Name: 23. Baker\'s yeast (Saccharomyces cerevisiae) can synthesize the essential

Question

Name: 23. Baker's yeast (Saccharomyces cerevisiae) can synthesize the essential amino acid methionine. After chemical mutagenesis, six haploid auxotrophic mutants were isolated that required methionine supplementation to the mineral salts medium that supports growth of th e wild type parent. Some of the mutants, however, could also grow on media supplemented with one or more of the compounds shown in Table 1 Table 1. Growth of mutants on indicated compound Cystathionine None Supplement: Methionine Cysteine Homocysteine Mutant Strain A. Write a biochemical pathway for methionine synthesis involving these compounds, consistent with these results. Assign each mutation to a step in the pathway B. Mutants 2, 5, and 6 were interbred to produce diploid F1 hybrids. Some of the resulting diploids could grow on cysteine; others could not (Table 2). What does this reveal about the mutations in strains 2, 5, and 6 and about the minimum number of genes needed for biosynthesis of methionine? Table 2. Growth on cysteine of diploids made from indicated haploid parents wt 2 6 wt

Explanation / Answer

The interpretation can be made as follows:

The interbreeding gave the following results:

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