The document summarizes regulation of gene expression through the lac operon in E. coli. It describes how Francois Jacob and Jacques Monod discovered the lac operon in the 1960s and were awarded the Nobel Prize. The lac operon is a cluster of genes whose expression is regulated by an operator and repressor protein. In the absence of lactose, the repressor binds the operator to prevent transcription. When lactose is present, it binds to the repressor and causes derepression, allowing transcription of genes encoding beta-galactosidase, lactose permease, and transacetylase which break down lactose. Positive control involves cAMP and CAP activating transcription when glucose levels are low.

1. Regulation of Gene ExpressionRegulation of Gene Expression
By – Ajay Kumar
M.Sc. -2
Paper- 1

2. Discovery
Francois Jacob and Jacques
Monod (Pasteur Institute,
Paris, France)
• Studied the organization and
control of the lac operon in
E. coli.
• Awarded the Nobel Prize in
Physiology and Medicine
1965.
Francois Jacob
Jacques Monod

3. What is Operon ???
Cluster of genes in which expression is regulated by operator-
repressor protein interactions. plus the operator region itself and
the promoter.
• Contents of an operon:
Promoter
Repressor
Operator (controlling site)
Coding sequences

4. Structure of Lac Operon

5. Regulated genes
Control cell growth and cell division.
Expression is regulated by the needs of the cell and or
organism.
Constitutive genes
Continuously expressed.
House keeping genes such as those required for protein
synthesis and glucose metabolism.

6. -galactosidase (lacZ)
•Breaks lactose into glucose + galactose.
•Converts lactose to the allolactose, regulates lac operon.
•Lactose permease (lacY)
•Transports lactose across cytoplasmic membrane.
•Transacetylase (lacA)
•transfers an acetyl group from acetyl-CoA to -galactosides.
Structural gene

7. Repression

8. E. Coli lac operon:
• Lactose = disaccharide (glucose + galactose), provides energy.

9. Derepression

10. Positive control in the lac operon:
• When glucose and lactose are present, E. coli preferentially uses glucose due to
low levels of active CAP (low cAMP).
• Catabolite activator protein (CAP) binds cAMP, activates, and binds to a CAP
recognition site upstream of the promoter (cAMP is greatly reduced in presence
of glucose).
• CAP changes the conformation of DNA and facilitates binding of RNA
polymerase and transcription.
• Adding cAMP to cells restore transcription of the lac operon even when glucose
is still present.

12. Bibliography & webliography
I-Genetics A Molecular approach third edition
By- Peter J. Russell
Genetics (from Genes to Genomes)
By- Michael Goldberg,Leory Hood
www.cat.cc.md.us/courses/bio141/lecguide/
unit4/genetics/protsyn/regulation/

13. THANK YOU