Biological Sciences - Gene Regulation

What is gene regulation?

Gene regulation is the process by which cells control the expression of genes, determining when and how much of a gene product is made. This mechanism is crucial for cellular function, development, and response to environmental changes.

What levels can cells regulate?

Cells can regulate gene expression at multiple levels, including transcriptional, post-transcriptional, translational, and post-translational levels.

What is the most prominent level of gene regulation in prokaryotes and eukaryotes?

The most prominent level of gene regulation in both prokaryotes and eukaryotes is transcriptional regulation, where the transcription of DNA to mRNA is controlled.

What is an activator in transcription?

An activator in transcription is a protein that increases the likelihood of transcription of a particular gene by binding to nearby DNA. It enhances the recruitment of RNA polymerase to the promoter region, facilitating gene expression.

What is a repressor in transcription?

A protein that inhibits gene expression by binding to specific DNA sequences, blocking transcription.

How do activators work in gene expression?

Activators work by binding to specific DNA sequences near a gene's promoter, enhancing the recruitment of RNA polymerase and facilitating the transcription process, thereby increasing gene expression.

How do repressors work in gene expression?

Repressors work by binding to specific DNA sequences near a gene's promoter, preventing the recruitment of RNA polymerase and inhibiting the transcription process, thereby decreasing gene expression.

Cells control the level of transcription, what does this mean?

It means that cells can regulate how much mRNA is produced from a gene, influencing the amount of protein synthesized. This regulation is essential for cellular function and adaptation to environmental changes. This control allows cells to respond dynamically to internal and external signals, ensuring appropriate gene expression levels for different conditions. The cell can make a small amount of the mRNA or a medium amount or mRNA, or a large amount of the mRNA.

What is an operon?

An operon is a cluster of genes under the control of a single promoter, allowing for coordinated regulation of gene expression in prokaryotes. This system enables the bacteria to efficiently respond to environmental changes by turning on or off multiple related genes simultaneously.

What is an operator?

An operator is a specific DNA sequence within an operon that serves as a binding site for repressor proteins, regulating the transcription of the associated genes.

What is a set of genes?

that are regulated together, often functioning in a related pathway or process.

What is polycistronic mRNA?

Polycistronic mRNA is a type of messenger RNA that encodes multiple proteins from a single transcript, commonly found in prokaryotes. This allows for the coordinated expression of genes within an operon.

An operon consist of what?

A promoter, operator, set of genes, and a terminator.

What does trp stand for?

Tryptophan, an amino acid involved in protein synthesis and regulation.

If tryptophan is absent then the operon will be…

ON, allowing for the transcription of genes needed for tryptophan synthesis. Tryptophan will be transcribed.

-tryptophan=ON

If tryptophan is present then the operon will be…

OFF, preventing the transcription of genes involved in tryptophan synthesis. Which mean sit is not transcribed.

+tryptophan=OFF

What is the tryptophan repressor?

A protein that binds to the operator of the trp operon in the presence of tryptophan, inhibiting transcription.

How is the tryptophan repressor controlled?

The tryptophan repressor is controlled by the levels of tryptophan; when tryptophan is abundant, it binds to the repressor, activating it to inhibit transcription of the trp operon.

In the presence of tryptophan is the trp repressor bound or unbound?

The tryptophan repressor is bound, inhibiting transcription of the trp operon.

In the absence of tryptophan is the trp repressor bound or unbound?

In the absence of tryptophan, the repressor is unbound, allowing transcription of the trp operon to proceed.

when the trp repressor is not bound to the operator, DNA polymerase will bind to the promoter and transcribe the operon (the operon will be expressed).

This allows for the synthesis of tryptophan when it is scarce. This mechanism ensures that the cell can produce tryptophan only when necessary, conserving resources.

When trp repressor is bound to the operator, RNA polymerase cannot bind to the promoter and will not be able to transcribe the operon (the operon will not be expressed).

This prevents the synthesis of tryptophan when it is abundant.

The lac operon allows a bacterial cell to do what?

Regulate the metabolism of lactose by controlling the expression of genes involved in its uptake and breakdown. Utilizes lactose as an energy source.

What controls the lac operon?

The presence of lactose and glucose levels, along with the lac repressor and CAP protein, regulate the operon's expression.

Where does the lac activator bind?

The lac activator binds to the promoter region (CAP site) of the lac operon, facilitating RNA polymerase binding and promoting transcription.

Where does the lac repressor bind?

The lac repressor binds to the operator region of the lac operon, inhibiting transcription by blocking RNA polymerase access.

Can the activator express a gene if the repressor is bound to the operator?

No, the activator cannot express the gene if the repressor is bound to the operator, as the repressor blocks RNA polymerase access, preventing transcription.

What controls the levels of activity in the lac operon?

The levels of activity in the lac operon are controlled by the presence or absence of lactose and glucose, which influence the binding of the lac repressor and the lac activator.

The levels of lactose control what?

the binding of the lac repressor, affecting transcription levels in the lac operon.

The levels of glucose control what?

the activity of the lac activator, influencing transcription of the lac operon.

When will bacterial cells want to use lactose?

Bacterial cells will want to use lactose when glucose levels are low, allowing the activation of the lac operon for lactose metabolism.

When will bacterial cells want to use glucose?

Bacterial cells will want to use glucose when lactose levels are low, as glucose is the preferred energy source for metabolism.

Which do bacteria prefer?

Bacteria prefer glucose over lactose, as it is a more efficient energy source.

If glucose is present and lactose is present

The operon is off, bacteria will primarily utilize glucose, as it inhibits the lac operon and prevents lactose metabolism.

If glucose is present but lactose is not

the operon is off due to catabolite repression, as glucose inhibits the utilization of lactose. Bacterial cells will not metabolize lactose because glucose is available.

If lactose is present but glucose is not

The operon is on, allowing bacteria to metabolize lactose as the primary energy source. Lactose is utilized, and the lac operon is activated, enabling the breakdown of lactose into glucose and galactose.

If glucose is lacking and lactose is lacking

The operon is off, as there are no available energy sources for the bacteria to utilize. The bacteria enter a dormant state, conserving resources until conditions improve.

What is the true name for the lac operon activator?

The true name for the lac operon activator is CAP (catabolite activator protein), which enhances the transcription of the lac operon in the presence of lactose.

What is allolactose?

Allolactose is an isomer of lactose that acts as an inducer for the lac operon, binding to the repressor protein and allowing transcription to occur when lactose is present.

In the presence of lactose, allolactose will bind to the lac repressor and inactivates it.

This allows RNA polymerase to transcribe the genes of the lac operon, facilitating the metabolism of lactose. Which means the repressor can’t bind to the operator and inhibit transcription.

In the absence of lactose, allolactose will not be produced and will not bind to the lac repressor.

This allows the lac repressor to bind to the operator, blocking transcription of the lac operon genes.

Constitutive Genes

Genes that are continuously expressed regardless of environmental conditions.