Chapter 7 Operons: Fine Control of Bacterial Transcription

This set of vocabulary flashcards covers the fundamental concepts, structures, and regulatory mechanisms of the lac and trp operons in E. coli based on the lecture transcript.

Polycistronic message

A single mRNA that contains the sequences for multiple genes, such as the three genes of the lac operon, which are transcribed together from a single promoter.

Galactoside permease (lacY)

A protein encoded by the lac operon that transports lactose into the E. coli cells.

β-galactosidase (lacZ)

An enzyme that cuts lactose into galactose and glucose.

Galactoside transacetylase (lacA)

The third gene in the lac operon; its specific function remains unclear.

Ribosome binding site (RBS)

A specific sequence located on each cistron of a polycistronic mRNA where ribosomes bind independently to begin translation.

Lac repressor

A protein that binds to the operator to prevent RNA polymerase from binding to the promoter, thereby repressing the operon when no lactose is available.

Allosteric protein

A protein, such as the Lac repressor, whose shape at a remote site is changed by the binding of an effector molecule, altering its interaction with a second molecule.

Inducer

A molecule that binds to the repressor, causing a conformational change that favors the repressor's release from the operator.

Major lac operator (O1)

The primary operator site located adjacent to the promoter; it produces a modest amount of repression on its own.

Catabolite repression

A process where a glucose breakdown product (a catabolite) is used to repress the operon, favoring the use of glucose over other sugars.

DNA footprinting (DNase I footprinting)

An in vitro technique used to identify the specific binding site of a protein, such as a transcription factor, on a DNA molecule.

Cyclic-AMP (cAMP)

A nucleotide whose concentration rises as the concentration of glucose drops, acting as a signal for the lack of glucose.

Catabolite activator protein (CAP)

A positive controller that, when bound to cAMP, helps RNA polymerase form an open promoter complex to activate the lac gene.

Anabolic enzymes

Enzymes that build up a substance and are typically turned off by a high level of the substance they produce, such as the enzymes in the trp operon.

Aporepressor

An inactive protein that becomes a functional repressor only after binding to a specific corepressor, such as tryptophan.

Corepressor

A substance, like tryptophan, that binds to an aporepressor to form a functional repressor complex that can bind to the operator.

Attenuation

A mechanism of control that causes premature termination of transcription when the product of the operon is abundant, providing an extra level of regulation.

Trp-leader

A sequence between the operator and the first gene of the trp operon that contains a translation start site and two tryptophan codons in a row.

Trp-attenuator

A sequence within the trp operon that contains transcription termination signals, such as inverted repeats that form hairpin structures followed by a string of U's.