Summary
A repressible operon turned off when tryptophan accumulates and activates the repressor.
In depth
Tryptophan acts as a corepressor: when it is plentiful it binds the repressor and enables it to block transcription. Attenuation adds further control by terminating transcription early if charged tRNA-Trp is abundant.
Anabolic pathways are typically repressible, catabolic ones inducible.
When tryptophan is abundant, cells stop making it. Two layers act: the repressor (activated by tryptophan) blocks initiation, and attenuation controls termination within the leader region. In attenuation, the ribosome translates a short leader peptide containing tryptophan codons; if tryptophan is scarce the ribosome stalls, an anti-terminator hairpin forms and transcription continues. If plentiful, a terminator forms.
Attenuation exploits the fact that bacterial transcription and translation are coupled, which cannot occur in eukaryotes. The pathway also uses feedback inhibition of the first enzyme, so there are three levels of control.
Remember: lac is inducible and catabolic, trp is repressible and anabolic.
Frequently asked questions
What is Trp Operon?
A repressible operon turned off when tryptophan accumulates and activates the repressor.
Which area of biology covers Trp Operon, and how advanced is it?
Trp Operon is one of the 52 topics in Molecular Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Transcription, Riboswitches, Lac Operon.
Can you give an example of Trp Operon?
E. coli stops making tryptophan when it grows in a rich medium.
What should I learn before Trp Operon?
Work through the Beginner topics in Molecular Biology first, such as Central Dogma, DNA Replication, Base Pairing, then return to Trp Operon. Intermediate topics assume the Beginner vocabulary.
What topics are related to Trp Operon?
The closest topics to Trp Operon are Transcription, Riboswitches, Lac Operon, Operon. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Trp Operon?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Trp Operon. To practise the whole of Molecular Biology, use the Molecular Biology quiz.
How is Trp Operon different from Transcription?
Trp Operon: A repressible operon turned off when tryptophan accumulates and activates the repressor. Transcription: The process of making an RNA copy of a gene using DNA as a template. Read both side by side and note what each one explains.
How should I study Trp Operon step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Transcription and explain the difference aloud. Finally, take the Molecular Biology quiz and come back to this page for any question you miss.