6 5 points Feeding experiment and biochemical pathway a From

6. (5 points) Feeding experiment and biochemical pathway. a) From a mutagenesis screen, five mutants (named c9, c10, cl4, c18, c21) were identified and they each were found to mutate a different gene. Feeding experiments were done by growing each mutant on minimal medium supplemented by four different known precursors of cytosine (A-D). The results are summarized in the table growth; no growth) Precursor/ product Mutant A B C D Cytosine C10 c14 c18 c21 Show a simple linear biochemical pathway of the four precursors and the end product (cytosine). Indicate which step is blocked by each of the five mutations.

Solution

1. The linear pathway is as follows:

^c18__D__^c14 B__^c9A__ ^c10C__ ^c21Cytosine

2. At C9 and c10, precursor B would accumulate as double mutant.

At C10 and C14, precursor D will accumulate as double mutant.