The blob operon produces enzymes that convert compound A...

The blob operon produces enzymes that convert compound A into compound B. The operon is controlled by regulator gene $S .$ Normally, the enzymes are synthesized only in the absence of compound B. If gene $S$ is mutated, the enzymes are synthesized in the presence and in the absence of compound B. Does gene $S$ produce a regulator protein that exhibits positive or negative control? Is this operon inducible or repressible?

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Key Concepts

Operon Model

An operon is a cluster of functionally related genes that are transcribed together from a single promoter in prokaryotes. This arrangement allows for coordinated regulation of the genes involved in a specific metabolic pathway or function, ensuring that they are expressed in concert as needed.

Regulatory Proteins

Regulatory proteins, which can function as repressors or activators, interact with specific DNA sequences near the operon to modulate transcription. Their binding can either inhibit or enhance RNA polymerase’s ability to initiate transcription, thereby controlling gene expression in response to environmental or cellular signals.

Negative Control

Negative control in gene regulation involves a regulatory protein that represses transcription when bound to the operator sequence of an operon. In this mechanism, inactivation or the absence of the repressor permits transcription, whereas its presence blocks transcription, thereby ensuring genes are expressed only when appropriate.

Repressible Operon

A repressible operon is one that is typically active but can be turned off in the presence of a specific molecule, often by the action of a repressor protein. This type of regulatory system generally functions in feedback inhibition, where the accumulation of a product signals the operon to shut down subsequent production.

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