Lac Operon

Sophie Barrett
Mind Map by , created over 5 years ago

An example of prokaryotic gene expression that allows the switching of the metabolite used from glucose (preffered) to lactose.

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Sophie Barrett
Created by Sophie Barrett over 5 years ago
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Lac Operon
1 The product of the Lac Z gene = beta-galactosidase. It cleaves lactose into glucose and galactose
2 The product of the Lac Y gene = lactase permease. It transports lactose into the cell
3 The product of the Lac A gene = beta-galactoside transacetylase. It is also involved in lactose hydrolysis
4 LACTOSE ABSENT
4.1 The path of RNA polymerase is blocked
4.1.1 transcription of the Lac genes cannot occur
4.1.1.1 saves energy, there is no need to have the proteins since lactose is not present
4.1.1.2 Only a few Lac enzymes remain in the cell, but these are crucial
5 LACTOSE PRESENT
5.1 The few Lac enzymes present allow the lactose to be taken up into the cell
5.1.1 These few lactose disaccharide molecules are metabolised
5.1.1.1 One intermediate is allolatose
5.1.1.1.1 Allolatose, an isomer of lactose, acts as an inducer
5.1.1.1.1.1 Binds to the lactose repressor
5.1.1.1.1.1.1 Changes it's confirmation
5.1.1.1.1.1.1.1 Lactose repressor can no longer bind to the operator
5.1.1.1.1.1.1.1.1 The path of RNA Polymerase is no longer blocked
5.1.1.1.1.1.1.1.1.1 Transcription of the Lac genes commences
5.1.1.1.1.1.1.1.1.1.1 Uptake and Metabolism of Lactose from the environment
5.1.1.1.1.1.1.1.1.1.2 So allactose acts an indicator of the presence of the lactose
6 But, if glucose if present, the cell will use it preferentially.
6.1 The cell uses a Catacolic Activator Protein (CAP) to detect available glucose
6.1.1 CAP binds to DNA upstream of the lac promoter
6.1.1.1 This enhances the binding of RNA Polymerase, increasing transcription
6.1.1.2 But, it can CAP can only bind in the presence of cAMP
6.1.1.2.1 cAMP levels are influenced by glucose conentration
6.1.1.2.1.1 How?
6.1.1.2.1.1.1 Adenylyl cyclase cataylses the formation of cAMP and is inhibited by glucose

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