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
reaction
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
cells
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
‘lock’)
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
again
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
enzymes)
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
decreases
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
powders
Producing antibiotic
penicillin
Use of enzymes in: germination of seeds
enzymes in seeds
breakdown stored food
substance into soluble end
products which can be
translocated to growing
regions
starch is broken down to
maltose by the enzyme
amylase
fats/oils are broken down
by lipase to fatty acids and
glycerol
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
powders
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 &
glycerol
presence of protease breaks
down protein stain into amino
acids
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
activity
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
penicillin
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
required
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
48.