Regulation of Gene Expression Regulation of Gene Expression

By – Ajay Kumar M.Sc. -2Paper- 1

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

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:

PromoterRepressorOperator (controlling site)Coding sequences

Structure of Lac Operon

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.

-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

Repression

E. Coli lac operon:

• Lactose = disaccharide (glucose + galactose), provides energy.

Derepression

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.

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/

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