Lac Operon

Lac Operon

The product of the Lac Z gene = beta-galactosidase. It cleaves lactose into glucose and galactose
The product of the Lac Y gene = lactase permease. It transports lactose into the cell
The product of the Lac A gene = beta-galactoside transacetylase. It is also involved in lactose hydrolysis
LACTOSE ABSENT
1. The path of RNA polymerase is blocked
  1. transcription of the Lac genes cannot occur
    1. saves energy, there is no need to have the proteins since lactose is not present
    2. Only a few Lac enzymes remain in the cell, but these are crucial
LACTOSE PRESENT
1. The few Lac enzymes present allow the lactose to be taken up into the cell
  1. These few lactose disaccharide molecules are metabolised
    1. One intermediate is allolatose
      1. Allolatose, an isomer of lactose, acts as an inducer
        Binds to the lactose repressor
        Changes it's confirmation
        Lactose repressor can no longer bind to the operator
        The path of RNA Polymerase is no longer blocked
        Transcription of the Lac genes commences
        Uptake and Metabolism of Lactose from the environment
        So allactose acts an indicator of the presence of the lactose
But, if glucose if present, the cell will use it preferentially.
1. The cell uses a Catacolic Activator Protein (CAP) to detect available glucose
  1. CAP binds to DNA upstream of the lac promoter
    1. This enhances the binding of RNA Polymerase, increasing transcription
    2. But, it can CAP can only bind in the presence of cAMP
      1. cAMP levels are influenced by glucose conentration
        How?
        Adenylyl cyclase cataylses the formation of cAMP and is inhibited by glucose

Nächster

Beschreibung

Zusammenfassung der Ressource

ähnlicher Inhalt

	Erstellt von Sophie Barrett vor mehr als 10 Jahre