The mmm operon, which has sequences A, B, C, and D, encodes enzymes 1 and 2. Mut
ID: 62528 • Letter: T
Question
The mmm operon, which has sequences A, B, C, and D, encodes enzymes 1 and 2. Mutations in sequences A, B, C, and D have the following effects, where a plus sign (+) means that the enzymes are synthesized, a minus sign () means that the enzymes are not synthesized, and a pound (#) means that the enzymes are synthesized but are not functional.
mmm absent mmm present
Enzyme 1 Enzyme 2 Enzyme 1 Enzyme 2
Wild-type + +
Mutation in A # +
Mutation in B + + + +
Mutation in C + #
Mutation in D
(a) Is the mmm operon inducible or repressible? Explain your answer.
(b) Indicate which sequence (A, B, C, or D) is part of the following components of the operon and explain your answer.
Regulator gene:
Promoter:
Structural gene for enzyme 1:
Structural gene for enzyme 2:
Explanation / Answer
a) mmm operon seems to be repressor, see in wild-type in the absence operon, it is able to synthesize E1 and E2. But, when operon is present, the E1 and E2 found to be absent in wild-type that indicates the mmm operon is repressor at normal conditions.
b) Regulator is B: Since, in the presence or absence of operon or mutation it is producing E1 and E1 that indicates it would be positive regulator.
Promoter is D: Promoter does not code for any enzyme either in presence or absence of mutation or operon.
Structural gene for E1 : A, since, if A is mutated that leads to synthesize normal E2 but non-functional E1.
Structural gene for E2: C, since, if C is mutated that leads to synthesize normal E1 but non-functional E2.
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