What does it mean when we say that a gene is controlled bytranscriptional contro

Question

What does it mean when we say that a gene is controlled bytranscriptional control? Distinguish between constitutive genes and inducible genes andbe able to diagram an example of each of these controlsystems? What is the role of a promotor , repressor and operator in theexpression of inducible and repressible genes? How do these twotypes of genes differ from one another? What does it mean when we say that a gene is controlled bytranscriptional control? Distinguish between constitutive genes and inducible genes andbe able to diagram an example of each of these controlsystems? What is the role of a promotor , repressor and operator in theexpression of inducible and repressible genes? How do these twotypes of genes differ from one another?

Explanation / Answer

                     Ingeneral gene expression is under the control of transcriptionfactors.       So when we say that a geneis under transcription control , what it means is thatthe particular gene expression is       controlled by certaintranscription factors.
      Constitutive Genes       A gene that is transcribedat a constant level inspite of the environmental conditions of thecell are known as constitutive       genes.       These genes encode aproduct which is required in the normal mainatince of the basiccellular processess.       These are also known ashousekeeping genes, that are continuously expressed without anyregulation and are       expressed at low levels inall cells.       Example : The genes thatare responsible for the production of keratin in nails andhair.       Induciblegenes.       Under particular molecularconditions the gene products that increase in concentration areknown as inducible genes.       Under particular molecularconditions the gene products that increase in concentration areknown as inducible genes.       These are the genes whichcauses the induction of gene expression when it is requiredby th ecell.       Unlike constitutive genes,inducible genes are not expressed at all conditions.       Example : When there isdamage to the DNA there is expression of genes that encode for DNArepair.              Role ofPromotor. .       A promotor is the regionon DNA where the mechanism of transcription is initiated.       It is a sequence of DNAwhich enables a gene to be transcribed and is recognosed by RNApolymerase.       When RNA polymerase bindsto the promoter region it can allow theexpression of either the inducible gene and       repressible gene.       The promotor region on DNAis represented as p.              Role ofRepressor:       The genes that decrease inconcentration in response to molecular signals are known asrepressible genes.       The genes that decrease inconcentration in response to molecular signals are known asrepressible genes.       The repressor geneproduces the repressor protein .which has the ability to bind tothe operator and switches off the       expression of thestructural genes associated with that operon.       In simple terms it is agene that prevents transcription.       When the repressor genesynthesises the repressor protein and it binds to the operator thenthe expression of the gene       is stopped.       This is generallyrepresented as i       Role ofoperator.       An operator is asegment of DNA to which the regulatory proteinbinds.       Either a repressoror an ativator can bind to the operator.       If a repressorbinds to the operator , the expression of the gene isprevented , while the binding of an activator to the       operator regioncauses the gene to be expressed.       This operator isrepresented by o.              The inducible andthe repressor genes differ markedly from each other.       An inducible gene causes the gene to beexpressed while arepressible gene prevents the expression of thegene.
      Hope this helpsyou.       An operator is asegment of DNA to which the regulatory proteinbinds.       Either a repressoror an ativator can bind to the operator.       If a repressorbinds to the operator , the expression of the gene isprevented , while the binding of an activator to the       operator regioncauses the gene to be expressed.       This operator isrepresented by o.              The inducible andthe repressor genes differ markedly from each other.       An inducible gene causes the gene to beexpressed while arepressible gene prevents the expression of thegene.

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