Regulation of Gene
Expression
Eukaryotic Transcriptional Level
Hormones act as second messengers and pass through the plasma membrane to bind to
and activate transcription factors
Activated transcription factors bind to a promoter region on a chromosome near a gene
Transcription factors aid or inhibit RNA polymerase in binding to the promoter region
and beginning transcription
Prokaryotic Transcriptional Level
Lactose Absent
o Regulator gene codes for a repressor protein
o Repressor binds to operator region (LacO)
o RNA polymerase cannot bind to the promoter region so cannot begin
transcription
o Structural genes are inactive which conserves amino acids
Lactose Present
o Lactose acts as an inducer and binds to the repressor molecule
o Repressor-Inducer complex cannot bind to the operator region (LacO)
o RNA polymerase binds to the promoter region and begins transcription
o LacY codes for lactose permease which makes the membrane more permeable to
lactose, so lactose enters the cell
o LacZ codes for β-galactosidase which hydrolyses lactose into glucose and
galactose for respiration
Expression
Eukaryotic Transcriptional Level
Hormones act as second messengers and pass through the plasma membrane to bind to
and activate transcription factors
Activated transcription factors bind to a promoter region on a chromosome near a gene
Transcription factors aid or inhibit RNA polymerase in binding to the promoter region
and beginning transcription
Prokaryotic Transcriptional Level
Lactose Absent
o Regulator gene codes for a repressor protein
o Repressor binds to operator region (LacO)
o RNA polymerase cannot bind to the promoter region so cannot begin
transcription
o Structural genes are inactive which conserves amino acids
Lactose Present
o Lactose acts as an inducer and binds to the repressor molecule
o Repressor-Inducer complex cannot bind to the operator region (LacO)
o RNA polymerase binds to the promoter region and begins transcription
o LacY codes for lactose permease which makes the membrane more permeable to
lactose, so lactose enters the cell
o LacZ codes for β-galactosidase which hydrolyses lactose into glucose and
galactose for respiration
