Question

3. A number of different mutant yeast strains were isolated (1-5), all of which needed compound G for survival. While the precursors to G are known (compounds A-E), investigators did not know their order in the pathway. To determine this, each compound was tested for its ability to support growth for each mutant. The results of this experiment are shown below. A “+” sign indicates that the chemical was able support growth, but a “–“ indicates that it was not able to support growth.

            A         B         C         D         E          G

1          -           -           -           +          -           +

2          -           +          -           +          -           +

3          -           -           -           -           -           +

4          -           +          +          +          -           +

5          +          +          +          +          -           +

Determine the order of compounds in the pathway, and at which point each mutant is blocked.

Answer 1

In the first mutant, only D was sufficient to induce growth which means that it was the last molecule that was required to make G.

In mutant 2 - when we supply B and D, mutant yeast was able to grow. which means that B is the precursor for D

In mutant 4 when we supply B, C and D, mutant yeast was able to grow. which means that C is the precursor for B

In mutant 5 when we supply A, B, C and D, mutant yeast was able to grow. which means that A is the precursor for C