The trp operon in E. coli bacteria encodes genes for the biosynthesis of the amino acid tryptophan. It is regulated by the trp repressor protein - when tryptophan levels are low, the repressor does not bind to the operator, allowing transcription of the operon; when tryptophan levels are high, it binds to the operator and blocks transcription, turning the operon off. This allows the bacteria to efficiently control tryptophan production depending on environmental availability.

3. Introduction
 The trp operon is an operon a group of genes that is
used,or transcribed that codes for the components for
production of tryptophan. The trp operon is present in
many bacteria but was first characterized in E.coli.
 Trp operon discovered in 1953 by Jacques Monod and
colleagues,the trp operon in E.coli was the first repressible
operon to be discovered.
 Tryptophan is an aromatic amino acid, and is required for
synthesis of all protein that contain tryptophan. If
tryptophan is not present in the medium in adequat
quantity, the bacterial cell has to make it, as it is required
for the growth of the bacteria.

4. • The tryptophan operon, found in E.coli bacteria, it is a
group of genes that encode biosynthetic enzymes for the
amino acid tryptophan.
• The tryptophan operon is expressed (turned on) when
trptophan levels are low and repressed (turned off) when
they are high.
• The trp operon is regulated by the trp repressor. When
bound to tryptophan, the trp repressor blocks expression
of the operon.
• Tryptophan biosynthesis is also regulated by attenuation (a
mechanism based on coupling of transcription and
translation).

5. • Bacteria such as E.coli (friendly inhibitant of our gut) need
amino acid to survive because,like us they need to build
protein. One of the amino acids they need is tryptophan. If
tryptophan is available in the environment, E.coli will take
it up and use it to build proteins. However, E.coli can also
make their own trptophan using enzymes that are encoded
by five gene.These five genes are located next to each other
in what is called trp operon.
• If the tryptophan is present in the environment, then
E.coli bacteria don’t need to synthesize it, so transcription
of the gene in the trp operon is switched off. When
tryptophan availability is low, the operon is switched on
the gene are transcribed, biosynthetic enzymes are made
and more tryptophan is produced
WHAT IS THE TRP OPERON?

6. STRUCTURE OF TRP OPERON

8. TURNING OPERON “ON” AND “OFF”
 What does the operator do?
This stretch of DNA is recognized by a regulatory protein known
as the trp repressor. When the repressor binds to the DNA of the
operator, it keeps the operon from being transcribed by
physically getting in the way of RNA polymerase the
transcription enzyme.
• WHERE DOES THE TRP REPRESSOR COME FROM?
The trp repressor does not always binds to DNA. Instead, it bind
and blocks transcription only when tryptophan is present. When
tryptophan is around, it attaches to the repressor molecule an
changes their shape so they become active. A small molecule like
tryptophan which switches a repressor into its active state called
as corepressor.

9.  A cluster of functionally related genes that can be
under coordinated control by a single on-off switch.
 The regulatory switch is a segment of DNA called an
operator usually usually positioned within the
promoter.
 An operon is the entire stretch of DNA that includes
the operator, the promoter, and the genes that they
control.
 The operon can be switched off by a protein repressor.
 The repressor prevents gene transcription by binding
to operator and blocking RNA polymerase.

10.  The repressor is the product of a separate regulatory gene
 The repressor can be active or inactive form,depending on
the presence of other molecule.
 A corepressor is a molecule that cooperates with a repressor
protein to witch an operon off.
 The trp operon of E.coli contains five structural gene(trpE,
trpD, trpC ,trpB, trpA)and the regulatory elements-primary
promoter(trpP),operator(trpO),attenuator(trpa),secondary
internal promoter(trpP2),and terminator(trpt)
 The five structural genes of trp operon codes for three
enzymes(two enzymes contain two different
subunits)required for the synthesis of tryptophan from
chorismate.

11. When there is little tryptophan in the cell, the repressor is
inactive(because no tryptophan is available to bind and
activate it). It does not attach to the DNA or block
transcription, and this allows the trp operon to be
transcribed by RNA polymerase

12.  In this system, the trp repressor acts as both a sensor
and a switch. It senses whether tryptophan is already
present at high level, and if so, it switches the operon
to the off position,preventing unnecessary
biosynthetic enzymes from being made.

13. Comparison of lac and trp operon
 IN the lac operon, allolactose binds to the repressor
protein,allowing gene transcription,while in trp
operon,tryptophan binds to the repressor protein
effectively blocking gene transcription.
 The trp operon produces products that are used to
manufacture an amino acid, tryptophan. The pathway
controlled by the trp operon in an example of an anabolic
pathway.
 The lac operon control a catabolic pathway. one that breaks
down complex molecules to release energy for biologycal
work.
 Lac operon is inducible gene regulation and trp
operon is repressible gene regulaion.