B3. Enzymes - IGCSEBiology-Dnl

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Transcript B3. Enzymes - IGCSEBiology-Dnl

Pg 39 - 48
What are enzymes?
 enzymes are proteins
that function as
biological catalysts
 a catalysts is a
substance that usually
speeds up the rate of a
chemical reaction and is
not changed by the
 thus enzymes speed up
the rate of metabolic
reactions in the cells
Enzymes work
 enzymes lower the minimum
amount of energy required for
chemical reaction to occur
(activation energy)
 this allows biochemical
reactions to take place at a faster
rate in the cells of living
organisms at body temperature
which is usually low
 enzymes catalyse metabolic
reactions (i.e. chemical
reactions that sustain life) in a
 metabolic reactions are either
breakdown reactions catabolism or build up
reactions - anabolism
Naming of Enzymes
 Enzyme are named
according to the reaction
they catalyse
 A suffix – ase is usually
added to the name of the
substrate of the reaction
catalysed by the enzyme
 Sometimes they are
given special names such
as catalase & amylase
 Catalase is the fastest
acting enzyme
How Enzymes Work
“Lock and Key” Model
 Each enzyme has a shape that allows it to
catalyse one reaction
 Reactant(s) in an enzyme – catalysed
reaction is/are called substrate(s)
 Enzyme’s molecule has a specific shape
which is complementary to that of a
substrate –this is called active site
The substrate fits into the active site of the
enzyme the same way a ‘key fits into a lock’ this is called “ lock and key” model
The substrate (the ‘key’) fits exactly into the
active site (the ‘key hole’) of the enzyme (the
An enzyme-substrate complex is formed.
The substrate undergoes a chemical change –
a new substance, the product, is formed
The product is released from the active site.
The free unaltered active site is ready to
receive fresh substrate.
General Properties of Enzymes
 enzymes are all Proteins
 enzymes are Specific in
reaction they catalyse
enzymes are not changed by
the reaction they catalyse i.e.
they can be used again and
enzymes are influenced by
change in temperature
enzymes are influenced by
change in pH
enzymes work best at
particular temperature (37 oC
in humans)and pH (pH 2 for
pepsin & pH 7 for most
Factors Affecting Enzyme Activity
 Enzyme activity is
determined by
measuring the rate of
reaction that the
enzyme catalyses
 This is usually
measured by
measuring the
products formed per
unit time
 Enzyme activity is
affected by;
 temperature,
 pH &
 substrate concentration
Effect of Temperature on Enzymes
 at low temperature (e.g. 0°C) enzyme activity is
low because the movement of molecules is slow
due to low kinetic energy
 the collision frequency between enzyme and
substrate is therefore low
 increasing the temperature, increases kinetic
energy of molecules thus speeding up their
movement, collision frequency between the
substrates and the enzymes increases therefore
enzyme activity increases
 maximum enzyme activity is at 40°C – due to
maximum collision frequency between enzymes
and substrates molecules – this is called
optimum temperature (i.e. the temperature at
which the enzyme works fastest)
 enzyme action decreases above 40°C because the
enzymes are denatured by excess temperature
(i.e. the shape of active site is altered & substrates
molecules can no longer fit into it)
 when all the enzymes are denatured, at 60°C,
enzyme activity stops
Effect of pH on Enzymes
 enzyme activity is greatest within a
narrow range of pH, since all the
enzymes are functioning normally
because their active sites have the
correct shape
 this is called the optimum pH
 change in pH from the optimum, alters
the shape of active site thus affecting
the ability of the substrates to bind to
the active site & so enzyme activity
 a major change in pH from the
optimum denatures the enzymes so
enzyme action stops
 What is the optimum pH for;
 enzyme X?
 enzyme Y?
Use of enzymes in: germination of seeds,
biological washing products & food industry
 Enzymes are widely used in
industry because;
 they work at lower temperature
than other catalysts thus
reducing cost of fuel
 they are not destroyed by the
reaction the catalyse, thus they
can be used over and over again
 Applications of enzymes in day –
to – day life include;
 Hydrolysis of stored food
during seed germinations
 Use of enzymes in food industry
such as juice extraction,
brewing industry to make beer
 Making of biological washing
 Producing antibiotic
Use of enzymes in: germination of seeds
 enzymes in seeds
breakdown stored food
substance into soluble end
products which can be
translocated to growing
 starch is broken down to
maltose by the enzyme
 fats/oils are broken down
by lipase to fatty acids and
 maltose & fatty acids are
respired to provide energy
for germination
Production of apple juice
 enzyme pectinase is
added to crushed apple
fruit pulp
 the enzyme breaks down
pectin in plant cell walls
releasing more juice
from the crushed apples
Use of enzymes in biological washing
 presence of enzymes in
biological washing powders
increase the efficiency of the
washing powder in removing
stains from clothes because:
stains may be protein or fat
which are not removable with
detergent only
presence of lipase breaks down
fat stain into fatty acids &
presence of protease breaks
down protein stain into amino
fatty acids, glycerol & amino
acids are soluble in water thus
easily washed away
Controlling the temperature of the wash
 temperature of the wash
needs to be carefully
controlled because:
 high temperature
denatures enzymes , so
enzymes will not work
 at low temperature,
enzymes are inactive thus
they work slowly
 constant optimum
temperature such as 37 oC
maintains optimum
conditions for enzyme
Use of microorganisms & industrial fermenters to
manufacture the antibiotic
 industrial fermenters are large
metal tanks that uses
microorganisms to produce useful
products such as antibiotics such as
 the organism involved, fungus
Penicillium is added to the tank
together with nutrients such as sugar
& ammonium salts (or amino acids)
 Penicillium produce enzymes which
converts the substrate into
penicillin, antibiotic used to cure
bacterial infections
 sugar provide energy for respiration
while ammonium salt is used to
produce proteins & nucleic acids
Maintaining suitable conditions in the
industrial fermenters
 suitable conditions such as optimum
pH, optimum temperature and
supply of oxygen & nutrients are
 air is bubbled through to provide
oxygen for respiration
stirring using paddles keeps
microorganism suspended so they
always have access to nutrients & O2
and rolls the fungus into little pellets
making it easy to separate liquid from
the culture
water -cooled jacket maintains a
constant temperature of 24 oC
probes monitor the temperature &
pH in the tank. pH is maintained at
6.5 by adding alkalis where necessary
after 6 days, fermentation is complete
& the mixture is drained & filtered
penicillin is then extracted
Role of the fungus Penicillium in the
production of antibiotic penicillin
 fungus penicillium
produces enzymes that
converts the substrate
into penicillin,
antibiotic used to cure
bacterial infections
Revision activity
 After reading pages 39 -
48 of your biology
textbook and your lesson
notes, attempt Revision
Questions 1 - 4 on page