DNA and Genetics

Regulator gene regulates the expression of structural genes by its protein products that are mostly transcription factors. These transcription factors bind to the operator region which is located just upstream the binding site of the RNA polymerase and hence prevent the binding and transcription; option D is correct. Operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as repressor protein binding site; option B is wrong. Genes which govern more or less same trait or perform same role are called redundant genes; presence of these genes confers advantage of diluting the effect of point mutation on organisms; option C is wrong. Presence of more than one allele on a genetic locus is called gene polymorphism provided that the allele is present with more than 5% frequency in the population; option A is wrong. 

An operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create monocistronic mRNAs that are translated separately. Regulator gene regulates inhibiting transcription of mRNA.

An operon is a cluster of genes under the control of a single promoter, functioning as a regulated unit of genetic material in prokaryotes.

The tryptophan operon is a repressible operon, meaning it is normally active and is turned off when the end product (tryptophan) is present in sufficient quantities.

The regulator gene (or regulatory gene) is the part of the operon system that codes for the repressor protein.

In the operon model, the operator is the gene segment to which a repressor binds. This prevents the RNA polymerase from transcribing certain genes in the operon unit.

Lac repressor is part of the regulatory network of the lac operon. Lac repressor controls the production of three proteins produced from the gene and affecting the metabolism of lactose. This repressor molecule is a tetramer whose all the subunits are identical. This tetramer binds to a particular region in the bacterial DNA called the operator. This region is present next the three lactose metabolizing proteins. Binding of the repressor to operator causes the block in the production of protein. Otherwise, for three genes to transcribe the repressor protein binds to the lactose molecule and hence unable to bind to operator allows the genes to transcribe.

When E. coli is moved from glucose to a lactose-containing medium, the lac operon is induced to produce enzymes necessary for lactose metabolism.

In a repressible operon, the corepressor binds to the inactive aporepressor to form an active repressor complex that can bind to the operator.

In the lac operon, the active repressor protein binds to the operator site, physically blocking RNA polymerase from transcribing the structural genes.

An operon system typically includes the regulator gene, promoter, operator, and the structural genes it controls.

The lac operon is a classic example of an inducible operon, meaning it is typically turned off but can be activated (induced) by the presence of lactose. Repressible operons, by contrast, are typically on and turned off by the presence of a product.

An operon is a functional unit of DNA in prokaryotes consisting of a cluster of genes under the control of a single promoter and operator, allowing for the coordinated regulation of a metabolic pathway.

Inducible operons are typically in an 'off' state due to the presence of a repressor protein bound to the operator. They are turned 'on' only when an inducer molecule binds to the repressor, preventing it from binding to the DNA.

The regulator gene in an operon system codes for a repressor protein, which is responsible for binding to the operator site to inhibit transcription of the structural genes.