Lac Operon Flashcards
What is an operon?
Group of genes under control of same regulatory mechanism + expressed at same time.
Why are lac operons good?
Efficient way of saving resources
Genes not involved in production = switched off.
Define structural genes:
Proteins NOT involved in DNA regulation.
In lac operon = enzymes that metabolise lactose
What are the structural genes in the Lac operon?
lacZ = B-galactosidase = lactose = glucose + galactose
lacY = lactose permease = facilitates passage of lactose across phospholipid bilayer
lacA = transacetylase
What are regulatory genes?
Proteins involved in DNA regulation.
lac I = Codes for repressor protein
Upstream
What is the operator?
DNA sequence where repressor protein binds to
What is the promoter?
Binding site of RNA polymerase.
What happens when glucose is present and no lactose is present?
LacI = expressed to make repressor protein
Binds to operator –> blocks promoter (RNA polymerase binding site)
No transcription of 3 structural genes
What happens when there is glucose + lactose present?
Lactose binds to repressor protein
Conformational change
Repressor no longer bind to operator unblocking promoter
Transcription of structural genes occur –> at slow rate
What happens when only lactose is present?
CRP (receptor protein) binds to cAMP
Increases when there is no glucose
Complex bind to RNA polymerase to upregulate activity.
Increases quantity of enzymes to metabolise lactose efficiently.
