Class notes
Lecture Notes on the Lac Operon (MCB2023S)
- Course
- MCB2023S
- Institution
- University Of Cape Town (UCT)
Summary of lecture on the Lac Operon. Contents can be seen on the first page.
[Show more]
Content preview
The Lac OperonTHE LAC OPERON.......................................................................................................................................... 1
THE IMPORTANCE OF MUTATIONS............................................................................................................................2
THE LAC OPERON MODEL.......................................................................................................................................2
What were the Proofs of the Lac operon Model?..........................................................................................2
What is the difference between an Operon and a Regulon?.........................................................................2
Structure:........................................................................................................................................................2
REGULATION OF THE LAC OPERON............................................................................................................................3
Positive regulation:.........................................................................................................................................3
Negative Regulation:......................................................................................................................................3
Catabolite Repression:....................................................................................................................................3
TRANS AND CIS-ACTING CONTROL ELEMENTS.............................................................................................................4
Trans-acting control (via proteins).................................................................................................................4
Cis-acting control elements (DNA Recognition sites).....................................................................................4
INDUCTION OF THE LAC OPERON..............................................................................................................................4
PROOFS........................................................................................................................................................ 4
1. PROOF THAT GENES ARE TRANSCRIBED ON SINGLE MRNA TRANSCRIPT.........................................................................5
Mechanism:....................................................................................................................................................5
2. PROOF THAT ALLOLACTOSE AND NOT LACTOSE IS THE INDUCER...................................................................................5
Recap: Lac Operon Repression & Induction:...................................................................................................5
Experiment 1: Use a lacZ- lacY+ mutant.........................................................................................................6
Experiment 2: Use lacZ- lacY+ mutant............................................................................................................6
3. PROOF THAT LACI ENCODES A REPRESSOR...............................................................................................................6
Results:...........................................................................................................................................................6
4. PROOF OF THE ROLES OF CIS AND TRANS-ACTING ELEMENTS.......................................................................................7
Proof Trans-acting element: Experiment 1.....................................................................................................7
Proof Trans-acting element: Experiment 2.....................................................................................................8
Proof Cis-acting element: Experiment 1.........................................................................................................8
Proof Cis-acting element: Experiment 2.........................................................................................................9
5. PROOF LACI REPRESSOR BINDS TO OPERATOR REGION IN PROMOTOER.........................................................................9
The lac Repressor:...........................................................................................................................................9
Key Features of typical bacterial vector for Protein Production:....................................................................9
LacI Purification Method:.............................................................................................................................10
Gel shift assay:..............................................................................................................................................10
DNAse Foot printing technique:...................................................................................................................10
Findings:.................................................................................................................................................................. 11
6. PROOF THAT LACI BINDS TO INDUCER MOLECULE...................................................................................................12
CATABOLITE REPRESSION............................................................................................................................ 13
Glucose control of cAMP levels:...................................................................................................................13
Control of Adenylate Cyclase Activity:..........................................................................................................13
CAP regulation of Lac operon.......................................................................................................................14
Proof that CAP binds cAMP for positive regulation of lacZ:.........................................................................14
, The Lac Operon
The Importance of Mutations
- Mutations are important tools of genetic analyses.
- Key principles and concepts in genetics have been obtained through analyses of
mutants.
- Mutations allow fundamental biological processes to be dissected so that the overall
biological system can be understood
- A lot of info on lac operon was obtained through study of mutations.
The Lac Operon Model
- Deduced the structure and function of the lac operon using a genetic approach
- Analyzed the interactions of mutations in E. coli that interfered with normal
regulation of the lactose metabolism
- Demonstrated that the operon as the basic unit of transcriptional control in bacteria
o Structural genes (produce structural proteins)
o Regulatory genes (produce regulatory proteins)
o Regulatory DNA sequences (not genes)
What were the Proofs of the Lac operon Model?
- Genes transcribes on single mRNA transcript
- Allolactose and not lactose is the inducer
- lacI encodes a repressor
- Prove roles of cis and trans-acting elements
- LacI binds to Operator region in promoter
- LacI binds to inducer molecule
What is the difference between an Operon and a Regulon?
- Operon:
o Group of genes physically linked to the chromosome under the control of the
same promoter which gives rise to a polycistonic mRNA.
- Regulon:
o Group of genes needed for the same process but located in different parts of
the chromosome and containing their own promoter, but the promoters are
regulated in the same fashion to allow for coordinated expression.
Structure:
- plac = Promoter for structural genes
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through EFT, credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying this summary from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller mattclothier13. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy this summary for R120,00. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
82013 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy summaries for 14 years now