Enzymes have several key characteristics: 1) They speed up chemical reactions by lowering the activation energy needed. 2) They are required in minute amounts and remain unchanged after reactions. 3) They are highly specific, with each enzyme having a unique three-dimensional structure that only binds complementary substrates. Their activity is also affected by temperature and pH - they have optimal temperatures and pH levels at which they are most active, and are deactivated outside these ranges. Some enzymes also require co-factors to function or can catalyze reversible reactions.

1. Topic 4: Chapter 5
EnzymesEnzymes –– Part 2Part 2
Characteristics
Characteristics
of Enzymes
of Enzymes

2. Characteristics of Enzymes?
Enzymes
1)speed up chemical reactions
2)are required in minute amounts
3)are highly specific in their action
4)are affected by temperature
5)are affected by pH
6)Some catalyse reversible reactions
7)Some require co-enzymes
8)Are inhibited by inhibitors

3. (1) Enzymes Speed up chemical reactions(1) Enzymes Speed up chemical reactions
Activation Energy
with enzyme
Activation
Energy without
enzyme
Substrate
Products:
Energy
Time
• By lowering the activation energy needed to
start the reaction.

4. (2) Enzymes are required in minute amounts(2) Enzymes are required in minute amounts
Sucrose Glucose + Fructose
• They remain chemically unchanged after
catalysing the reactions.
• The same enzyme molecules can be reused
over again.
• Therefore, only a small amount of enzyme is
required to catalyse a large number of reactions
Sucrase
Chemically unchangedChemically unchanged

5. Maltose Glucose + GlucoseMaltose Glucose + Glucose
(3) Enzymes are highly specific(3) Enzymes are highly specific
• Each chemical reaction is catalysed by its own
specific, unique enzyme.
• This is due to every enzyme’s specific 3-d
configuration.
• How the shape of an enzyme affects its function can
be explained by the “LOCK & KEY HYPOTHESIS”.
Maltase
Starch Maltose
Amylase

6. • Enzymes are proteins and each has an active site.
• Active sites are depressions on the surface of
enzyme molecules with specific shape and
specific charges.
• Active sites are formed due to the way the proteins
are folded and held together by H-bonds.
Lock &
Key
Hypothesis
Lock &
Key
Hypothesis

7. • Every active site has it’s own specific shape and
charges.
• It only allows substrates with a
COMPLEMENTARY shape and charge to bind
with it to form an Enzyme-Substrate Complex
Lock &
Key
Hypothesis
Lock &
Key
Hypothesis
Active
Sites
Substrate Enzyme-Substrate Complex Products + EnzymeSubstrate Enzyme-Substrate Complex Products + Enzyme
Enzyme

8. Anabolic Reaction - Synthesis
Catabolic Reaction - Hydrolysis

9. TheThe
LockLock
andand KeyKey
HypothesisHypothesis
• The substrate binds to a free enzyme with a
complementary active site to form the enzyme-
substrate complex
• The enzyme-substrate complex brings about the
necessary reactions
• The product separates from the enzyme, leaving
the enzyme molecule unchanged and free to
combine again with more substrate molecules

10. (4) Enzymes are affected by temperature(4) Enzymes are affected by temperature
• Enzymes can function
over a range of
temperatures.
• But all enzymes have
their own optimum
temperature.

11. Optimum temperature
• The optimum temperature is the temperature at
which the enzyme is most active, catalysing the
largest number of reactions per second.
• Different enzymes have different optimum temp.
• Example:
most enzymes in the human body
functions best at about 37-40o
C, near
body temperature.
Enzymes of thermophilic bacteria that
live in hotsprings will have very high
optimum temperatures.

12. How enzyme activity is affected by temperature
• At low temperature, enzymes are INACTIVE.
• As temperature rises, the rate of enzyme activity
increases (usually 2x as active for every 10o
C
rise).
• Enzyme reaching maximum rate of activity at OT
NOTE:
Describe the
enzyme activity with
respect to the Rate-
Temperature Graph
• Raising the temperature increases the
kinetic energy supplied to the substrate
and enzyme molecules.
• This increases the no. of collisions
between enzyme and substrate molecules.
• Increasing the rate of formation of enzyme-
substrate complex.
• Rate of formation of the products increases
up till the optimum temperature
Increasing temp up to optimum temp.

13. How enzyme activity is affected by temperature
• Beyond the optimum temperature, rate of
enzyme activity deceases.
• Until it is completely denatured by the extreme
heat
NOTE:
Describe the
enzyme activity with
respect to the Rate-
Temperature Graph
• Increase in temperature increases the
vibrations of the atoms in the enzymes.
• Beyond the OT, the vibrations are so
violent that they break the hydrogen bonds
that hold the 3-D structrure in place.
• The enzyme loses its shape and active site
• The enzyme is DENATURED.
Increasing temp beyond optimum temp.

14. (4) Enzymes are affected by pH(4) Enzymes are affected by pH
• Different enzymes have
different optimum pH.
• Enzymes are affected
by the acidity or
alkalinity of the solutions
• M indicates the optimum
pH when the rate of
reaction is the highest

15. Different enzymes have different optimum pH
• Enzymes that work best at ACIDIC conditions
 Renin and Pepsin: Found in the stomach
• Enzymes that work best at ALKALINE conditions
 Intestinal Enzymes
• Enzymes that work best at NEUTRAL conditions
 Amylase
ExamplesExamples

16. Different enzymes have different optimum pH

17. How enzyme activity is affected by pH
At pH slightly above or below the optimumAt pH slightly above or below the optimum
• Enzyme activity reduces when the
conditions are slightly more acidic or
alkaline than the optimum pH
• Slight changes in the pH brings about reversible
changes
• Changes can be restored by bringing enzyme back to
the optimum pH

18. How enzyme activity is affected by pH
At extreme pH conditionsAt extreme pH conditions
• Enzymes are DENATURED
• Extreme changes in the pH causes:
 A change in the charges at the active sites which
repels the substrate molecules, preventing them from
binding.
 The irreversible alteration to the bonds that holds the
shape of the enzyme. Enzyme thus loses its original
3-D structure. The active site loses its shape.

19. (5) Some enzymes catalyze reversible reactions(5) Some enzymes catalyze reversible reactions
AA BB CC DD+ +
Reactants Products
Products Reactants
• Some enzymes catalyse both reactions until equilibrium
is reached.
• Reactions will proceed in the direction where the products
are constantly being removed
• E.g formation of glucose during photosynthesis

20. (6) Some enzymes require co-enzymes(6) Some enzymes require co-enzymes
•Some enzymes require co-enzymes to be bound
to them before they can catalyse reactions
Co-enzymes
•Small, non-protein, organic “helper” molecules

21. (7) Enzymes are inhibited by inhibitors(7) Enzymes are inhibited by inhibitors
Type 1 (Competitive)
Substrate is prevented
from binding to active site
by inhibitor
Type 1 (Competitive)
Substrate is prevented
from binding to active site
by inhibitor
Type 2 (Non-competitive)
Binding of inhibitor does not
prevent the binding of substrate
but slows down reaction speed
Type 2 (Non-competitive)
Binding of inhibitor does not
prevent the binding of substrate
but slows down reaction speed