micribiology

1. Presented to Sir Abdul Majid
Presented by Qasim Ali, Kashif Sohail
BS 7th Zoology
Regulation of Enzymatic Activity and Metabolic Pathways
Department of Zoology
Kohat university science & technology ,Kohat
Pakistan

2. The Sensitivity of Enzymes to Their Environment
• The activity of an enzyme is highly influenced by the cell’s environment.
• Operate only
under the natural temperature, pH, and osmotic pressure of an
organism’s habitat.
• changes in normal conditions tend to be chemically unstable
• Low temperatures inhibit catalysis
• High temperatures denature the apoenzyme.
• Denaturation
is a process by which the weak bonds that collectively maintain the
native shape of the apoenzyme are broken.

3. • Due to it
causes extreme distortion of the enzyme’s shape
prevents the substrate from attaching to the active site
block metabolic reactions
can lead to cell death.
• Low or high pH or certain chemicals (heavy metals, alcohol) are also
denaturing agents.
 Regulation of Enzymatic Activity
• Metabolic reactions proceed in a systematic, highly regulated manner
that maximizes the use of available nutrients and energy.
• The cell responds to environmental conditions by adopting those
metabolic reactions that most favor growth and survival.

4. • Because enzymes are critical to these reactions, the regulation of
metabolism is largely the regulation of enzymes by an elaborate
system of checks and balances.
 Metabolic Pathways
• Metabolic reactions rarely consist of a single action or step.
• More often, they occur in a multistep series or pathway, with each
step catalyzed by an enzyme.
• An individual reaction is shown in various ways, depending on the
purpose.
• The product of one reaction is the reactant (substrate) for
the next,

5. Forming a linear chain of reactions
Many pathways have branches

6. Others take a cyclic form

7. • Every pathway has one or more enzyme pacemakers that
sets the rate of a pathway’s progression.
• These enzymes respond to various control signals and, in so doing,
determine whether a pathway proceeds.
• Regulation of pacemaker enzymes proceeds on two fundamental
levels.
 Either the enzyme itself is directly inhibited or activated,
or the amount of the enzyme in the system is altered (decreased or
increased).
• Factors that affect the enzyme directly provide a means for the
system to be finely controlled or tuned, whereas regulation at the
genetic level (enzyme synthesis) provides a slower, less sensitive
control.

8. Direct Controls on the Action of Enzymes
• The bacterial cell has many ways of directly influencing the
activity of its enzymes.
•It can inhibit enzyme activity by supplying a molecule that
resembles the enzyme’s normal substrate.
• The “mimic” can then occupy the enzyme’s active site,
preventing the actual substrate from binding there.

9. •Since the mimic cannot actually be acted on by the enzyme,
or function in the way the product would have, the enzyme is
effectively shut down.
Competitive inhibition
•This form of inhibition is called competitive inhibition, since
the mimic is competing with the substrate for the binding
site.(In chapter 12 you will see that some antibiotics use the
same strategy of competing with enzymatic active sites to
shut down metabolic processes.

10. Enzyme
EnzymeEnzyme
Competitive Inhibition
Non competitive Inhibition
Normal
substrate
Competitive
inhibitor with
similar shape
Both molecules
compete for
the active site.
Reaction is blocked
because competitive
inhibitor is incapable
of becoming a
product
Reaction proceeds
Substrate
Active site
Regulatory site
Reaction proceeds
Product
Regulatory
molecule
(product)
Reaction is blocked because
binding of regulatory molecule
in regulatory site changes
conformation of active site so
that substrate cannot enter.

11. •Another form of inhibition can occur with special types of
enzymes that have two binding sites—the active site and
another area called the regulatory site.
•These enzymes are regulated by the binding of molecules other
than the substrate in their regulatory sites. Often the
regulatory molecule is the product of the enzymatic reaction
itself.
•This provides a negative feedback mechanism that can slow
down enzymatic activity once a certain concentration of
product is produced. This is noncompetitive inhibition, since
the regulator molecule does not bind in the same site as the
substrate.

12. Controls on Enzyme Synthesis
•Controlling enzymes by controlling their synthesis is another
effective mechanism, because enzymes do not last indefinitely.
Some wear out, some are deliberately degraded, and others
are diluted with each cell division. For catalysis to continue,
enzymes eventually must be replaced. This cycle works into
the scheme of the cell, where replacement of enzymes can be
regulated according to cell demand. The mechanisms of this
system are genetic in nature; that is, they require regulation of
DNA and the protein synthesis machinery.

14. Cont…..
•Enzyme repression is a means to stop further synthesis of an
enzyme somewhere along its pathway. As the level of the end
product from a given enzymatic reaction has built to excess,
the genetic apparatus responsible for replacing these
enzymes is automatically suppressed .The response time is
longer than for feedback inhibition, but its effects are more
enduring.
•A response that resembles the inverse of enzyme repression
is enzyme induction. In this process, enzymes appear (are
induced) only when suitable substrates are present—that is,
the synthesis of enzyme is induced by its substrate. Both
mechanisms are important genetic control systems in
bacteria.

15. •A classic model of enzyme induction occurs in the response of
Escherichia coli to certain sugars. For example, if a particular
strain of E.coli is inoculated into a medium whose principal
carbon source is lactose, it will produce the enzyme lactase to
hydrolyze it into glucose and galactose. If the bacterium is
subsequently inoculated into a medium containing only sucrose
as a carbon source, it will cease synthesizing lactase and begin
synthesizing sucrase. This response enables the organism to
adapt to a variety of nutrients, and it also prevents a microbe
from wasting energy, making enzymes for which no substrates
are present.

16. THANK YOU