Gene Regulation and the Lac Operon

The process of converting a gene's information into a functional product, typically a protein.

A DNA sequence where RNA polymerase binds to initiate transcription.

Regulatory protein that binds to DNA and prevents transcription.

Regulatory protein that binds to DNA and stimulates transcription.

A mechanism where transcription is controlled by the binding of a repressor protein to the operator, preventing gene expression.

A mechanism where transcription is controlled by the binding of an activator protein to the operator, promoting gene expression.

A functioning unit of DNA consisting of a cluster of genes under the control of a single promoter. The genes are transcribed as a single mRNA and translated together.

The lac operon is a group of genes in E. coli bacteria that are involved in the metabolism of lactose.

Lactose is a type of sugar that is made up of glucose and galactose.

When glucose is unavailable, E. coli uses the lac operon to break down lactose for energy.

The lacZ gene encodes β-galactosidase, an enzyme that breaks down lactose into glucose and galactose.

lacY encodes lactose permease, a protein that transports lactose into the cell.

The lacI gene encodes the lac repressor protein, which binds to the operator and prevents transcription when lactose is absent.

The operator is a DNA sequence that the lac repressor protein binds to.

The promoter is a DNA sequence where RNA polymerase binds to initiate transcription.

The repressor protein undergoes a conformational change when lactose binds, releasing it from the operator.

A protein that helps activate the transcription of certain genes in the presence of low glucose levels.

A cyclic nucleotide that acts as a signal molecule, regulating various cellular processes, including transcription.

An enzyme that converts ATP to cAMP, influencing the levels of cAMP in the cell.

When glucose is present, E. coli prioritizes its use, leading to low transcription of the lac operon, as CAP is inactive, preventing activation.

When lactose levels are high, but glucose is low, the lac operon is highly transcribed as CAP is active and the repressor is inactive, allowing lactose metabolism.

When lactose is absent, transcription of the lac operon is blocked, regardless of glucose levels, as the lactose repressor binds to the operator.

The tryptophan operon in E. coli is an example of a repressible operon, meaning gene expression is repressed in the presence of its product, tryptophan.

The inactive repressor in the tryptophan operon undergoes a conformational change upon tryptophan binding, enabling it to bind to the operator and inhibit transcription.

A repressor protein is a molecule that binds to a specific DNA sequence called the operator, preventing the expression of the genes in an operon. This binding hinders the activity of RNA polymerase, the enzyme responsible for transcription.

Allolactose is a modified form of lactose that acts as an inducer for the lac operon. It binds to the repressor protein, causing a change in its shape and preventing it from binding to the operator, allowing transcription to occur.

Negative control refers to the regulation of gene expression where a repressor protein blocks transcription. This means that the operon is usually 'off' and requires a signal, like the presence of an inducer, to turn it 'on'.

Catabolite repression is a mechanism where the presence of glucose, a preferred energy source, suppresses the expression of the lac operon. This happens because glucose inhibits the activity of the catabolite activator protein (CAP), which is needed for optimal transcription of the lac operon.

The catabolite activator protein (CAP) is a regulatory protein that binds to DNA and stimulates transcription of the lac operon when glucose levels are low. It enhances the binding of RNA polymerase to the promoter.

The operator is a specific DNA sequence located in the lac operon where the repressor protein binds. This binding blocks RNA polymerase from initiating transcription.

The inducer is a molecule, like allolactose, that binds to the repressor protein and changes its shape, preventing it from binding to the operator. This allows RNA polymerase to transcribe the genes in the operon.

A promoter is a DNA sequence located upstream of a gene where RNA polymerase binds to initiate transcription. The promoter is the starting point for gene expression.

β-galactosidase is an enzyme encoded by the lac operon that breaks down lactose into glucose and galactose. This process is crucial for metabolizing lactose as a source of energy.