the lac operon - mercer county community college - mccc - west
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No Slide TitleE. coli and other bacteria
Bacterial Genes
Can be turned on, or off depending on cell needs
Operon
1 promoter for a number of genes
Polycistronic mRNA
2
3
BUT, if lactose is used instead:
convert lactose to glucose and galactose
4
coordinate gene expression
5
Lac Z gene encodes betagalactosidase
b-gal
Add lactose 3,000 molecules of bgal
6
7
So…………………..
inducer
8
C. operator = must be unbound for P to be
“open”
9
Lac Y gene encodes permease that transports lactose into cell
Lac A encodes a transacetylase
10
Is lactose PRESENT or ABSENT?
12
In trans?
Its normally repressed! = OFF
Because lactose is absent
When lactose is present
conformational change
16
5. Cell metabolizes lactose
Binds repressor protein causing a conformational change
•
No lactose:
Mutant Mutant Phenotype
24
lactose?
In presence of lactose?
of lactose?
In presence of lactose?
F’ I+ Inducible?
I+P+O+Z- Y+A+
29
Inducible?
30
cannot move
Bacterial Genes
Can be turned on, or off depending on cell needs
Operon
1 promoter for a number of genes
Polycistronic mRNA
2
3
BUT, if lactose is used instead:
convert lactose to glucose and galactose
4
coordinate gene expression
5
Lac Z gene encodes betagalactosidase
b-gal
Add lactose 3,000 molecules of bgal
6
7
So…………………..
inducer
8
C. operator = must be unbound for P to be
“open”
9
Lac Y gene encodes permease that transports lactose into cell
Lac A encodes a transacetylase
10
Is lactose PRESENT or ABSENT?
12
In trans?
Its normally repressed! = OFF
Because lactose is absent
When lactose is present
conformational change
16
5. Cell metabolizes lactose
Binds repressor protein causing a conformational change
•
No lactose:
Mutant Mutant Phenotype
24
lactose?
In presence of lactose?
of lactose?
In presence of lactose?
F’ I+ Inducible?
I+P+O+Z- Y+A+
29
Inducible?
30
cannot move