anaerobic environment, it will not be able to synthesize ATP by oxidizing NADH by oxidative phosphorylation. Due to a lack of energy currency, ATP, the cell will not survive.

B) Yes, it will grow.

Though the net production of ATP from the glycolytic pathway is zero, it still can metabolize the pyruvate formed, in the TCA cycle and produced NADH will be oxidized in oxidative phosphorylation and ATP will be generated.