Download Enzymes

Topic 4: Chapter 5
Enzymes – Part 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
(1) Enzymes Speed up chemical reactions
Energy
Activation Energy
with enzyme
Activation
Energy without
enzyme
Substrate
Products:
Time
• By lowering the activation energy needed to
start the reaction.
(2) Enzymes are required in minute amounts
Chemically unchanged
Sucrose
Sucrase
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
(3) Enzymes are highly specific
Starch
Maltose
Amylase
Maltase
Maltose
Glucose + Glucose
• 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”.
• 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.
Active
Sites
• 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
Substrate
Enzyme
Enzyme-Substrate Complex
Products + Enzyme
Anabolic Reaction - Synthesis
Catabolic Reaction - Hydrolysis
Lock
and Key
The
Hypothesis
• The substrate binds to a free enzyme with a
complementary active site to form the enzymesubstrate 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
(4) Enzymes are affected by temperature
• Enzymes can function
over a range of
temperatures.
• But all enzymes have
their own optimum
temperature.
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 37-40oC, near
body temperature.
Enzymes of thermophilic bacteria that
live in hotsprings will have very high
optimum temperatures.
How enzyme activity is affected by temperature
NOTE:
Describe the
enzyme activity with
respect to the RateTemperature Graph
Increasing temp up to optimum temp.
• At low temperature, enzymes are INACTIVE.
• As temperature rises, the rate of enzyme activity
increases (usually 2x as active for every 10oC
rise).
• Enzyme reaching maximum rate of activity at OT
• 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 enzymesubstrate complex.
• Rate of formation of the products increases
up till the optimum temperature
How enzyme activity is affected by temperature
NOTE:
Describe the
enzyme activity with
respect to the RateTemperature Graph
Increasing temp beyond optimum temp.
• Beyond the optimum temperature, rate of
enzyme activity deceases.
• Until it is completely denatured by the extreme
heat
• 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.
(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
Different enzymes have different optimum pH
Examples
• 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
Different enzymes have different optimum pH
How enzyme activity is affected by pH
At 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
How enzyme activity is affected by pH
At 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.
(5) Some enzymes catalyze reversible reactions
Reactants
A
+
Products
B
Products
C
+
D
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
(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
(7) Enzymes are inhibited by inhibitors
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