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MCAT TOPIC REVIEWS & RESOURCES

Biological and Biochemical Foundations of Living Systems

BIO
Control of Gene Expression in Prokaryotes

Operon Concept, Jacob-Monod Model

The Operon Concept is a description of a unit of genetic regulation that is the hallmark of the Jacob-Monod Model, which identifies and conceptually organizes the parts of prokaryotic gene expression as an operon.

An operon is responsible for the expression and regulation of a specific mRNA transcript. To perform this job, it consists of a promoter, an operator, and the genes to be transcribed.

Gene repression in bacteria

An operator is a regulatory region that is regulated by the binding of a repressor protein. When a repressor protein is active and binds to an operator, transcription for the associated genes is blocked, a process of gene repression.

Positive control in bacteria

Alternatively, other regulatory proteins can exert positive control by binding to regions of the DNA in a manner that activates the promoter region, thereby inducing the association of transcription factors and RNA Polymerase to form a transcription initiation complex.

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