2. DEFINITION
Gene expression refers to the multistep process that
ultimately results in the production of a functional
gene product, either ribonucleic acid (RNA) or protein
Regulated genes are expressed only under certain
conditions
It is the basis for cellular differentiation,
morphogenesis, and adaptability of any organism
3. LEVEL OF GENE REGULATION
Prokaryotes: Transcription
Eukaryotes : Transciption and post transcriptional
and post-translational processes
5. REGULATORY SEQUENCES AND
MOLECULES
Regulation of transcription is controlled by regulatory
sequences of DNA
Embedded in the noncoding regions of the genome.
The interaction between these DNA segments and
regulatory molecules (transcription factors) can
engage or repress the transcriptional machinery
6. TYPES OF TRANSCRIPTION FACTORS
a) Cis acting elements:
Regulatory sequences flanking a gene
Influence gene expression only on the same
chromosome
b) A trans-acting factor
Proteins which transit through the cell from its site
of synthesis to its DNA-binding site
8. REGULATION OF PROKARYOTIC GENE
EXPRESSION
Primarily at the level of transcription
By the binding of trans-acting proteins to cis-acting
regulatory elements on their single DNA molecule
Affects the initiation or premature termination of
transcription
9. OPERON
The structural genes that code for proteins involved in
a particular metabolic pathway are often found
sequentially grouped together along with the cis-
acting regulatory elements
The genes are, thus, coordinately turned on or off as a
unit.
This entire package is called as operon
Eg, Lactose operon, tryptophan operon
10. Role of operators in prokaryotic
transcription
OPERATOR: A segment of DNA that regulates the
activity of the structural genes of the operon
REPRESSOR: As long as the repressor is bound to the
operator, no proteins are made.
INDUCER: binds to the repressor, causing the
repressor to change shape so that it no longer binds
the operator.
13. LACTOSE OPERON
It contains the genes that code for three proteins
involved in the catabolism of the disaccharide lactose
1. lacZ gene: β-galactosidase
2. lacY gene : permease
3. lacA gene : transacetylase
14. THE REGULATORY COMPONENTS
The regulatory portion has 3 sites:
1. Promoter : Binds RNA polymerase
2. Operator (O) site : Binds repressor encoded by lac-l
gene
3. CAP site: Binds cAMP & CAP (Catabolite Activator
Protein)
15. Regulatory Sites & Their Binding Factors
Lac-l CAP Site Promoter Operator Gene
RepressorRNA Poly.
C AMP +
CAP
16. PRE-REQUISITES FOR GENE EXPRESSION
The lacZ, lacY, and lacA genes are expressed only when:
The O site is empty
The CAP site is bound
Lac-l CAP site Promoter Operator Genes
RNA
Poly.
C AMP
+CAP
22. III.BOTH LACTOSE AND GLUCOSE
ALTHOUGH
Repressor not bound to the operator region
BUT
Glucose inactive adenyl cyclase no cAMP CAP
remains unbound CAP site remains empty
promoter cannot initiate transcription
OPERON REPRESSED
24. Regulation at the level of ribosomes
I.Stringent response in Ecoli:
Regulation in response to amino acid starvation is
known as the stringent response.
The binding of an uncharged transfer RNA (tRNA) to the
A site of a ribosome
Triggers a series of events that leads to the production of
a polyphosphorylated guanosine, ppGpp.
Catalyzed by stringent factor (RelA)
Elevated levels of ppGpp result in inhibition of rRNA
synthesis
26. II.Regulatory ribosomal proteins
Operons for ribosomal proteins (r-proteins)
Can be inhibited by an excess of their own protein
products
For each operon, one specific r-protein functions in
the repression of translation
It binds Shine-Dalgarno (SD) sequence and inhibits
binding of the small ribosomal subunit to the SD
sequence.
Also binds to rRNA and with a higher affinity than for
mRNA again inhibiting translation
If the concentration of rRNA falls, the r-protein then
is available to bind its own mRNA and inhibit its
translation.