You are studying a type of yeast that can grow in both the presence and absence

Question

You are studying a type of yeast that can grow in both the presence and absence of oxygen using normal metabolic pathways (glycolysis, Krebs cycle, ETS, ATP synthase). You have generated a mutant that grows well in the presence of oxygen, but not in its absence. You do a stude where you look at the relative levels of NADH in both the mutant and wild-type yeast in the presence and absence of oxygen, and you get the following data:

Identify one metabolic enzyme that would account for the increased levels of NADH observed in the mutant yeast in the absence of oxygen, and explain why a mutation in the enzyme would cause the observed results.

Explanation / Answer

In the presence of oxygen NADH levels are almost same in wild type and mutant yeast. It indicates enzymes of aerobic pathways are not mutated.

Under anaerobic conditions yeast cell will undergo lactate fermentation. pyruvate (product of glycolysis) is converted in lactate in presence of enzyme Lactate dehydrogenase using NADH. During this reaction lactate and NAD+ are generated. These NAD+ are utilized in glycolysis. Without NAD+ glycolysis cannot occur. When Enzyme Lactate dehydrogenase is mutated NADH will not be utilized for producing lactate so it will get accumulated inside cell also NAD+ is not available for glycolysis so cell will not be able to grow.

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