Enzymes are proteins that act as biological catalysts to speed up biochemical reactions. They are classified based on the type of reaction they catalyze and have a complex three-dimensional globular structure. Enzymes specifically bind to substrates through their active sites to lower the activation energy of reactions, speeding up the formation of products. The mechanism of enzyme action was originally proposed to be lock-and-key binding, but is now understood to involve induced fit, where the enzyme and substrate mutually adjust their shapes for catalysis. Enzymes can be regulated by various factors like substrate concentration, temperature, pH, inhibitors, and activators.

1. ENZYMES
CourseTitle: Basic
Pharmaceuticals
Course Code: ACCE 262
Applied Chemistry & Chemical
Engineering

2. SHAIKH ASHRAFUL ALAM

3. ENZYMES
A substance
produced by a living
organism which acts
as a catalyst to bring
about a specific
biochemical reaction.

4. Classification of Enzymes
Oxidoreductases
Transferases
 Hydrolases
Lyases
Isomerases
Ligases

5. Enzyme structure
 Enzymes are
proteins
 They have a
globular shape
 A complex 3-D
structure

6. Part of Enzyme
Enzyme
Pyruvate Dehydrogenase(active form) Inactive form(apo enzyme)
Prosthetic group
Cofactor
(Inorganic or Metal ion)
Co-enzyme
(Organic ion)

7. Properties of Enzymes
Most enzymes are proteins
They are all biological catalyst
A small amount of enzyme can effect the change of a large amount of
chemical.
Enzymes work is affected by temperature, pH and pressure.
They can be destroyed by excessive heat.
The reaction are reversible.

8. 8
Enzymes
Free
Energy
Progress of the reaction
Reactants
Products
Free energy of activation
Without Enzyme
With Enzyme

9. Factors Affecting Enzymes
Substrate concentration
pH
Temperature
Inhibitors

10. Mechanism of enzyme action
Lock and key theory
Induced fit mechanism

11. LOCK AND KEY MODEL
The lock and key model of enzyme action, proposed earlier this
century, proposed that the substrate was simply drawn into a closely
matching cleft on the enzyme molecule.
Substrate
Enzyme
Products
Symbolic representation of the lock and key model of enzyme action.
1. A substrate is drawn into the active sites of the enzyme.
2. The substrate shape must be compatible with the enzymes active site in
order to fit and be reacted upon.
3. The enzyme modifies the substrate. In this instance the substrate is
broken down, releasing two products.

12. INDUCED FIT MODEL
More recent studies have
revealed that the process is
much more likely to involve
an induced fit.
The enzyme or the reactants
(substrate) change their shape
slightly.
The reactants become bound to
enzymes by weak chemical
bonds.
This binding can weaken bonds
within the reactants themselves,
allowing the reaction to proceed
more readily.
The enzyme
changes shape,
forcing the substrate
molecules to
combine.
Two substrate
molecules are
drawn into the cleft
of the enzyme.
The resulting end
product is released
by the enzyme
which returns to its
normal shape, ready
to undergo more
reactions.

13. Induced Fit
• A change in the
shape of an enzyme’s
active site
• Induced by the
substrate

14. Induced Fit
• A change in the configuration of an
enzyme’s active site (H+ and ionic
bonds are involved).
• Induced by the substrate.
Enzyme
Active Site
substrate
induced fit

15. Inhibitors
Inhibitors are chemicals that reduce the rate of
enzymic reactions.
The are usually specific and they work at low
concentrations.
They block the enzyme but they do not usually
destroy it.
Many drugs and poisons are inhibitors of enzymes in
the nervous system.

16. Two examples of Enzyme
Inhibitors
a. Competitive inhibitors: are
chemicals that resemble an
enzyme’s normal substrate and
compete with it for the active
site.
Enzyme
Competitive inhibitor
Substrate

17. Inhibitors
b. Noncompetitive inhibitors:
Inhibitors that do not enter the
active site, but bind to another part
of the enzyme causing the enzyme to
change its shape, which in turn
alters the active site.
Enzyme
active site
altered
Noncompetitive
Inhibitor
Substrate

18. Use of Enzyme activators
Enzyme activators are molecules that bind
to enzymes and increase their activity.
 They are the opposite of enzyme
inhibitors.
These molecules are often involved in the
allosteric regulation of enzymes in the
control of metabolism.

19. Specificity of Enzyme
• Stereospecificity
CH2COOH H-C-COOH
CH2COOH HOOC-C-H
Succinic acid Fumaric acid

20. Specificity of Enzyme (reaction specificity)
COOH COOH CH
CH2 CH CO
C.OH.COOH CO2 COOH
CH2 COOH
COOH
(+ CH3COOH) Decarboxylation
Citric acid
Pyruvic acid

21. Specificity of Enzyme (reaction specificity)
Oxaloacetic acid
COOH COOH
CH2 CH2
CHOH CHNH2
COOH COOH
Malic acid Aspartic acid
Enzymatic reactions of oxaloacetic acid

22. Specificity of Enzyme (substrate specificity)
NH2CONH2 2NH3 + CO2
H2O
Urease

23. Summary: Enzymes
• Enzymes work very rapidly and help to speed up biological
reactions.
• Enzymes can be used multiple times (however they do degrade
eventually).
• Enzymes can work in both directions of a chemical reaction.
• Enzymes have optimal temperatures and pH that they will
operate. Beyond these optimum ranges they will either not work
or become denatured (unfolded/breakdown).
• Enzymes are usually specific to one particular substrate.