Ch. 16 Flashcards: Control of Gene Expression in Prokaryotes

Vocabulary practice flashcards covering the control of gene expression in prokaryotes, including operon structure, the lac and trp operons, catabolite repression, attenuation, and RNA regulatory mechanisms.

Structural Genes

DNA sequences that encode proteins used in metabolism, biosynthesis, or cell structure.

Regulatory Genes

Genes encoding products (such as transcription factors) that interact with other sequences and affect the transcription or translation of those sequences.

Regulatory Elements

DNA sequences that are not transcribed into RNA but play a role in regulating other nucleotide sequences or genes, such as consensus sequences.

Constitutive Expression

The continuous expression and transcription of a gene under normal cellular conditions.

Positive Control

A regulatory mechanism that stimulates gene expression (turns transcription on) via an activator protein.

Negative Control

A regulatory mechanism that inhibits gene expression (turns transcription off) via a repressor protein.

DNA-Binding Domain

A discrete region of approximately $60\text{ to }90$ amino acids in a protein responsible for binding DNA by forming dynamic hydrogen bonds with DNA bases.

Motif

A simple structural fold within a protein's binding domain that fits into the major groove of DNA to recognize and bind specific nucleotide sequences.

Helix-Turn-Helix

A DNA-binding motif consisting of two alpha helices that bind the major groove of DNA, common in bacterial regulatory proteins.

Zinc-Finger

A DNA-binding motif consisting of a loop of amino acids with a zinc ion at the base that binds into the major groove of DNA, common in eukaryotic regulatory proteins.

Leucine-Zipper

A DNA-binding motif found in eukaryotic transcription factors characterized by a helix of leucine residues where two leucine residues interdigitate, with a basic arm binding two adjacent major grooves.

Operon

A group of bacterial structural genes that are transcribed together, along with their promoter and operator sequences that control transcription.

Operator

A regulatory DNA sequence in an operon to which a regulator protein binds to govern the transcription of the operon's structural genes.

Inducible Operon

An operon whose transcription is normally turned off and requires a specific molecule to turn it on.

Repressible Operon

An operon whose transcription is normally turned on and requires a specific regulatory molecule to turn it off.

Inducer

A small molecule that binds to a regulator protein to trigger transcription in an inducible operon.

Corepressor

A small molecule that binds to an inactive repressor protein, enabling it to bind the operator and shut off transcription in a repressible operon.

Allosteric Protein

A protein that changes its conformation upon binding with another molecule, altering its functional activity.

Coordinate Induction

The simultaneous synthesis of several structural proteins stimulated by a single specific molecule (an inducer), demonstrated by François Jacob and Jacques Monod in 1961.

lacZ

A structural gene in the lac operon that encodes the enzyme $\beta\text{-galactosidase}$.

lacY

A structural gene in the lac operon that encodes the membrane transport protein permease.

lacA

A structural gene in the lac operon that encodes the enzyme transacetylase.

Allolactose

A converted isomer of lactose produced by $\beta\text{-galactosidase}$ that acts as the physiological inducer for the lac operon.

Partial Diploid

A bacterial cell carrying a complete native chromosome plus an extra piece of DNA delivered on an F plasmid (merozygote).

Trans-Acting

The capacity of a diffusible gene product to control the expression of genes located on other DNA molecules within the cell.

Cis-Acting

The property of a DNA sequence to control the expression of adjacent genes only when located on the exact same piece of DNA.

lacI^s

A superrepressor mutation in the regulator gene producing a repressor that cannot bind lactose/allolactose, causing trans-dominant permanent repression of transcription.

lacO^c

A constitutive operator mutation that alters the operator sequence so the repressor cannot bind, causing continuous cis-dominant transcription of structural genes on that DNA molecule.

Catabolite Repression

A regulatory mechanism where bacteria preferentially use glucose over other sugars by repressing the metabolism of secondary sugars such as lactose.

Catabolite Activator Protein (CAP)

A positive regulator protein that, when complexed with cAMP, binds upstream of the lac promoter and bends DNA to facilitate RNA polymerase binding.

Cyclic AMP (cAMP)

Adenosine-$3', 5'$-cyclic monophosphate; a signaling nucleotide whose concentration is inversely proportional to glucose levels and binds CAP to stimulate transcription.

trp Operon

A negative repressible operon in E. coli consisting of five structural genes (trpE, trpD, trpC, trpB, trpA) encoding enzymes that convert chorismate to tryptophan.

Attenuation

A regulatory mechanism in bacterial operons causing premature termination of transcription in the 5' UTR before RNA polymerase reaches the structural genes.

Attenuator

A $3+4$ hairpin secondary structure followed by a poly-U tract in the trp operon 5' UTR that mimics an intrinsic terminator to abort transcription when tryptophan is high.

Antiterminator

A $2+3$ hairpin secondary structure in the trp operon 5' UTR that prevents the formation of the $3+4$ attenuator, allowing transcription to proceed when tryptophan is low.

Antisense RNA

A small RNA molecule complementary to a targeted partial sequence of mRNA that binds to inhibit translation or regulate expression.

Riboswitch

A regulatory sequence in mRNA where the binding of a regulatory molecule or protein stabilizes an alternative secondary structure to mask or reveal a ribosome-binding site.

Ribozyme

An RNA molecule with catalytic activity that can affect gene regulation.