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Unformatted text preview: grew only on arg - neither cit nor orn could substitute
• What can we deduce about the biochemical pathway these mutants
affect? Genetic Analysis of
Biochemical Pathways • Hypothesis: Each mutation creates a “block” in a biosynthetic
pathway by inactivating an enzyme in that pathway
• If we supplement with a substance that is after the block, the other
(wildtype) enzymes can complete the pathway
• What is the ﬁnal product of the pathway? Genetic Analysis of
Biochemical Pathways • Since all mutant strains can grow w/arg supplementation, arg is
AFTER all of the blocks in the pathway.
• Some mutants will grow with cit, but not orn
• In these mutants, the block is after orn, but before cit
• Some mutants will grow with any of the three supplements
• In these strains, the block is before any of the three compounds Genetic Analysis of Biochemical
Pathways • Next: where in the pathway do the genes function?
• arg1 is required to convert cit to arg
• arg2 and 3 are required to convert orn to cit
• arg4-7 are are required before orn So: Precursor(s) arg4-7 ornithine arg...
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