Regulation of gene expression LAC OPERON.pptx

1. Dr. Rama Kant Upadhyay

2. REGULATION OF GENE EXPRESSION
In eukaryotes, the regulation could be exerted at
• Transcriptional level (formation of primary transcript)
• Processing level (regulation of splicing)
• Transport of mRNA from the nucleus to the cytoplasm
• Translational level
In prokaryotes, gene expression is regulated at the transcriptional level when
proteins bind to operons to activate or repress transcription.

3. Operons occur in prokaryotes, but not eukaryotes
In eukaryotes, each gene is made on individual mRNAs and each gene has its own
promoter.
Operons are prokaryotic arrangements of multiple genes (with common functions)
under the control of a SINGLE PROMOTER.
The term “operon” was coined by Jacob and Monod
LAC OPERON
Proposed by Jacob and Monad
In E.coli (Escherichia coli)
For metabolism of lactose (Lac)
1- Inducible/ Positive operon – when lactose present
2- repressible/ negative operon - when lactose absent

4. OPERON
an operon is a functioning unit of DNA containing a cluster of genes under the
control of a single promoter
TYPES OF OPERON
1- Inducible
2- repressible
REGULATOR
GENE
( I )
PROMOTER
GENE
(p )
OPERATOR
GENE
(o )
STRUCTURAL
GENES

5. • Regulator (i) – synthesize repressor protein
• Promoter (p) – binding site of enzyme RNA Polymerase
• Operator (o) – binding site for repressor protein
• Structural gene- (z, y, a)
Genes in Lac Operon
y
Z – beta galactosidase : breakdown lactose into galactose and glucose
Y- permease – transports lactose into cell
A- transacetylase- acylation of galactose
Only lacZ and lacY appear to be necessary for lactose catabolism

6. Regulator gene (i)
• In the absence of lactose
• synthesize repressor protein which binds on operator (o) and blocks the
movement of RNA polymerase enzyme results in no transcription

7. Promoter (p)
• Binding site for RNA Polymerase enzyme
• RNA Pol. Synthesize different types of RNA during the transcription process.
• Polymerase transcribes the structural genes (z, y, a)

8. Operator (o)
• In the absence of lactose
• Regulator gene (i) synthesizes repressor protein which binds on operator (o.
• Repressor blocks the movement of RNA polymerase enzyme results in no
transcription

9. • Lactose
• Allolactose
Inducer
The inducer molecule does not allow the binding of repressor proteins
on the operator.
Help in the process of transcription

10. THANK YOU!
Source: NCERT Text book, Google images