Prokaryotic Gene Regulation Quiz

Operon

• A group of genes that are transcribed together and code for functionally similar proteins
• Consists of promoter, operator, and genes for proteins

Key Players in Operon

• Promoter: a section of DNA where RNA polymerase binds
• Operator: controls activation of transcription, acting as an on/off switch between the promoter and genes for proteins
• Repressor protein: binds to the operator to block RNA polymerase and shut down transcription
• Corepressor: keeps the repressor protein on the operator
• Inducer: pulls the repressor off the operator, turning on the operon

Types of Gene Regulation

• Negative Regulation: a repressor protein binds to an operator to prevent a gene from being expressed
• Positive Regulation: a transcription factor is required to bind at the promoter to enable RNA polymerase to initiate transcription

Lac Operon Components

• Structural Genes:
• LacZ: encodes β-galactosidase, an enzyme that cleaves lactose into glucose and galactose
• LacY: codes for lactose permease, enabling lactose entry into the cell
• LacA: encodes transacetylase, which modifies lactose metabolites for excretion
• Operator (O): regulatory DNA sequence where a repressor protein binds, inhibiting transcription when lactose is absent
• Regulatory Genes:
• LacI: encodes the repressor protein, which suppresses transcription in the absence of lactose
• Inducer Molecule (Lactose): initiates operon transcription by binding to the repressor protein, rendering it inactive

The Central Principle of Gene Regulation

Cis-Acting Elements

• Definition: DNA sequences on the same chromosome as the regulated gene
• Function: Directly regulate adjacent genes, e.g., promoters, enhancers, silencers, operators
• Location: Non-coding regions: upstream (promoter), downstream (terminator), or within introns
• Effect: Modulate transcription rate, impacting overall gene expression levels

Trans-Acting Factors

• Definition: Proteins or molecules regulating genes, produced by different genes, binding to cis-acting elements
• Function: Bind to cis-acting elements, directly influencing target gene transcription
• Location: Synthesized in the same or different cells within an organism
• Effect: Presence, absence, and affinity for cis-acting elements dictate gene expression levels

Regulation of Transcription in Eukaryotes

• Eukaryotic DNA: packaged into chromatin, which limits its availability as a template for transcription
• Non-coding RNAs and Proteins: regulate transcription via modifications of chromatin structure
• Cis-Acting Sequences: many regulate expression of eukaryotic genes
• Identification of Eukaryotic Regulatory Sequences: using Gene Transfer Assays and Transfection

Promoter

• Definition: The region of DNA involved in the initiation of transcription
• Function: Provides a binding site for RNA polymerase and other proteins necessary for transcription

Enhancers

• Definition: Regulatory sequences located farther away from the start site
• Function: Bind transcription factors that then regulate RNA polymerase
• Location: Can be located at a distance from the promoter, and can even be found on a different chromosome

Repressors

• Definition: Proteins that inhibit gene expression by binding to specific DNA sequences
• Function: Turn off transcription by blocking activators from binding to enhancers

Insulators

• Definition: Specific DNA sequences that define chromatin domain boundaries
• Function: Regulate interactions between enhancers, silencers, and promoters
• Role: Maintain enhancer-promoter specificity, and organize chromosomes into looped domains

Transcriptional Activators

• Definition: Proteins that stimulate transcription by binding to regulatory DNA sequences
• Have two independent domains: one region binds DNA, the other stimulates transcription

Test your knowledge on the transcriptional regulation and epigenetics in prokaryotes, focusing on the operon concept. Learn about key players like promoter, operator, repressor protein, and corepressor.