Gene Regulation: Operons, Repressors, and Attenuation in Bacteria

What are regulatory structural genes?

Genes that code for regulatory proteins.

What are constitutive genes?

Genes that are always expressed and code for essential proteins.

What do regulatory genes code for?

Transcription factor proteins that control gene expression.

What is the function of transcription factors?

They bind to DNA at the operator region to control gene action.

What is an operon?

A group of closely related genes that act together to regulate a metabolic activity.

What components make up an operon?

Structural genes, an upstream promoter region, and an operator region.

What is a repressible system in gene regulation?

A system that is normally active but can be inactivated by a co-repressor.

What is the trp operon?

A repressible system that includes genes coding for enzymes in tryptophan synthesis.

How does tryptophan affect the trp operon?

High levels of tryptophan activate the repressor protein, blocking transcription.

What happens when tryptophan levels are low in the cell?

The trp-repressor protein is inactive, allowing RNA polymerase to transcribe the operon.

What is attenuation in the context of the trp operon?

A mechanism that reduces expression by preventing completion of transcription.

What occurs during attenuation when tryptophan levels are high?

RNA polymerase stops prematurely, resulting in an incomplete mRNA.

What happens during attenuation when tryptophan levels are low?

The ribosome stalls, allowing the formation of an antiterminator hairpin, which permits transcription.

What is the role of the ribosome in attenuation?

It influences the formation of hairpins that determine whether transcription continues or stops.

What is the outcome when tryptophan levels are high during transcription?

The terminator hairpin forms, causing RNA polymerase to detach and stopping transcription.

What is the difference between the antiterminator and terminator hairpins?

Antiterminator allows transcription to continue; terminator causes RNA polymerase to detach.

What is the significance of the operator region in gene regulation?

It is where repressor proteins bind to control gene expression.

What are structural genes?

Genes that code for proteins or RNAs not involved in regulation.

How does the trp operon respond to low tryptophan levels?

Transcription of the structural genes occurs, producing enzymes for tryptophan synthesis.

What is the function of the co-repressor in the trp operon?

It binds to the repressor protein, enabling it to bind to the operator and block transcription.

What is the primary function of the trp operon?

To regulate the synthesis of the amino acid tryptophan.