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LEARNING OUTCOMES
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State what enzyme are
Explain why enzymes are needed in life processes
List the general characteristics of enzymes
Relate the name of enzyme to substrate
State sites where enzymes are synthesised
State the meaning of intracellular enzymes and extracellular
enzymes
Explain the involvement of specific organelles in the
production of extracellular enzymes
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Explain the effects of pH,temperature,enzyme concentration and
substrate concentration on enzyme activity
Explain the mechanism of enzyme action
Relate the mechanism of enzyme action with
pH,temperature,enzyme concentration and substrate concentration
Explain the uses of enzymes in daily life and industry using
examples
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Enzymes are protein
Enzymes are biological catalyst that speed up the rate of
biochemical reactions in the cells
Chemical reactions that occur within a living organism are called
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Metabolic reaction starts with the substrate and ends with product
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metabolism
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a)
b)
Speed up the rates of chemical reaction but remains unchanged at
the end of the reaction
Not destroyed by the reactions they catalyse
Highly specific that is each enzyme can only catalyse one kind of
substrate
Needed in small quantities because they are not used up but
released at the end of a reaction
Enzyme-catalyses reaction are reversible
Can be slowed down or completely stopped by inhibitors.
-e.g. : heavy metals such as lead and mercury
Require helper molecules called cofactors
Cofactors are divide by two:
organic cofactor like water soluble vitamin
Inorganic cofactor like ferum and copper
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An enzyme is named according to the name of the substrate it
catalyses
Other enzyme were named before a systematic way of naming
enzyme was formed
-e.g. : pepsin, trypsin and rennin
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By adding suffix -ase at the end of the name of their substrate
Enzyme for catalysing the hydrolysis
Example :
substrate
enzymes
products
lactose
lactase
glucose +
galactose
maltose
maltase
Glucose
cellulose
cellulase
Glucose
lipid
lipase
Glycerol + fatty
acid
starch
amylase
Maltose
protein
protease
Pepton +
polypeptide
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Ribosomes are attached to the roughed endoplasmic reticulum.
Information for the synthesis of enzyme is carried by DNA
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The different of bases in DNA are codes to make different protein
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RNA is formed to translate the codes into a sequence of amino acids
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Amino acids are bonded together to form specific enzyme according
to the DNA’s codes
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Intracellular : synthesised and retained in the cell for the use of cell
itself
: found in the cytoplasm, nucleus, mitochondria and
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chloroplast
Example : 1) oxydoreductase catalyse biological oxidation
2) reduction in the mitochondria
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Extracellular : synthesised in the cell but secreted from the cell to
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work
externally
Example : 1) digestive enzyme produced by the pancreas are not
used by
cells in the pancreas but are transported to the
duodenum
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Protein/Enzymes are synthesized in the ribosomes are
transported through the spaces between the rough
endoplasmic reticulum
Protein depart from the RER wrapped in vesicles that bud off
from the sides of the RER
These transport vesicles fuse with the membrane of the Golgi
apparatus
Secretory vesicles containing these modified protein bud off
from the Golgi membrane and travel to the plasma membrane
These vesicles will then fuse with the plasma membrane
before releasing the proteins outside the cells as enzymes.
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Enzymes are complex protein made of one or more polypeptide
chains
These polypeptide chain are folded into three-dimensional shape
which include a pocket called an active site
The ‘lock and key’ hypothesis
The ‘substrate’ molecule represent the ‘key’
The ‘enzyme’ molecule represent the ‘lock’
The substrate molecule binds to the active site to form an enzymesubstrate complex
The enzyme catalyses the substrate to form products, then leave the
active site
Enzyme molecule is now free to bind to more substrate molecules
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Temperature
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At low temperatures, an enzyme-catalysed reaction takes place
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slowly
For every 10°C rise in temperature, the rate of reaction is doubled
However, this is only true up to the optimum temperature
Optimum temperature is the temperature at which an enzyme
catalyses a reaction at the maximum rate
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Any increase in temperature will no longer increase the rate of
reaction because the bonds that hold enzyme molecules together
begin to break at high temperature, thus altering the threedimensional shape eventually destroying active site
Enzymes lose their activities and are said to be denatured
So, organisms cannot survive at temperatures above 40°C
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Ph
The optimum pH is the pH at which the rate of reaction is at the
maximum
A change in pH can alter the charges on the active sites of the
enzyme and the substrate surfaces,it can reduce the ability of both
molecules to bind each other
Pepsin can function in an acidic condition (pH 2) within in the
stomach
Trypsin can function in alkaline condition (pH 8.5) within the
duodenum
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Substrate concentration
Increase in substrate concentration, more substrate molecule are
available to bind the active sites of the enzyme
Hence, more products will be produced
Because more chances of collision between the substrate molecule
and the enzyme molecules for a catalytic reaction to take place
In increase in substrate concentration will only speed up the reaction
if there are enough enzyme molecules to catalyse the additional
substrate molecules
The rate of reaction is directly proportional to the substrate
concentration until the reaction reaches a maximum rate
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After maximum rate, all active site of the enzyme molecules are
filled and engaged in catalysis
The enzyme is said to be saturated
The concentration of enzyme becomes a limiting factor
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Enzyme concentration
When the concentration of an enzyme increases,more enzyme
molecules are available
The rate of of reaction will increase only if there is abundant supply
of substrate molecules and other factors are constant because more
active sites are made available for the catalytic reaction.
The rate of reaction is directly proportional to the concentration of
the enzyme present until a maximum rate is achieved .
After the maximum rate,the doncentration of substrate becomes a
limiting factor.
If the concentration of enzyme is doubled,the amount of substrate
molecules also doubled.
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The uses of enzymes
Can as catalysts in industries
The use of enzyme in
industrial processes is known
as enzyme technology.
Enzyme are use widely in our
daily life
be use
enzymes
uses
protease
Tenderise meat
amylase
To convert starch to sugar in the making of
syrup
lipase
Ripening the cheese
In
detergent
Effectively dissolve protein stain