(Genetics) In the Operon Model, the operator is the gene in which a repressor binds. This results in the prevention of the RNA polymerase from binding to it, thus, preventing the expression of certain genes in the operon unit.

What is an “operator” and what function of an Operator in an Operon. An operator is a short segment of DNA where an active repressors will bind. When a repressor is present, it normally binds to the Operator of an Operon and blocks it from being transcribed by RNA Polymerase.

An operon is made up of several structural genes arranged under a common promoter and regulated by a common operator. It is defined as a set of adjacent structural genes, plus the adjacent regulatory signals that affect transcription of the structural genes.

They are the sites in which the regulatory molecule binds to an operon. The key difference between the promoter and the operator is based on the type of molecule that binds to the respective DNA sequence. RNA polymerase binds to the promoter, whereas regulatory molecules of the operon system bind to the operator.

Operons are common in bacteria, but they are rare in eukaryotes such as humans.

A monocistronic operon contains only a single gene, but most genes occur in polycistronic operons encoding multiple genes associated with a related function. A cistron is a DNA segment encoding a polypeptide and genes in a polycistronic operon are jointly regulated.

Glucose present, lactose absent: No transcription of the lac operon occurs. That’s because the lac repressor remains bound to the operator and prevents transcription by RNA polymerase. Also, cAMP levels are low because glucose levels are high, so CAP is inactive and cannot bind DNA.

Bacterial Operons Are Coregulated Gene Clusters Grouping related genes under a common control mechanism allows bacteria to rapidly adapt to changes in the environment. The best-studied examples of operons are from the bacterium Escherichia coli (E.

Lac operon is an example of the inducible operon. Lactose Is a substrate of enzyme beta-galactosidase and Is the Inducer of the lac operon. In the presence of an inducer, repressor becomes inactive. This allows transcription in the operator region, which results in the release of mRNA.

The lac operon is a classic example an inducible operon. When lactose is present in the cell, it is converted to allolactose. Allolactose acts as an inducer, binding to the repressor and preventing the repressor from binding to the operator. This allows transcription of the structural genes.

A repressible operon is one that is usually on but which can be repressed in the presence of a repressor molecule. The repressor binds to the operator in such a way that the movement or binding of RNA polymerase is blocked and transcription cannot proceed. An inducible operon is one that is usually off.

An operon is a unit of the bacterial chromosome consisting of the following components:

• A regulatory gene. The regulatory gene codes for a regulatory protein.
• An operator. The operator is the region of DNA of the operon that is the binding site for the regulatory protein.
• A promoter.
• Structural genes.

 An operon is a group of closely linked structure genes and associated control genes.  The operon consist of regulatory gene,structural gene, operator and promoter site.

The ara operon is regulated by the AraC protein. If arabinose is absent, the dimer AraC protein represses the structural gene by binding to araI1 and araO2 and the DNA forms a loop, which prevents RNA polymerase from binding to the promoter of the ara operon, thereby blocking transcription. This breaks the DNA loop.

Gene Expression  The process by which a gene’s information is converted into the structures and functions of a cell by a process of producing a biologically functional molecule of either protein or RNA (gene product) is made.

The lac, or lactose, operon is found in E. coli and some other enteric bacteria. This operon contains genes coding for proteins in charge of transporting lactose into the cytosol and digesting it into glucose. This glucose is then used to make energy.

β -galactosidase is a structural gene present in segment of DNA, which carry Icdes for the synthesis of protein. Mutation in the lac Ygene of E. coli needs residues of cytoplasmic enzyme β -galactosidase. Lactose permease is a membrane protein, which is a major facilitator superfamily.

The gene Z produces enzyme β-galactosidase for splitting of lactose/galactosidase into glucose and galactose.