Question

Scientists can use mutants to study metabolic pathways. These organisms have a mutation in a gene encoding a metabolic pathway enzyme that results in the activation of that enzyme. Saccharomyces cerevisiae (a yeast species) mutants are available that grow on pyruvate or ethanol, but not sugars or glycerol. Which of the following glycolytic enzymes is most likely affected?

1. triose phosphate isomerase

2. aldolase -phophoglucose isomerase (phosphohexose isomerase or glucose-6-phosphate isomerase)

3. hexokinase

4. pyruvate kinase

Answer 1

The yeast mutants likely have a mutation in the gene encoding pyruvate kinase, the last enzyme in glycolysis, affecting their ability to metabolize sugars while still allowing growth on pyruvate or ethanol.

Step-by-step explanation:

Based on the information provided, the Saccharomyces cerevisiae (a yeast species) mutants that grow on pyruvate or ethanol but not sugars or glycerol are likely to have a mutation in the gene encoding pyruvate kinase. Pyruvate kinase is the last enzyme in the glycolytic pathway, responsible for converting phosphoenolpyruvate (PEP) to pyruvate, so a mutation causing its inactivation would impair the yeast cell's ability to utilize sugars such as glucose but still allow for the use of pyruvate and ethanol which enter the metabolic pathways downstream. Furthermore, a complete lack of pyruvate kinase activity is usually lethal; however, these mutants are viable, indicating that the mutations may lead to reduced, rather than completely abolished, enzyme function.