Title: The lac Operon Laboratory
1The lac Operon Laboratory
Purpose Learning to analyze an example of gene
expression Example lac operon Type of control
negative inducible
2The Laboratory Worksheet asks How do mutations
affect gene expression of the lac operon?
3Review Lac Operon
4Mutations and gene expressio of lac operon
5Oc mutation a cis acting mutation
6I- mutation a trans acting mutation
7Is mutation a trans acting mutation
8Lab Worksheet Haploid and Heterozygous Diploid
Mutants
- Predict if you expect to obtain
- transcription/translation of the lacZ and lacY
genes when lactose is absent or present for the
E.coli.
9Try out your ability to reason through the
questions.
10?-galactosidase Permease
Lactose No lactose Lactose
IPOZY -
I-POZY
IP-OZY
IPOcZY
IPOZ-Y-/ I-POZY
IPOcZY-/ IPOZ-Y
IPOcZ-Y/ I-POZY-
ISPOZY-/ I-POZ-Y
IP-OcZY/ IPOZ-Y-
No Lactose
-
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11The End.
12Laboratory Exercise
13Try out your ability to reason through the
questions.
14PROTEIN PRODUCT ?-galactosidase Permease
Lactose No lactose Lactose
IPOZY -
I-POZY
IP-OZY
IPOcZY
IPOcZY-/ IPOZ-Y
IPOcZ-Y/ I-POZY-
ISPOZY-/ I-POZ-Y
IP-OcZY/ IPOZ-Y-
No Lactose
-
IPOZ-Y-/ I-POZY
15The next slides are a key to the mutations.
16Experimental tests on the repressor
- I cells synthesize full levels of the lac
enzymes only in the presence of an inducer - I- mutations NO DNA BINDING ACTIVITY,
TRANSCRIPTION OCCURS EVEN IN ABSENCE OF INDUCER! - Is mutation NO LACTOSE BINDING ACTIVITY but has
DNA BINDING ACTIVITY. NO TRANSCRIPTION EVEN WITH
INDUCER!
17Experimental mutations to the repressor
I sinducer binding region mutated Inhibits
transcription, even with inducer
Lactose binding site
DNA binding site
I - DNA binding site mutated, prevents
binding, allows transcription