Regulation of Gene Expression

Vocabulary flashcards covering bacterial gene regulation, operons (lac, gal, trp, ara, fab), post-transcriptional control, riboswitches, quorum sensing, two-component systems, and chemotaxis.

Constitutive genes

Genes that are constantly turned on and needed by the cell at all times.

Inducible genes

Genes that are required and expressed only at particular times.

Operon

A transcriptional unit containing a series of structural genes and their associated transcriptional regulatory elements.

Polycistronic mRNA

An mRNA molecule containing multiple open reading frames, allowing several distinct polypeptides to be synthesized sequentially by the same ribosome.

Promoter

A site on DNA bound by RNA polymerase that directs the initiation of transcription.

Activator

A protein that binds to a site on DNA to assist the binding of RNA polymerase to the promoter, resulting in increased transcription initiation.

Activator binding site

A specific sequence or site on DNA bound by an activator protein.

Repressor

A protein that binds to the operator on DNA, inhibiting transcription.

Operator

A site on DNA bound by a repressor protein to inhibit transcription.

Effector

A small molecule that binds to activator or repressor proteins, modifying their gene regulation activity.

Inducer

An effector molecule that increases transcription by enabling an activator or disabling a repressor.

Corepressor

An effector molecule that decreases transcription by enabling a repressor protein.

lacZ

A gene in the lac operon that encodes β-galactosidase, an enzyme that cleaves lactose into glucose and galactose subunits.

lacY

A gene in the lac operon that encodes a permease responsible for transporting lactose into the cell.

LacI repressor

A transcriptional regulator encoded by the lacI gene that binds to the lac operator to block transcription of the lac operon.

Allolactose

A disaccharide formed occasionally from lactose inside the cell that functions as an inducer by binding and inactivating the LacI repressor.

Cyclic AMP (cAMP)

A signaling molecule that accumulates when glucose is depleted, acting as a coactivator by forming a complex with CRP to increase RNA polymerase affinity for the lac promoter.

Diauxic growth

A biphasic pattern of bacterial growth resulting from coordinated regulation when Escherichia coli is grown in the presence of two carbon sources, such as glucose and lactose.

X-gal

A chemical analog of lactose that produces a blue-colored product upon cleavage by β-galactosidase, used to assess enzyme activity.

Negative inducible system

A regulatory mechanism, such as the lac or gal operons, in which the binding of an effector molecule to a repressor protein relieves transcription inhibition.

Negative repressible system

A regulatory mechanism, such as the trp operon, in which binding of a corepressor effector converts an inactive aporepressor into an active repressor that inhibits transcription.

Aporepressor

An inactive repressor protein, such as TrpR, that requires binding to a specific corepressor molecule to become active and bind DNA.

AraC

A regulatory protein of the ara operon that acts as an activator when bound to arabinose and as a repressor/antiactivator when unbound.

Positive repressible system

A regulatory mechanism, such as the fab operon, where an effector molecule inactivates an activator protein (e.g., FadR) to turn off transcription.

Transcription attenuation

A post-transcriptional regulatory mechanism where translation rates affect mRNA secondary structure formation, leading to premature termination of transcription.

TRAP

An RNA-binding protein in Bacillus subtilis that facilitates the formation of a terminator structure in the trp operon mRNA in the presence of tryptophan.

sRNA (small RNA)

Antisense regulatory RNA molecules, such as DsrA, that base-pair with target mRNA to alter secondary structure, influencing mRNA stability and translation access.

Riboswitch

A cis-regulatory element within an mRNA molecule that directly binds a small effector molecule, altering mRNA conformation to control transcription or translation.

Quorum sensing

A cell-density-dependent communication system in bacteria that utilizes signaling molecules to coordinate collective physiological processes.

Autoinducer

A chemical signal molecule, such as N-acyl-homoserine lactone (AHL), produced and secreted by bacteria to measure population density during quorum sensing.

Sensor Kinase

The membrane-bound protein (Component 1) of a two-component regulatory system that senses external signals and autophosphorylates using ATP.

Response Regulator

The cytoplasmic protein (Component 2) of a two-component system that receives a phosphate group from a sensor kinase to alter target gene transcription or cellular behavior.

Methyl-accepting Chemotaxis Protein (MCP)

A transmembrane receptor protein that senses attractants or repellents and directs flagellar rotation via signal transduction pathways.

CheY

A response regulator in bacterial chemotaxis that, when phosphorylated to CheY-P, binds the flagellar motor to induce clockwise rotation and cell tumbling.