Response To Questions From Part A To B Six mutants are isolated, all of which re

Question

Response To Questions From Part A To B Six mutants are isolated, all of which require compound G for growth. The compounds A-E in the biosynthetic pathway to G are known, but their order in the pathway is not known. Each compound is tested for its ability to support the growth of each of the mutants (#1-6). In the following table, a plus sign indicates growth and a zero indicates no growth MUTANT COMPOUND TESTED a) Draw the order of compounds in the biochemical pathway and indicate where each mutant is blocked. Explain how you derived your pathway using the data in the table. what compound does Mutant #3 accumulate? Explain your reasoning.++ b)

Explanation / Answer

a) A particular compound will support growth if it is later in the pathway than the enzymatic step blocked in the mutant. We can rephrase it saying that the more mutants a compound supports, the later in the pathway growth would be. In the given table, compound G supports growth of all mutants and can be considered the end product of the pathway, however compound D does not support the growth of any compound except mutant 5, therefore it should be the least supportive compound to the mutants growth; hence the starting substrate of the pathway. The data indicate the gradually increasing order of support for more number of substrates starting from D that supports one mutant for growth, A that supports 2 mutants for growth, C that supports 3 mutants to grow, B that supports 4 mutants to grow, E that supports five mutants to grow and finally G that remains at the end of the pathway by supporting growth of all six mutants.

Now, the data also suggest that, if a mutant can grow only in presence of G, then the spot where this mutant would be blocked will remain just before the G substrate in the biosynthetic pathway. Therefore, mutant 2 will be blocked before G, in between G and E, mutant 6 will be blocked before E, in between E and B and so on. The biosynthetic pathway from the data can be constructed as stated below where the vertical lines in between arrows would indicate the step where each mutant is blocked.

----I----> D ----I----> A ----I----> C ----I----> B ----I----> E ----I----> G

5 1 4 3 6 2

b) Mutant #3 will tend to accumulate compounds C, A and D as it could not grow or utilize these three compounds. Mutant #3 can utililize or degrade substrates B, E and G therefore it will not accumulate those three compounds.

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