Consider the pathway for the synthesis of the amino acid arginine in Neurospora
ID: 206246 • Letter: C
Question
Consider the pathway for the synthesis of the amino acid arginine in Neurospora:
ARG-E ARG-F ARG-H
ornithine-------citrulline---- argininosuccinate ----arginine
Mutant strains of Neurospora are grown in minimal media supplements as follows. Each mutant strain carries only a single mutation. Growth is shown by (+) and no growth is shown by (-).
Supplements
Mutant strain minimal ornithine citrulline argininosuccinate arginine
A - - - + +
B - - + + +
C - - - - +
Pair each mutant strain with the correct gene in the pathway.
Explanation / Answer
In the given case, mutant B can grow in the presence of citrulline and other upstream metabolites. So, it must contain a mutation in enzymes that synthesize metabolites upstream to citrulline. There is only one enzyme that catalyzes the upstream reaction of ornithine to citrulline. So, mutant B must be ARG-E.
Similarly, mutant C can grow in the presence of argininosuccinate and other upstream metabolites. So, it must contain a mutation in enzymes that synthesize metabolites upstream to argininosuccinate. There are two enzymes that catalyze the upstream reactions. One is ARG-E which catalyzes the conversion of ornithine to citrulline and the other enzyme is ARG-F which catalyzes the conversion of citrulline to argininosuccinate. We know that mutant B is ARG-E. So, mutant A ARG-F.
The remaining mutant is mutant C = ARG-H
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