Answer the following question given this paragraph: 

Structure of the trp operon. The trp operon is composed of 5 structural genes, 1 regulatory gene and other regulatory sequences, including the promoter, operator and leader sequence. Within the leader sequence is the attenuator region. In the presence of tryptophan, the structural genes are not transcribed.


Q: What happens to structural genes in the presence of tryptophan?

 Choices:

- they are not oxidised

- they are transcribed

- they are exterminated​

- they are not transcribed

A:
they are not transcribed
