Prokaryotic Gene regulation

1. Gene Action and Regulation
Khirood Doley (PhD)
LAC OPERON

2. The Operon concept was given by
Francois Jacob and Jacques
Monod in 1961
An operon is coordinated unit of
gene regulation
They usually control an important
biochemical process
They are only found in
prokaryotes
Operon

3. 1. What is a Gene?
2. What is Operon – Differences between prokaryotic and
eukaryotic gene expression?
3. What is Lac operon? Structural Genes of Lac operon?
4. Lac operon regulation – How it works?
3
Key points

4. 4
• DNA encodes
for cell
1. Gene
DNA

5. 5
• Sequence of nucleotides in DNA or RNA that
codes for a molecule that has a function

6. 6
E. coli
m-RNA in prokaryotes are POLYCISTRONIC i.e.
under one promoter multiple genes are present
m-RNA information is changed into actual
protein
Genes are transcribed into m-RNA

7. 7
2. Differences between prokaryotic and eukaryotic gene expression
Prokaryotic mRNA

8. Eukaryotic cell
eukaryotic mRNA

9. 3. What is Lac operon?
Lactose can be an excellent meal for E. coli bacteria
However, they'll only gobble up lactose when other, better
sugars – like glucose – are unavailable
With that context, the lac operon is an operon, or group of
genes which encodes proteins, allowing bacteria to use
lactose
3. What is Lac operon ?

10. 10
3. Structural Genes of Lac operon?

12. 1. Negative regulation:
Glucose present Lactose absent
2. Positive regulation:
Glucose absent Lactose present
 Lac repressor
 Catabolite activator protein (CAP) and cAMP
4. The Lac operon regulation
Role

13. 1. Negative regulation: NO TRANSCRIPTION

14. Permease
Lactose
Glucose absent Lactose present
Leaky Operon
2. Positive regulation: TRANSCRIPTION occurs

15. When lactose enters cell, a small
amount is converted into
Allolactose via β-galactosidase

16. Allolactose binds to lac
repressor rendering repressor
inactive and cannot bind to
OPERATOR

17. In absence of lac repressor on
operator site, RNA Polymerase
binds to promotor

18. Story continue…..

19. RNA Pol. alone can’t bind to promoter unless it gets extra help from
CAP which binds to a region just before lac P and it helps RNA Pol.
with high level of transcription
CAP
site
CAP

20. • cAMP regulates CAP
• cAMP is hunger signal by E. coli
CAP
CAPcAMP

22. Structure of cyclic adenosine
monophosphate (cAMP)
The presence or absence of glucose
affects lac operon by affecting
concentration of cAMP

23. cAMP being synthesized by ATP in
reaction catalyzed by Adenylate cyclase

24. the lac operon really turns on
Two conditions :
• Glucose must be unavailable
• Lactose must be available
Conclusion

25. Glucose Lactose CAP binding
Repressor
binding
Level of
transcription
+ - - +
No
transcription
+ + - -
Low-level
transcription
- - + +
No
transcription
- + + -
Strong
transcription
Summary of lac operon responses

26. Weaver, R.F., 2012. Molecular Biology 5th Ed. New York: McGraw-Hill. pp 914.
Karp, G., 2010. Cell and Molecular Biology: Concepts and Experiments 6th ed. New Jersey: John
Wiley and Sons, Inc. pp 837.
Brooker, R.J., 2012. Genetics: Analysis and Principles 4th Ed. New York: McGraw-Hill. pp 868.
Muller-Hill, Benno, 1996. The lac Operon, a Short History of a Genetic Paradigm. Berlin: Walter de
Gruyter. pp. 7–10 .
Marbach, A., Bettenbrock, K., 2012. Lac operon induction in Escherichia coli: Systematic
comparison of IPTG and TMG induction and influence of the transacetylase LacA. Journal of
Biotechnology. 157: 82–88.
References