Bacterial Gene Regulation: Operons and Attenuation

Vocabulary practice flashcards covering operon structure, the lac and trp operons, repressor functions, and the bacterial attenuation mechanism.

Operon

A regulatory genetic unit started by a single promoter, flanked by regions that interact with transcription factors, and containing the coding sequences to produce messenger RNA for needed proteins.

Operator Sites

Specific nucleotide sequences located around the promoter of an operon that interact with transcription factors and repressor proteins.

Lac Repressor

A regulatory protein that binds to operator sites in the lac operon, creating a loop or kink in the DNA that physically blocks RNA polymerase from transcribing.

$O_1$ Operator Site

The central operator site located immediately downstream of the promoter in the lac operon that serves as a direct roadblock to RNA polymerase.

Tryptophan

An amino acid coded for by only one codon without redundancy whose synthesis requires a costly five-gene metabolic pathway in bacteria.

trpR

The trans element that codes for the repressor protein in the trp operon system.

Corepressor

An effector molecule, such as tryptophan, that binds to an inactive repressor protein to enable it to bind the operator and repress transcription.

trpL

The leader region located between the operator and structural genes of the trp operon that encodes a short peptide and contains the attenuator sequence.

Attenuation

A secondary regulatory mechanism in bacteria where transcription is prematurely terminated before structural genes are transcribed, depending on the coordination of transcription and translation.

Coupled Transcription and Translation

The simultaneous occurrence of transcription and translation on the same messenger RNA molecule, possible exclusively in bacteria because they lack a nucleus.

Stem-loops

Temporary double-stranded secondary conformations formed within single-stranded messenger RNA through complementary base pairing (primarily C-G matches) that regulate transcription continuation or termination.