Question

2. Four auxotrophic mutants in Neurospora crassa.(common bread mold) will grow if arginine is added to minimal medium. Some of these mutants will also grow if other chemicals in the arginine anabolic pathway are added to minimal medium. The growth pattems are show in the table (+ = growth and 0 - no growth) Metabolites added to minimal medium Glutamic Semialdehyde Arginine Mutants Precursor Citrulling . Omithing A. What is the order of metabolites in the pathway? B. Indicate with a number over the arrows where each mutant is blocked in the pathway?

Answer 1

Precursor, Glutamic semialdehyde, Ornithine, Citrulline, Arginine

Mutant 1 grows only in the presence of arginine. It means arginine is the last molecule of the pathway. This is because the mutant is able to synthesise all the other molecules and therefore their presence is not affecting the growth of the mutant. But the mutant is growing solely in the presence of arginine, hence arginine will be the last molecule of the pathway.

Mutant 2 is growing in the presence of both are arginine and citrulline. And arginine is the last molecule of the pathway, so citrulline in will be the second last.

Mutant 4 is growing in the presence of arginine, citrulline and ornithine. So, ornithine will be the third last molecule. And the one which is left glutamic semialdehyde will be the second molecule of the pathway.

Precursor will always be the first moelcule.

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