Question

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Describe transcription and translation in bacteria. How is gene regulation in bacteria achieved? What is the two component system of regulation? Give some examples of negative and positive regulation. How do the sensor and response proteins get activated?

Answer 1

Transcription and translation in bacteria:

Positive and negative regulation of genes:

If the genes of an operon are expressed always except in the presence of a repressor protein, it is known as negative regulation. Means, if the repressor is inactivated, the operon can be expressed constitutively.

If the genes are expressed only in the presence of regulatory proteins, it is said to be under positive regulation, means in the absence of positive regulatory protein, the gene remains turned off.

Lac operon – negative regulation:

The operon is a functioning unit of genomic DNA (deoxyribonucleic acid), which is a group of genes whose transcription is under the control of a single promoter. The “lac Operon” contains the genes that code for lactose metabolizing proteins of E. coli. Lactose is an inducer molecule of lac operon, when inducer binds to the repressor, its shape is altered, in this state; the operator cannot bind to the repressor.

The operator is a part of an operon, which is a DNA binding site for a repressor, binding of the repressor to the operator site terminates the process of transcription in prokaryotes. Repressor has two binding sites for operator and inducer respectively.

So, the RNA polymerase binds to the promoter site, thus initiating transcription of lac operon genes that result in the synthesis of proteins essential for lactose metabolism. If lactose is not present, the operator binds to the repressor and prevents transcription (when glucose is present, lac operon is turned off).

Trp operon – positive regulation:

The “trp operon” acts through “operator-repressor mechanism” and thus represses the transcription. In this, the synthesis of excessively synthesized proteins can be turned off. The repressor molecule (excessively synthesized molecule) must bind to the coreceptor molecule (buy product or end product of repressor). Then, the coreceptor activates the repressor protein, which binds to the operator site.

For example, tryptophan is an amino acid, and if it is excessively synthesized by the organism, it controls its transcription through “trp Operon.” In this, the tryptophan (corepressor) binds to the repressor protein and makes it get activated. This activated repressor now binds to the operator site, and prevents the binding of RNA polymerase enzyme, thereby inhibiting the protein synthesis.