6. (5 points) Feeding experiment and biochemical pathway. a) From a mutagenesis

Question

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.

Explanation / Answer

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.

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