Enzymes
We couldn’t live with out them!
Intermediate 2
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What is an enzyme?
• Known as a BIOLOGICAL CATALYST
• Catalyst is something that speeds up a
chemical reaction
• Biological catalyst speeds up reactions in
living cells
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Activation Energy
• Do this by lowering the ACTIVATION
ENERGY - the energy required for a
reaction to begin
Energy
Uncatalysed reaction
Catalysed reaction
Progress of reaction
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Properties of Enzymes
• They are made of PROTEIN
• They are not changed by the reactions
they speed up
• They are SPECIFIC- means that only one
particular enzyme will work with one
particular substrate
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Other terms you need to know
• Substrate – the substance that the
enzyme works on e.g. Amylase the
substrate is starch
• Product – the substance that is made by
the reaction e.g. Breakdown of starch by
Amylase the product is Maltose
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CATALASE
• Found in animal and plant cells
• Needed to speed up the breakdown of
HYDROGEN PEROXIDE
• Breaks it down to OXYGEN and WATER
• The word equation for this looks like this
OXYGEN AND WATER
HYDROGEN PEROXIDE
CATALASE
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HPCOW
Amylase
• Found in saliva and in the pancreas
• Break down enzyme
• Breaks STARCH down to MALTOSE
• Word equation looks like this
STARCH
MALTOSE
AMYLASE
SAM
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Potato Phosphorylase
• Synthesis enzyme (builds up)
• Builds Glucose-1-Phosphate molecules
into Starch
• The formation of starch is tested using
iodine solution
Starch
Glucose-1-Phosphate
Phosphorylase
G1PPS
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More about Specific
• This means amylase will only breakdown
starch
• Catalase will only breakdown hydrogen
peroxide
• Amylase will NOT breakdown hydrogen
peroxide
• Catalase will NOT breakdown starch
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Lock and Key
• All enzymes have a special shaped area
that fits onto their substrate
• This area is called the ACTIVE SITE
• This Active site will fit onto the substrate
while the reaction takes place
• Because it fits like a lock and key we call
this the lock and key mechanism
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Model of Lock and Key
substrate
products
enzyme substrate complex
active site
enzyme
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enzyme – unchanged
Effect of Temperature
• Speed of reaction increases until an
Optimum temperature is reached
• Optimum temperature is the temperature
at which the enzyme works best
• After this point the rate of reaction
decreases until there is no reaction
• At this point enzyme is said to be
DENATURED – active site destroyed
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Effect of pH
• Most enzymes have an optimum pH of 7
• Some enzymes have a different optimum
pH for example pepsin has an optimum pH
of 2
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More to do
• Click on links to go to website and do
Biology keystage 3 lessons 14,15,16,39
and 40
http://lgfl.skoool.co.uk/keystage3
• Also go to BBC bitesize standard grade
biology topic investigating cells Enzymes
and Aerobic Respiration
http://www.bbc.co.uk/scotland/education/bitesize/
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