how the enzymes are regulated and biosynthesised in microorganisms

1. Biosynthesis and
regulation of enzyme
in microorganisms
PRESENTED BY: SWATI RAINA
IBT SEM 1ST
ROLL NO: 10

2. Bacteria have developed sophisticated mechanisms for the
regulation of both catabolic and anabolic pathways
 Vibrio cholerae does not produce the cholera toxin that causes
diarrhoea unless it is in the human intestinal tract. & Bacillus subtilis
does not produce enzymes for tryptophan until it find pre-existing
tryptophan in the medium.
 Bacteria do not synthesize degradative(catabolic) enzymes unless the
substrate for these enzymes are present in their environment.
 Similarly for anabolic Bacterial cells shut down biosynthetic
pathways when the end product of the pathway is not
needed or is readily obtained by uptake from the environment.

3. TYPES OF ENZYMES
 CONSTITUTIVE ENZYME : produced independently of
the composition of the medium.
 INDUCIBLE ENZYME : produced when they are needed,
only in the presence of substrate.
 REPRESSIBLE ENZYME : this is downregulated (turned
off) when there is the formation of the end product.

4. Regulation
Of
Enzyme
synthesis
End product repression
Enzyme induction
Enzyme
activity Feedback inhibition/
end product
Catabolite repression
Negative
control :
because it dec
rate of
transcription
positive
control :
because it inc
rate of
transcription

5. POINTS OF REGULATION
 There are some regulatory processes & there are some points of
regulation at the level of transcription (enzyme induction &
repression) which are regulated by different properties of enzyme.
 Some examples are:
Allosteric protein
Enzyme repression
Enzyme induction
Catabolite repression

6. Allosteric Protein
 An allosteric protein is one which has an active (catalytic) site an
d an allosteric (effector) site.

7. Feedback Inhibition
 Feedback inhibition (or end pro
duct inhibition) is a mech
anism for the inhibition of
performed enzymes.
 The final product is able to feed bac
k to the first step in the pathway an
d to regulate its own biosynthesis.

8. Enzyme Repression
This prevents the synthesis of the enzyme concerned with
the synthesis of the particular end product.
 Similar to feedback
Inhibition but spends
less energy than it.

9. The product of trpL gene is a trp
repressor, an allosteric protein
which is regulated by tryptophan.
In absence of tryptophan this
repressor is made in inactive form in
small amounts, thus transcription
occurs and tryptophan is produced.
In presence of tryptophan, trp acts
as a corepressor and binds to the
inactive repressor making it active
thus repressor binds to DNA and
blocks transcription
Hence tryptophan is not produced.

10. Enzyme induction
 Metabolites or substrates, in some cases
can turn on inactive genes so that they are transcribed.
 The substrate/compound structurally similar to the substrate, evoke
s the formation ofenzyme(s) which are usually involved in the degrada
tion of the substrate.
 Enzymes that are synthesized as a result of genes being turned on are cal
led inducible enzymes and
the substance that activates gene transcription is called the inducer.
 The enzyme is only produced when it’s substrate is present thus energy
is saved. E.g lactose degradation in E. coli

11. • Only in the presence of la
ctose does the
bacterium synthesize the e
nzymes that are necessary
to utilize lactose.
• In the presence of lactose,
the Repressor cannot bind
to the
operator region, so that th
e genes for lactose transpo
rt and cleavage are
transcribed.
• In the absence of
lactose, the Repressor is ac
tive and will bind to
operator with the result t
hat the genes for lactose
metabolism are not tran
scribed.

12. Catabolic repression
 Catabolite repression is a type of positive control of
transcription, since a regulatory
protein affects an increase (upregulation) in the
rate of transcription of an operon.
 Example of catabolic repression is the diauxic growth of E.Coli in the
presence of glucose & lactose.
 Glucose is utilised before lactose because lactose degradation require
2 enzymes.
 Thus the glucose represses the enzymes for lactose utilisation this is
known as catabolic repression.

13. IN PRESENCE OF GLUCOSE
 Adenylate cyclase (AC)
Blocked
 AC is required to synthesise cAMP
 When cAMP level is low or absent
 cAMP can’t bind to CAP
 Transcription does not occur
IN ABSENCE OF GLUCOSE
 Adenylate cyclase (AC) is active
 cAMP is synthesised & level is high
CAP is activated
 Transcription occurs ( In presence of inducer i.e
lactose)