Practice problems.....Asignment 3

1. In a biosynthetic pathway, A to E are intermediate metabolites and final product is G. Several mutants are isolated that are defective in one or the other step in the pathway. The order in which these intermediates are formed is not known. Each intermediate is tested for its ability to support the growth to each mutant (1 to 5). In the following table, + indicates growth and – indicates no growth.

A)What is the order of A to E in the pathway?
B) At which point in the pathway is each mutant blocked?
[ hint: approach followed by Tatum and Beadle with Neurospora arg- auxotrophs]

2. Two mutants at the tryptophan locus, trpA- and trpB-, are known to be close to a cysteine locus (cys). A bacterial strain of genotype cys+trpA-is conjugated to a donor strain that transfers cys-trpB-. The reciprocal cross in which donor transfers cys+trpA-to the strain that is cys-trpB-. In both the cases, the numbers of prototrophic recombinants are comparable. Determine the order of tryptophan loci relative to cysteine locus.