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 study 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.

A) Explain why there are normal levels of NADH in the wild type yeast and the mutant yeast in the presence of oxygen (blue bars).

B) Explain why there are normal levels of NADH in the wild type yeast, but higher levels of NADH in the mutant yeast in the absence of oxygen (red bars).

C) Identify a metabolic enzyme that would account for the results shown above if it were mutated. Explain on a molecular level, in no more than 3 sentences, HOW it would cause the results shown in its mutated state.

Explanation / Answer

A) In the presence of oxygen the metabolic conditions (glycolysis, Krebs cycle, ETC, ATP synthesis) of both mutant and wild types strains are same and operate equivalently. This is because both strains have the ability to grow under aerobic conditions. Hence, both strains have same NADH levels.

B) In the absence of the oxygen normal levels of NADH in the wild type yeast are observed, because it can operate glycolysis, Krebs cycle, ETC both in aerobic and anaerobic conditions. But the mutant strains cannot grow well in the absence of oxygen, so the NADH, which is generated in the glycolysis and Krebs cycle are not used by ATP synthase. Hence, they left over and accumulated in the cell.

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