Genetic Regulation in Bacteria

Flashcards about genetic regulation in bacteria.

What is the approximate ATP cost for a single copy of a 1,000 amino acid protein in E. coli?

Synthesizing a 1,000 amino acid protein in E. coli demands approximately 6,000 ATP molecules. This substantial energy investment highlights the significant cellular resources required for protein production, reflecting the complexity and precision of the process.

Why is expressing all genes at all times 'expensive' for a cell?

Constitutively expressing all genes is energetically 'expensive' because it necessitates continuous synthesis of mRNAs, tRNAs, ribosomes, and enzymes. This constant production consumes significant ATP, CTP, GTP, and UTP, draining cellular energy reserves and reducing efficiency.

What does it mean for a gene to be regulated?

Gene regulation involves controlling gene expression, switching genes 'on' or 'off' based on cellular needs or environmental signals. This dynamic control allows cells to conserve resources and respond effectively to changing conditions or developmental cues.

Are all genes regulated?

Not all genes are subject to regulation. Certain gene products, essential for core metabolic pathways or structural integrity, are constitutively expressed to ensure their constant availability, crucial for basic cellular functions.

Where can regulation occur in gene expression?

Gene expression regulation can occur at multiple steps: transcription initiation, transcript stability, translation initiation, translation rate, polypeptide stability, and protein activity. This multistep control provides diverse opportunities for fine-tuning gene expression.

At which level does regulation most frequently occur and why?

Regulation most often occurs at transcription initiation, offering an optimal balance between energy conservation and response speed. By controlling transcription, cells avoid unnecessary mRNA and protein synthesis while rapidly adapting to changing conditions.

What is an operon?

An operon is a genetic unit comprising multiple protein-coding regions (genes) controlled by a single promoter. Transcribed together as a polycistronic mRNA, it yields several individual proteins, streamlining coordinated gene expression.

What happens to E. coli in the presence of both glucose and lactose?

Given both glucose and lactose, E. coli preferentially utilizes glucose. Glucose induces catabolite repression to lower beta-galactosidase expression, ensuring the lac operon activates only when glucose is limited, optimizing energy use.

What is the function of beta-galactosidase?

Beta-galactosidase, encoded by the lac operon, metabolizes lactose by cleaving it into glucose and galactose, enabling E. coli to use lactose as an alternative energy source when glucose is scarce.

What is catabolite repression?

Catabolite repression describes glucose's ability to suppress genes required for metabolizing other sugars, like lactose. This ensures E. coli prioritizes glucose, its preferred energy source, when available, preventing wasteful enzyme production.

What is the role of LacI in the absence of lactose?

Without lactose, LacI (the lac repressor) tightly binds the operator, a specific DNA sequence near the lac operon promoter, preventing RNA polymerase from initiating transcription and thus blocking lac operon expression.

What happens when lactose is present in the cell?

In the presence of lactose, it converts to allolactose, which binds to LacI, reducing LacI's affinity for the operator. This releases the operator, allowing RNA polymerase to bind and transcribe the lac operon, initiating lactose metabolism.

How does glucose cause catabolite repression? Clarify cAMP and adenylate cyclase.

Glucose inhibits adenylate cyclase, reducing cAMP (cyclic AMP) levels. Since cAMP is needed for CAP (catabolite activator protein) to bind DNA and activate transcription, low cAMP diminishes lac operon transcription, prioritizing glucose use.

What is the role of cAMP and CAP in catabolite repression? How do they interact with the lac operon?

cAMP binds to CAP, and this complex binds a DNA sequence upstream of the lac operon promoter. This enhances RNA polymerase binding and increases transcription, but only when glucose is low, ensuring efficient lactose metabolism when glucose is scarce.

What are the key regulatory elements in the lac operon? List them and their roles.

Key lac operon regulatory elements include: LacI repressor (blocks transcription), operator (LacI binding site), promoter (RNA polymerase binding site), CAP (enhances transcription), and cAMP (activates CAP). They collectively control lac operon expression relative to glucose and lactose levels.

What is the effect of a mutation that prevents LacI from binding to lactose?

If LacI cannot bind lactose (or allolactose), it remains bound to the operator, preventing lac operon transcription regardless of lactose availability. This mutation constitutively represses the lac operon.

What is the effect of a mutation that prevents CAP from binding to cAMP?

If CAP cannot bind cAMP, it cannot effectively stimulate lac