There is a soultion in the chapter answer section, but if you could explain it b

Question

There is a soultion in the chapter answer section, but if you could explain it better in some way, I would greatly appriciate it.

Attenuation of trp operon transcription is controlled by the formation of stem-loop structures in mRNA by mutations that alter the sequence of repeat DNA regions 1 to 4 and prevent the formation of mRNA stem l Part A The attenuation function can be disrupted Determine the likely effects on attenuation of each of the following mutations under the conditions specified Drag the appropriate items to their respective bins Mutated Region a. Region 1 b. Region 1 c. Region 2 d. Region 2 e. Region 3 f. Region 3 g. Region 4 h. Region 4 Tryptophan Level Low High Low High Low High Low High transcription does not occur transcription occurs

Explanation / Answer

The tryptophan operon is a repressible operon which means that the presence of substrate or tryptophan prevenets expression of the genes in the cistron of the operon. Importantly, this operon undergoes structural control over gene expression by formation of a specialized semi-self-complementary hair-pin structure. There are total 4 regions for self-complementarity, hence three types of hair-pins can be formed. This suggests that mutation in any of these hair-pin regions will prevent formation of the hair-pin, hence allow the RNA polymerase to freely move across the gene, hence overexpression. Secondarily, presence of tryptophan in the medium will repress the operon as well.

Thus, based upon this background information, the answers can be found as below:

a. Transcription occurs (Low levels of tryptophan promote gene expression)

b. No transcription (high tryptophan levels prevent gene expression)

c. Transcription occurs (low levels of tryptophan promote gene expression)

d. No transcription (high tryptophan levels prevent gene expression)

e. Transcription occurs (mutation of region 3 prevents formation of loop, low levels of tryptophan promote gene expression)

f. No transcription (No pause-loops formed, but high tryptophan levels repress the operon)

g. Transcription occurs (Termination loop failed to be formed)

h. No transcription (Operon repressed)

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