Download Control of Gene Express in Prokaryotes

The Genetics of Viruses and
Bacteria: Operons
• Regulation of enzyme activityfeedback inhibition
• Regulation of gene expression
Operons-the basic concept
• Regulated genes can be switched on and
off depending on the cell’s metabolic
needs
• Operon-a regulated cluster of adjacent
structural genes, operator site, promotor
site, and regulatory gene(s)
Operon
• Structural gene-gene that codes for a
polypeptide
• Promoter region-controls access to the
structural genes, located between the
promoter and structural genes, contains
the operator site.
• Operator Site -region where the repressor
attaches
• Regulatory genes-codes for repressor
proteins
• Polycistronic mRNA-transcript for several
polypeptides
Repressible vs. Inducible Operons
two types of negative gene regulation
Repressible
Operons
• Genes are initially
ON
• Anabolic pathways
• End product
switches off its
own production
Inducible Operons
• Genes are initially
OFF
• Catabolic
pathways
• Switched on by
nutrient that the
pathway uses
trp: a repressible operon
lac: an inducible operon
An example of positive gene
regulation-cAMP
• cAMP exerts
positive control
• Binds to promoter,
stimulating
transcription
• Dependent on
glucose
concentration