Consider the pathway for the synthesis of the amino acid arginine in Neurospora

Question

Consider the pathway for the synthesis of the amino acid arginine in Neurospora:

                    ARG-E                      ARG-F                            ARG-H

ornithine -------------> citrulline -----------> arginosuccinate --------> arginine

Mutant strains 1,2 and 3 are unable to synthesize arginine. When grown in minimal media supplemented with the following compounds, they exhibit growth as shown below (growth is shown by + and no growth is shown by o).

Which gene are each of the mutants defective in? Be sure to determine all three mutants in your answer.

Explanation / Answer

F___ mutant 1 ______E____ mutant 2 ____H___ mutant 3

The product of the gene ARG-E converts ornithine to citrulline, so supplementing an ARG-E mutant with citrulline or arginosuccinate will allow that strain to make arginine,but supplementing with ornithine won't allow it to. Similarly, an ARG-F mutant requires arginosuccinate supplementation to make arginine, and an ARG-H mutant won't be ableto make arginine no matter which of these compounds it is supplemented with

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