It doesn\'t tell me which of these is wrong, please help! How would transcriptio

Question

It doesn't tell me which of these is wrong, please help!

How would transcription of the E. coli trp operon be affected by the following manipulations of the leader region of the trp mRNA? Note: Only place "attenuated by Trp" or "not attenuated by Trp" in the "Effect on Attenuation" boxes Effect on Attenuation Explanation The ribosome is not bound to the sensor site, so attenuation cannot occur. (a) Increasing the distance (number not attenuated by Trp of bases) between the leader peptide gene and sequence 2 The translating ribosome is too far away to prevent 2:3 hairpin formation (b) Increasing the distance betweenattenuated by Trp (c) Removing sequence 4 (d) Changing the two trp codons sequences 2 and 3 Sequence 4 is required for attenuator formation. not attenuated by Trp in the leader peptide gene to his codons Histidine levels now regulate production of trp gene products not attenuated by Trp (e) Eliminating the ribosome-binding Only the 3:4 attenuator stem and loop can form not attenuated by Trp site for the gene that encodes the leader peptide (f) Changing several nucleotides in The 2:3 hairpin stem and loop is less likely to form, allowing the 3:4 attenuator to form sequence 3 so that it can base- pair with sequence 4 but not with sequence 2 attenuated by Trp attenuated by Trp not attenuated by Trp

Explanation / Answer

1.

Increasing distance between the leader peptide and sequence 2 - so 1 and 2 regions cannot form loop and hence trp increases. So no attenuation.

2.

Increasing distance between 2 and 3 , no anti terminator , so attenuation takes place.

3.

Removing sequence 4 - No termination , increase in trp . No attenuation.

4.

Changing 2 trp codons in leader - still trp function with His levels - No attenuation by trp.

5.

Eliminating ribosome binding site - No ribososme can bind - No transcription - Attenuation.

6.

Changing nucleotides in sequence 3 - No anti - Termination - Termination occurs - No trp - attenuation occurs.

(In general Attenuation - No trp ; No attenuation - trp production )

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