Essay Example on Negative & Positive Control of Lac Operon: CAP-cAMP System

Introduction

The inducer repressor in the control of lac operon, which is an example of the negative control where the expression is blocked. On the other hand, the CAP-cAMP system is one of the examples of the positive control as the expression of the lac operon needs the activation signal, which is, in this case, an interaction of the complex CAP-cAMP that has a CAP region (Phillips et al., 2019). For the activators or the repressors proteins to perform the tasks, they must be in a position to perform and exist in two different states, one which binds the DNA targets and the other that cannot (Jackson, 2017). The connection state should be appropriate for the selected environmental conditions. For the repressor protein, the way regulation of the DNA binding is taken throughout an interaction of the different sites in the three-dimension structures in the protein. DNA-binding is one site of the domain.

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On another site, an allosteric site act as a switch setting the DNA-binding domain in the modes of functional and non-functional. There is an interaction between the allosteric site and the small molecule molecules referred to as allosteric effectors (Phillips et al., 2019). After binding of the by the allosteric effectors, there is a conformational change in the change in the protein regulation that alters the DNA binding domain. Few activators bind to the effectors binding to the DNA. The others will bind DNA only in the absence of the allosteric effector. The bacteria have evolved different strategies by use of different combinations in control experiments in different gene expression regulations.

Cells get more energy from the breakdown of glucose than that of lactose. When they are both present during the synthesis, there is no inclusion of the β-galactosidase in the glucose after metabolization.

Negative control

The lac operon has both positive and negative transcriptional regulation. Negative regulation is easier to understand. The i gene product of the lac operon is a protein called lac repressor, which is a macromolecular repressor binding the lac operator and blocking RNA polymerase from binding and thereby blocking transcription (Jackson, 2017). Negative regulation occurs by the introduction of an inducer that activates the synthesis of the gene products that are involved in catabolism by the removal of a barrier to the transcription.

Positive control

The positive control of the lac operon, the lactose promoter, differs from ideal -35 and -10 sequences that do not function efficiently by self-stimulation transcription as RNA polymerase does not bind well. There is a positive activator protein known as CRP or the Cyclic AMP Protein that binds specific sequences adjacent to the promoter assisting RNA polymerase in binding to the promoter (Phillips et al., 2019). For the function to stimulate the RNA polymerase that binds to the lac promoter, the CRP must bind to AMP. It, therefore, undergoes conformational changes, which greatly increase the affinity for some DNA sites, including one in the lac operon adjacent to the RNA polymerase binding site.

Advantages

One of the advantages of the lac operon is the use of E. coli in experimental and industrial purposes. LacZ gene encoded the β- galactose and used as a reporter in the prokaryotic and eukaryotic systems (Phillips et al., 2019). It is one of the reliable reporter systems in tracking and monitoring the products of lacZ genes (Stefanski et al., 2016). However, it also has limitations. Although the system is suitable in the qualitative analysis of gene expression, the product needs to have further experimental procedures such as lysate preparation. Therefore the system is unsuitable for high throughput screening.

References

Jackson, R. C. (2017). The Boolean kinetics of signal transduction. Bioinformatics, 24(18), 2044-2050. https://www.researchgate.net/profile/Robert_Jackson18/publication/320908715_The_Boolean_Kinetics_of_signal_transduction/links/5a01d5ac0f7e9bfd74604d69/The-Boolean-Kinetics-of-signal-transduction.pdf

Phillips, K. N., Widmann, S., Lai, H. Y., Nguyen, J., Ray, J. C. J., Balázsi, G., & Cooper, T. F. (2019). Diversity in lac operon regulation among diverse Escherichia coli isolates depends on the broader genetic background but is not explained by genetic relatedness. mBio, 10(6). https://mbio.asm.org/content/mbio/10/6/e02232-19.full.pdf

Stefanski, K. M., Gardner, G. E., & Seipelt-Thiemann, R. L. (2016). Development of a lac operon concept inventory (LOCI). CBE—Life Sciences Education, 15(2), ar24. https://www.lifescied.org/doi/pdf/10.1187/cbe.15-07-0162