47. Regulation of Gene Expression in Prokaryotes ; The Operon Model
Explains the operon as a prokaryotic gene cluster under one promoter, defining its promoter, operator, structural genes and regulator gene. Contrasts inducible operons, illustrated by the Lac operon, with repressible operons, illustrated by the Trp operon, and then outlines eukaryotic gene regulation at the DNA, transcription, translation and post-translational levels. Ends with four multiple-choice questions and their answers.
Topic 47 of 70 in the MU Sofia syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 7 sections, about 600 words (4 min of reading), with 10 flashcards.
In this note
Introduction
Regulation of Gene Expression in Prokaryotes ; The Operon Model
Types of Operons
Regulation of Gene Expression in Eukaryotes
Post-translational Regulation
MCQs
Answers
Regulation of Gene Expression in Prokaryotes ; The Operon Model
Definition: An operon is a cluster of genes under the control of a single promoter, found in prokaryotes.
Components:
Promoter: The region where RNA polymerase binds to start transcription.
Operator: A segment of DNA that a repressor binds to, inhibiting transcription.
Structural Genes: Genes that are co-transcribed into a single mRNA strand.
Regulator Gene: Produces a repressor or activator protein that controls the operon.
Types of Operons
Inducible Operons:
Example: Lac Operon in E. coli.
Function: Usually off but can be turned on (induced) when a specific molecule (inducer, e.g., lactose) is present.
Mechanism: The repressor protein binds to the operator to prevent transcription. The inducer binds to the repressor, changing its shape and detaching it from the operator, allowing transcription.
Repressible Operons:
Example: Trp Operon in E. coli.
Function: Usually on but can be turned off (repressed) when a specific molecule (corepressor, e.g., tryptophan) is present.
Mechanism: The repressor is inactive alone but becomes active when bound to the corepressor, allowing it to bind to the operator and block transcription.
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