Where does the active repressor bind?
A repressor is a protein that turns off the expression of one or more genes. The repressor protein works by binding to the gene’s promoter region, preventing the production of messenger RNA (mRNA).
What is the function of lac Z?
The LacZ protein codes for an enzyme called β-galactosidase, which is an essential part of the metabolism of lactose. It cleaves (separates) a single disaccharide lactose molecule into far more digestible glucose and galactose.
What molecule binds to the allosteric site of the repressor?
The tryptophan is able to bind to a site on the allosteric repressor protein, changing its shape and enabling it to interact with the operator region. Once the repressor binds to the operator, RNA polymerase is unable to get beyond the operator and transcribe the genes for tryptophan biosynthesis.
What is the binding site of the repressor?
Repressors can also have two binding sites: one for the silencer region and one for the promoter. This causes chromosome looping, allowing the promoter region and the silencer region to come in proximity of each other.
What activates the repressor?
Repressor. When an amino acid is present, it associates with the met repressor, and the repressor is activated. When tryptophan is not present in the cell, the repressor by itself does not bind to the operator; therefore, the operon is active and tryptophan is synthesized.
What is the function of β-galactosidase?
β-Galactosidase has three enzymatic activities (Fig. 1). First, it can cleave the disaccharide lactose to form glucose and galactose, which can then enter glycolysis. Second, the enzyme can catalyze the transgalactosylation of lactose to allolactose, and, third, the allolactose can be cleaved to the monosaccharides.
What are lac and Trp operons?
What is the difference between Lac operon and Trp operon? Lac operon is involved with the catabolic process of a sugar, but Trp operon is involved in the anabolic process of an amino acid. Lac operon gets activated in the presence of lactose, but Trp operon gets deactivated in the presence of tryptophan.
What is the difference between an allosteric site and an active site?
The allosteric site is a site that allows molecules to either activate or inhibit (or turn off) enzyme activity. It’s different than the active site on an enzyme, where substrates bind. When allosteric activators bind to the allosteric site, the enzyme binds the substrate better, and the reaction becomes faster.
What is the inducer molecule in the lac operon?
The inducer in the lac operon is allolactose. If lactose is present in the medium, then a small amount of it will be converted to allolactose by a few molecules of β-galactosidase that are present in the cell. Allolactose binds to the repressor and decreases the repressor’s affinity for the operator site.
When the repressor is active is the operon on or off?
Repressors and Activators are proteins that bind to DNA and control transcription. Lactose absent, repressor active, operon off. The lac repressor is innately active, and in the absence of lactose it switches off the operon by binding to the operator.
Where are the two binding sites of a repressor located?
Repressors can also have two binding sites: one for the silencer region and one for the promoter. This causes chromosome looping, allowing the promoter region and the silencer region to come in proximity of each other. The lacZYA operon houses genes encoding proteins needed for lactose breakdown.
How does a repressor inhibit the expression of a gene?
Repressor. In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA.
How does a repressor stop the manufacture of lactase?
The repressor will then bind to the operator, stopping the manufacture of lactase. In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers.
What happens when RNA polymerase binds to a repressor?
RNA polymerase then can transcribe the message (expressing the gene). A co-repressor is a molecule that can bind to the repressor and make it bind to the operator tightly, which decreases transcription. A repressor that binds with a co-repressor is termed an aporepressor or inactive repressor.