Question

When the levels of trp inside a cell are high, transcription of the trp operon stops due to formation of a __________ caused by base pairing between regions ________ within the leader region.

A. stop codon, 2&3
B. trp codons, 3&4
C. stem-loop, 2&3
D. stem-loop, 3&4

Answer 1

D. stem-loop, 3&4

Step-by-step explanation:

When tryptophan levels are high, sequence 1 of leader peptide is quickly translated as it has two "trp" residues. Ribosome translates sequence 2 before sequence 3 is transcribed. This prevents the stem-loop formation between sequence 2 and 3.

The continued transcription and translation of the complementary sequences 3 and 4 followed by the formation of a stem-loop structure by these two sequences serve as an attenuator for transcription of trp operon.