1. Menon Lakshmi Suresh
1st MSC BPS

2. OBJECTIVES:
• Define enzyme, substrate, active site
• Explain enzyme substrate specificity (Lock and Key
Model, Induced-Fit Model)
• Describe the effects of temperature, pH, and substrate
concentration on enzyme activity
• Define co-enzymes and co-factors, give examples and
describe their role in enzymatic activity.
• Uses of Enzymes

3. • Enzymes are organic catalysts
• All enzymes are composed of
Proteins (tertiary and
quaternary structures)
• Because enzymes are
composed of proteins, their
shape is important to their
function.
(If you change the shape of
the protein that composes
the enzyme you alter or
destroy the enzyme.)

4. • Enzymes are specific to which molecules they act
upon. The substances they act upon are called
substrates.
• Most enzymes end with the suffix –ase.
Sucrase, Lactase, Maltase
• For example the enzyme found in saliva which
begins the chemical hydrolysis of amylose is
called amylase.
• Enzymes are not used up or destroyed in the
reaction process and at the end of their reaction
will bind with more substrate molecules and
repeat the same chemical process. Therefore,
small numbers of these molecules can have a
great effect.

5. • Each enzyme is the specific helper to
a specific reaction
– each enzyme needs to be the right shape
for the job
– enzymes are named for the reaction
they help
• sucrase breaks down sucrose
• proteases breakdown proteins
• lipases breakdown lipids
• DNA polymerase builds DNA

6. • Enzymes affect the
rates of reactions by
lowering the amount of
energy of activation
required for the
reactions to begin.
Therefore processes
can occur in living
systems at lower
temperatures or energy
levels than it would
require for these same
reactions to occur
without the enzymes
present.

7. • Enzymes work by weakening bonds
which lowers activation energy

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

9. Enzymes aren’t used up
• Enzymes are not changed by the reaction
– used only temporarily
– re-used again for the same reaction with other
molecules
– very little enzyme needed to help in many
reactions
enzyme
substrate product
active site

10. • The substance (reactant) an enzyme
acts on is the substrate
Enzyme
Substrate Joins

11. • A restricted region of an enzyme
molecule which binds to the substrate.
EnzymeSubstrate
Active
Site

12. How Enzymes Bind to Substrates
• There are two proposed methods by
which enzymes bind to their substrate
molecules:
a. Lock and Key Model
b. Induced-Fit Model

13. Enzymes
• Lock and Key Analogy: lock = enzyme, key =
substrate.

14. It’s shape that matters!
• Lock & Key model
– shape of protein
allows enzyme &
substrate to fit
– specific enzyme for
each specific
reaction

15. 1
2
3

16. Induced-Fit Model
The induced model states that the substrate binds to the active
site and induces or causes a change in shape of the active site
so that it is a complimentary fit. This model explains why
some enzymes can act on more than one substrate.
S1
S2
S3 P1 P1SUBSTRATE
MOLECULES
ENZYME SUBSTRATE
COMPLEX
Products
Active site in inactive state
Substrate induces a
change in active site
so that it is complimentary
The active site of the enzyme returns to the inactive state after
the products are released and now can react with more substrate.
ENZYME
S1

17. Induced Fit

18. 18
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

19. 19
What Affects Enzyme Activity?
• Three factors:
1. Environmental Conditions
2. Cofactors and Coenzymes
3. Enzyme Inhibitors

20. 1. Environmental Conditions
1. Extreme Temperature are the most
dangerous
- high temps may denature (unfold)
the enzyme.
2.pH (most like 6 - 8 pH near
neutral)
3.Ionic concentration (salt ions)

21. Environmental Factors Which Affect
Enzyme Activity: Temperature
All enzymes have an optimum
temperature at which they
work best. If you observe
the enzyme’s activity below
the specific temperature it
will steadily increase until it
reaches the optimum. After
the optimum temperature
is reached the enzymes
activity drops dramatically
due to denaturing.
Depending on the species, the
range of optimum activity is very
broad. Above is a comparison of
human enzyme activity with that of
bacteria found in hot springs and
oceanic vents.

22. Environmental Factors Which
Affect Enzyme Activity: pH
All enzymes have an optimum pH at
which they work best. If the pH falls
below or rises above the optimum
value, enzymatic activity decreases
as a result of denaturing.
In the human body’s digestive tract
there are variations in pH from area
to area. The stomach’s juices’ pH
is around 2 (acidic), the enzyme pepsin
found in the gastric juices has
optimum activity at a pH of 2. The small
intestine’s juice’s pH is around 8 (basic).
The enzyme trypsin found in the small
intestine’s juices has optimum activity at
a pH of 8.

23. Environmental Factors Which Affect
Enzyme Activity: Substrate Concentration
The concentration of substrate also has an affect on the rate of enzyme
activity. If the concentration of substrate is increased while the
concentration of enzyme is constant, the level of enzyme activity will
increase until a point of saturation is reached. At this point there are no
enzymes available to react with excess substrate and the rate of the
reaction stabilizes. No matter if you continue to add substrate, the
reaction rate will not increase!
Increasing Substrate Concentration
Rate of Reaction
Point of Saturation, all active
sites are filled with substrate.

24. 2. Cofactors and Coenzymes
• Some enzymes require another organic molecule or
substance to be present before they can function.
• These organic molecules or substances are called Co-
enzymes or Co-factors.
• Co-enzymes are organic molecules (usually
vitamins)
• Co-factors are inorganic substance (minerals).
This is one of the reasons it is so important to eat a well
balanced diet.

25. • For example, Vitamin K is necessary for the
enzyme responsible for blood clot formation.
A lack of vitamin K leads to easy bruising and
prolonged bleeding when injuries occur.
• Calcium is a co-factor which is required by
several enzymes for their activation.

26. 3. Enzymatic inhibition.
To regulate enzyme activity, there must be
some form of prevention of binding of
substrate with active site. There are two
forms of inhibition:
1. Competitive inhibition
2. Noncompetitive inhibition

27. 27
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

28. 28
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

29.  ENZYMES IN INDUSTRY
 ENZYMES IN CLOTHES/DISHWASHER
DETERGENTS
 ENZYMES IN SLIMMING AIDS
 ENZYMES IN BABY FOOD
 STARCH(HFCS)
 ENZYMES TO DIAGNOSE AND
CONTROL DISEASE
 ENZYMES TO DIAGNOSE DISEASE