Consider the following trp operon mutants. The trpR- mutation produces a repress
ID: 11514 • Letter: C
Question
Consider the following trp operon mutants. The trpR- mutation produces a repressor that cannot bind tryptophan; the trpO- mutation produces an operator that cannot be bound by the wild type repressor/trp complex; the trpa- mutation cannot form the attenuator; the trpE- mutation cannot produce an active biosynthetic enzyme. Can these strains synthesize tryptophan if tryptophan is present in the cell? Justify your answer.a. F' trpR+ trpa- trpO- trpE+ / trpR+ trpa+ trpO+ trpE-
b. F' trpR- trpa+ trpO+ trpE+ / trpR+ trpa- trpOc trpE-
c. F' trpR- trpa- trpO+ trpE+ / trpR- trpa+ trpO- trpE+
Explanation / Answer
Tryptophan is an essential amino acid in bacteria, so the trp operon is constantly working unless there is an abundant amount in the environment. The wild type trp operon codes for an inactive repressor which is activated by large amounts of tryptophan. The active repressor binds to the operator to stop synthesizing tryptophan. The attenuator regulatory sequence creates a hairpin when there is a lot of tryptophan to stop the ribosome from translating the sequence. The biosynthetic enzyme in this situation would be RNA polymerase. With this information, it is discovered that trpR-, trpa-, trpO-, and trpE- all prevent the trp operon from being STOPPED when there is HIGH amounts of tryptophan.
So assuming that there are two alleles of each gene in question, with the "+" designating the dominant, wild type sequence, and "-" of course designating the mutant, we can begin analyzing each strain.
For "a", it seems as if everything is normal in letter, so the answer is that the strain would not be able to produce tryptophan if tryptophan is present.
For "b," you wrote a "c" instead of a plus or minus, but according to my logic, it shouldn't matter, because the answer should be the same as "b."
For "c," the only mutant is trpR-. This would prevent the repressor from being activated, and RNA polymerase would still try to translate the operon. However, the attenuator of trpa+ would make sure that the synthesis of tryptophan would stop, so overall the strain would not be able to produce tryptophan if tryptophan is present.
I'm not sure whether this answer is right or not, but I'd really appreciate it if you could post the answer up after you know what it is so that I can see whether I got it right. At the very least hopefully this could give you some new insights to finish the problem correctly.