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Trp Operon: Gene Regulation in Prokaryotes [With Attenuation]

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.

 

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Lac Operon: Negatively Controlled Inducible Operon [Gene Regulation in Prokaryotes]

Lac Operon – Negatively Controlled Inducible Operon

Lac operon is an operon required for the transport and metabolism of lactose in E. coli and some other enteric bacteria. Francois Jacob and Jacques Monod studied gene expression and formulated an operon model.

It consist of 3 adjacent structural genes, a promoter, an operator, a regulator and a terminator. It is regulated by several factors including the availability of glucose and lactose. (An operon is cluster of genes together under a single operon)

It is a negatively controlled inducible operon of gene regulation in prokaryotes because here binding of repressor inhibits transcription.

In simple terms, lac operon is off when lactose is absent and is switched on when lactose is present in the environment.

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.

This operon has three structure genes: lacA, lacY and lacZ

Promoter (lacP) : is the site where RNA polymerase binds to DNA to begin transcription.

Operator (lac O): resides adjacent to promoter and it serve as binding site for repressor (a gene regulatory protein which is like an off switch)

Inhibitory gene: lac i which codes for repressor protein.

00:23 introduction of operon system in prokaryotes

06:26 Lac operon in detail

12:02 Mechanism

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.