Question

You are working with three mutant strains of yeast. One mutant lacks glyceraldehyde-3-phosphate dehydrogenase, one lacks alcohol dehydrogenase, and the third lacks pyruvate dehydrogenase.

One of the three mutant strains above is able to grow on glucose under both anaerobic and aerobic conditions, although it grows somewhat slower than the wild type (normal) strain under aerobic conditions. Which strain is this? Explain your reasoning.

Answer 1

If glyceraldehyde-3-phosphate dehydrogenase is mutated the yeast can not grow because of defective glycolysis. If alcohol dehydrogenase is absent yeast can not grow under anaerobic conditions because under anaerobic conditions fermentation occurs to make ATP and alcohol dehydrogenase is main enzyme in fermentation.

If pyruvate dehydrogenase is absent and even though oxygen is present yeast will do fermentation (under both aerobic and anaerobic condition)  to make ATP because due to absence of pyruvate dehydrogenase it can not make ATP by oxidative phosphorylation. So yeast lacking pyruvate dehydrogenase will grow in both aerobic and anaerobic conditions.