26. [1pt] What effect would the following mutations have on the expression of th

Question

26. [1pt]
What effect would the following mutations have on the expression of the enzyme coding sequences of the tryptophan operon. Select the letter on the right that describes the effect. In all cases, the level of tryptophan is less than needed to bind the trp repressor. (If the first corresponds to B, and the next 3 to C, enter BCCC)

1) a mutation in region 3 that prevents it from base pairing with region 2? (It can still base pair with region 4.) A. decrease transcription when trp is low 2) a mutation in the leader peptide that changes a glycine codon into a tryptophan codon? B. never be transcribed 3) mutations in the leader peptide that change the trp codons to leucine codons? C. increase transcription when trp is low 4) a mutation in region 4 that prevents it from base pairing with region 3? D. be transcribed constitutively

Explanation / Answer

1) a mutation in region 3 that prevents it from base pairing with region 2? (It can still base pair with region 4.) ------------> B. never be transcribed (transcription of region 4 forms a stem loop with region 3, which prevents transcription).

2). A mutation in the leader peptide that changes a glycine codon into a tryptophan codon -----------> C. increase transcription when trp is low.

3). Mutations in the leader peptide that change the trp codons to leucine codons ---------------> A. decrease transcription when trp is low.

4) a mutation in region 4 that prevents it from base pairing with region 3 ---------------------> D. be transcribed constitutively

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