Chapter 6: 6.8 Prokaryotic Operons: Tryptophan (Trp) Operon Flashcards
What is Tryptophan? What is a Tryptophan Operon?
- Tryptophan: An amino acid
- Tryptophan Operon: Present in some bacteria to produce tryptophan when it is low in the cell
True or False:
Tryptophan metabolism is under the control of two promoters
False, it is under the control of a single promoter
Genes encoded in the Trp Operon are involved in…
Trp Biosynthesis
Define:
TrpR
A repressor protein
* Binds to the Operator (O)
Define:
Trp
(What is it to the operon?)
A co-repressor
What proteins are required for production of tryptophan?
Structure genes (TrpA - E)
What would happen on the Trp Operon if:
* There were high Trp concentrations?
Binds to the allosteric site of the Trp repressor
* Activates the repressor site
* Blocks transcription of the operon
* No tryptophan produced
What would happen on the Trp Operon if:
* There were low Trp concentrations?
Inactivates the Trp repressor
* Allows transcription of operon
* Produces tryptophan
What is the Trp Operon expression dependent on?
- Concentration of Trp in the cytosol
- Number of charged tRNA
What does charged tRNA mean?
(In terms of a Trp Operon)
tRNA actually carrying a Trp amino acid
What is attenuation on a Trp Operon regulated by?
TrpL sequence (called a leader transcript)
True or False:
If there are a lot of Trp-tRNA’s, the ribosome can translate it quickly
True
If there is a high number of charged tRNA (high Trp concentration):
How does the loop structure form?
- 2-3 loop cannot form as the ribosome is physically on top of the sequence 2
- 3-4 loop forms, which is a transcription termination sequence
If there is a low number of charged tRNA (low Trp concentration):
How does the loop structure form?
- Slower translation
- Allows sequence 2-3 to form a hairpin loop
- Prevents sequence 3-4 from forming a hairpin loop (termination sequence)
- Allows transcription of the trp operon to continue
