Question

Please explain how the presence or absence of tryptophan regulates the activity of the trp operon.

Answer 1

The Trp operon is made up of 4 geions namely 1, 2, 3 and 4 which regulate the binding of ribosome and also synthesis of protein by forming loops. The trp operon codes for the enzymes for trp biosynthezing pathway.

When trp levels are high in the cell, the ribosome translates the region 1 which has the ORF for the leader peptide and blocks the sequence 2 before the sequence 3 is transcribed. This leads to termination of the operon as the sequence 3 and 4 form a atteneutor loop.

When trp levels are low in the cell, the ribosome pauses at the sequence 1 which has the trp codons. The region 2 and 3 form a lop due to which the atteneution of the process is stopped. As the sequence 3 is not available for forming loop with sequence 4, the trp operon will be actively transcribed.