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The lac Operon Laboratory

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The lac Operon Laboratory Purpose: Learning to analyze an example of gene expression Example: lac operon Type of control: negative inducible The Laboratory Worksheet ... – PowerPoint PPT presentation

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Title: The lac Operon Laboratory


1
The lac Operon Laboratory
Purpose Learning to analyze an example of gene
expression Example lac operon Type of control
negative inducible
2
The Laboratory Worksheet asks How do mutations
affect gene expression of the lac operon?
3
Review Lac Operon
4
Mutations and gene expressio of lac operon
5
Oc mutation a cis acting mutation
6
I- mutation a trans acting mutation
7
Is mutation a trans acting mutation
8
Lab 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.

9
Try 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
-
1

2
3
4
5
6
7
8
9
11
The End.
12
Laboratory Exercise
13
Try out your ability to reason through the
questions.
14
PROTEIN 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
15
The next slides are a key to the mutations.
16
Experimental 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!

17
Experimental 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
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