Trp Operon with Attenuation – Easy to Understand
Trp operon codes for 5 enzymes which are required for the biosynthesis of amino acid tryptophan. Trp operon is a negatively controlled repressible operon. In a system if there is low or no tryptophan available, it is in ON condition and when tryptophan is available in high concentration it is in OFF condition.
It contains 5 structural genes: trp E, trp D, trp C, trp B and trp A. Trp repressor binds and block the transcription of these genes when tryptophan is present.
Structural genes: codes for enzymes. Structural gene of an operon usually lie adjacent to one another and RNA polymerase moves from one structural gene to the next, transcribing all of the genes into a single mRNA which is translated into enzymes.
Attenuation is a fail safe mechanism to regulate the tryptophan operon in the presence of tryptophan. Attenuation prevents the completion of transcription rather than blocking it.
00:22 introduction
00:54 introduction on Tryptophan operon
04:26 mechanism of Tryptophan operon
08:11 attenuation mechanism (really easy to understand)
14:38 intrinsic termination loop and anti-terminator loop
Have you watch the video on lac operon? If not watch it here to understand this topic better; Lac Operon – Negatively Controlled Inducible Operon.
Do you want to know what happens if glucose and lactose both are present in the environment? Check out Catabolite Repression – Positive Control of Lac Operon here.