Required information Read the overview and complete the interactivities that fol

Question

Required information Read the overview and complete the interactivities that follow The lac operon consists of a series of genes involved in the breakdown of lactose. The expression of the operon is controlled by two regulatory proteins, a repressor and an activator. Together these two regulatory proteins allow the cell to regulate gene expression in response to the levels of glucose and lactose available to the cell. The following questions relate to the lac operon 1. The Lacl gene makes a repressor protein. True 2. The structural proteins encoded by the lac operon are involved in lactose synthesis. True 9 3. The CAP protein is an activator that binds to the operator. True 4. The product of Lacl is an allosteric protein that can undergo a conformational change when allolactose binds to it. True 5. CAP binding causes the DNA to bend facilitating RNA polymerase binding. True

Explanation / Answer

Answere : Lac operon regulate gene expression in response to the level of gucose and lactose available to the cell.

I. At the level of lactose : It is regulated via negative inducible system. Lac operon posses structural genes. the structural proteins encoded by the lac operon are involved in lactose synthesis.  A regulator gene i.e. LacI is present upstream to the structural genes. The LacI gene makes a represser protein. During absence of lactose, It bind to the operator site and inhibit transcription of structural genes. When lactose is present, some of it convert into allolactose. The product of LacI is an allosteric protein that can undergo a conformational change when allolactose bind to it. These changes causes an inactive repressor protein and this protein will not bind to operter site. This leads to transcription of structural gene and formation of lactose.

At the level of glucose : When glucose is available, genes that participate in metabolism of other sugars are repressed (e.g. lactose metabolism). This phenomenon is called catabolite repression. Catabolite Activator Protein(CAP) along with cAMP, bind to the site near to the promoter and stimulate the binding of RNA polymerase. CAP protein is an activator that bind to the operator. CAP binding causes the DNA to bend faclitating RNA polymerase binding. Cellular level of cAMP are controlled by glucose, a low glucose level increases the abundance of cAMP and enhance the transcription of lac structural gene.

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