TRP operon - tryptophan regulation

What is a biochemical pathway?

Series of enzyme-mediated reactions where the product of one reaction is the substrate of the next; also called a metabolic pathway.

Why are biochemical pathways regulated?

To conserve energy when the products are not needed.

What is gene regulation?

A mechanism that acts like an on/off switch to prevent transcription and translation of proteins that are not needed, saving cellular energy (ATP).

What is an operon?

A cluster of genes in prokaryotes that code for proteins with related functions and are transcribed together under the control of a single promoter and operator.

Where are operons found?

In bacteria; only in prokaryotes.

In operons, when do transcription and translation occur?

Simultaneously.

What is the trp operon?

"An operon in E. coli where genes code for enzymes that make tryptophan; normally ""on"" but can be repressed by a repressor protein or regulated by attenuation."

What is tryptophan (trp)?

An amino acid.

What happens when trp levels are high (repressor regulation)?

Tryptophan binds to the repressor, activating it. The active repressor binds to the operator, blocking RNA polymerase from binding to the promoter, stopping transcription and gene expression.

What happens when trp levels are low (repressor regulation)?

The repressor remains inactive, cannot bind to the operator, and RNA polymerase can initiate transcription and translation of genes.

What is attenuation in gene regulation?

A mechanism that stops completion of transcription when tryptophan levels are high.

What is the leader sequence?

A segment of mRNA that codes for a short polypeptide and includes trp codons.

What is the attenuator?

A segment of mRNA with self-complementary regions that can form hairpin structures to regulate transcription.

What happens during attenuation when trp is high?

Fast translation allows terminator hairpin to form, causing RNA polymerase to detach and stopping transcription.

What happens during attenuation when trp is low?

Slow translation allows anti-terminator hairpin to form, letting transcription continue and the operon to be expressed.

What is the summary of repression when trp is high?

Two trp molecules bind to the repressor, changing its shape so it can bind the operator and block RNA polymerase from transcribing the genes.

What is the summary of attenuation when trp is high?

RNA polymerase begins transcription of the leader or attenuator sequence. Within this sequence, there are two trp codons. As the ribosome does not stall here, a hairpin termination loop forms, resulting in the detachment of both RNA polymerase and the ribosome. As the full mRNA is not transcribed, the required enzymes are not translated at the ribosome and tryptophan will not be synthesised

What is the purpose of repression and attenuation?

To regulate trp levels and conserve energy in prokaryotes.

What is an inducible operon?

An operon that is normally off and only turns on when needed.

What is a repressible operon?

An operon that is normally on and can be turned off when not needed.

Fill in the blanks: Like regulation by the _ repressor, _ is a mechanism for _ expression of the trp operon when levels of tryptophan are _.

trp, attenuation, regulating, high.

What is the difference between repression and attenuation?

Repression blocks initiation of transcription; attenuation prevents completion of transcription.

What is the mechanism for attenuation?

Terminator hairpin loop formation.

What kind of mRNA is produced when attenuation halts transcription?

A short mRNA that does not encode tryptophan biosynthesis enzymes.

What does attenuation depend on?

Coupling of transcription and translation—specifically, translation of a leader mRNA that is still being transcribed.