A. Describe in detail the regulation of the prokaryotic lac operon for the following environment: Glucose...
A. Describe in detail the regulation of the prokaryotic lac operon for the following environment: Glucose is present, lactose present, & the repressor protein is mutated such that the allosteric site is non-functional and can no longer bind its substrate. Be sure to specify the presence or absence and location of Lac I, allolactose, cAMP, CAP, and RNA polymerase.
B. Indicate whether transcription is occurring at a basal level, a high level, or not at all.
Homework Answers
A.
The Prokaryotic Lac Operon is controlled by the concerted effect of Lac Repressor, a repressor of the Lac Operon and Catabolite Activator Protein(CAP), a transcriptional activator of Lac Operon.
In an environment where Glucose is present, Lactose is present and Repressor Protein is mutated such that the allosteric site is non-functional and can no longer bind its substrate.
In such an environment, since Glucose is present, cAMP levels are low. Therefore, the affinity of CAP to bind to DNA is also low. Therefore CAP remains unbound to DNA and it does not recruit any RNA Polymerase to the Lac Promoter.
Since Lactose is present, some of it is converted to Allolactose, which normally binds to the Lac Repressor. However, since Lac Repressor is mutated in its Allosteric site, it cannot bind to Allolactose. In wild type Lac repressor, Allolactose binding relieves the repression of the Lac Operon by Lac Repressor Protein. Here, however, Allolactose will remain unbound to Lac Repressor.
Since Lac Repressor is bound to the operator site, it inhibits transcription of the Lac Operon structural genes by RNA Polymerase.
B.
In this environment, no transcription takes place, because:
- CAP is not bound upstream of the Lac Promoter due to low cyclic-AMP levels. Therefore, RNA Polymerase is not actively recruited to the Lac Promoter.
- Lac Repressor is bound to the Lac Operator as Lac Repressor cannon bind to Allolactose (as a consequence of a mutated allosteric site). Thus, the Lac Repressor protein is functioning to inhibit transcription of the Lac Operon
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A. Describe in detail the regulation of the prokaryotic lac
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26. The lac operon in E. coli consists of genes that code for enzymes necessary for the breakdown of lactose. When lactose is absent, the operon is inactive because a repressor protein binds to a specific site in the lac operon. When lactose is present, lactose molecules bind to the repressor protein, causing the repressor protein to dissociate from the binding site. In the absence of glucose (a preferred energy source for bacteria), the protein CAP binds to a regulatory...
5. Jacob, Monod, and Pardee used various E.coli mutants to help determine how the lac operon is regulated. The descriptions of some of the mutants are listed. For each E. coli mutant determine if the lac operon would be on or off in a lactose-only environment. laci mutant: This mutant produces a super repressor that is not inactivated by allolactose. It will still stick. Operater will be off, lacO mutant: This mutant has an altered operator sequence so that the...
gene regulation of bacteria operon systems. Protected View . Saved to this PG References Mailings Review View Help Tell me what you want to do ernet can contain viruses. Unless you need to edit, it's safe to stay in Protected View Enable Editing 5. What happens if lactose levels are low? Put the following list in order (1-5). RNA polymerase is blocked from transcribing the genes for the lactose metabolizing enzymes When RNA polymerase binds to the promoter, it cannot...
The gene machine program shows you what happens when lactose is present in E. coli, and how the lac operon is under negative control. However, the lac operon is also under positive control from a protein called CRP, eAMP Receptor Protein. The absence of the lac repressor is essential but not sufficient for effective transcription of the lac operon. RNA polymerase also depends on the presence of CRP. Like the lac repressor, which can bind to the DNA and lactose....
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