Bacterial Gene Regulation and the Lac Operon

Vocabulary flashcards covering the principles of prokaryotic gene regulation, mechanisms of activators and repressors, small effector molecules, and the structural components of the lac operon.

Constitutive Gene

A gene that is always transcribed and turned on at a set level to maintain general cellular functions, such as those encoding cytoskeletal components, ribosomes, and tRNAs.

Transcription Factor

A protein molecule that recognizes specific nucleotide sequences and binds directly to DNA, most commonly at or near the promoter region, to influence transcription.

Repressor

A transcription factor protein that binds to DNA sequences near the promoter region to hold back or inhibit RNA polymerase and decrease transcription.

Activator

A transcription factor protein that binds to DNA to enhance transcription by helping to recruit RNA polymerase.

Negative Control

Transcriptional regulation mediated by a repressor protein, wherein the presence and binding of the regulatory protein decreases transcription.

Positive Control

Transcriptional regulation mediated by an activator protein, wherein the presence and binding of the regulatory protein increases or initiates transcription.

Inducer

A small effector molecule that increases transcription by either binding an activator to enable its DNA binding or binding a repressor to prevent it from binding DNA.

Corepressor

A small effector molecule that binds to a repressor protein to help it bind to DNA and shut down transcription.

Inhibitor Molecule

A small effector molecule that binds to an allosteric site on an activator protein, altering its shape and preventing it from binding DNA, thereby repressing transcription.

Polycistronic mRNA

A single bacterial messenger RNA transcript that carries coding sequences for multiple distinct proteins, allowing coordinated expression.

Operator Site

A specific DNA sequence located adjacent to the promoter that provides a binding site for a regulatory protein, such as a repressor.

CAP Site

A specific DNA region near the promoter that binds the catabolite activator protein (CAP) to stimulate transcription of operons encoding alternative metabolic enzymes.

lacI Gene

A trans-acting gene with its own promoter that encodes the lac repressor, typically maintaining a low level of only a few dozen active tetrameric protein molecules per cell.

Allolactose

An altered form of lactose that acts as the physiological inducer for the lac operon by binding the lac repressor and causing an allosteric conformational change that removes it from the operator.

Diauxic Growth

A growth phenomenon in which an organism displays a sequential preference for food sources, consuming the most readily metabolized sugar (such as glucose) before switching on genes to consume alternative substrates.