TRP Operon

Question 1

Repression (trp)

Answer 1

1. When trp levels are high, trp will bind to the repressor protein causing a it to change shape.
2. Repressor can now bind to operator, inhibiting RNA polymerase from binding to promoter.
3. Structural genes of trp operon are not transcribed.

Question 2

Attenuation (trp)

Answer 2

1. When trp levels are high, RNA polymerase will begin transcription of the leader sequence which contains two trp codons within it.
2. If there are tRNA molecules carrying trp, then the ribosome translating the leader sequence (simultaneous with transcription) will not stall at the trp codons in region 1 of the leader.
3. Instead, the ribosome will stall at the STOP codon between region 1 and 2 of the leader. This causes a hairpin loop to form between regions 3 and 4, causing a termination loop.
4. RNA polymerase and the ribosome both detach as a result and there is no completion of transcription and translation of the structural genes.