Cambridge (CIE) AS Your notes
Biology
Mode of Action of Enzymes
Contents
Enzymes
Enzyme Action
How Enzymes Work
Measuring Enzyme Activity
Colorimetry
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, Enzymes
Your notes
Enzymes as Proteins
Enzymes are biological catalysts
‘Biological’ because they function in living systems
‘Catalysts’ because they speed up the rate of chemical reactions without being
used up or changed
Enzymes are also globular proteins
Critical to the enzyme's function is the active site where the substrate binds
Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions
Virtually every metabolic reaction within living organisms is catalysed by an enzyme
– enzymes are therefore essential for life to exist
Enzymes can be intracellular or extracellular referring to whether they are active inside
or outside the cell respectively
Intracellular enzymes are produced and function inside the cell
Extracellular enzymes are secreted by cells and catalyse reactions outside cells
(e.g. digestive enzymes in the gut)
Enzymes Table
Intracellular Extracellular
Example Catalase Amylase
Function Hydrogen peroxide is produced as Digestion of food is carried out
a by-product of many cellular by extracellular enzymes
reactions
This is because macromolecules
It is harmful to cells of food are too large to enter
cells
Catalase converts hydrogen
peroxide into water and oxygen, Amylase is an an example of a
preventing cell damage digestive enzyme
It digests carbohydrates into
simple sugars
Examiner Tips and Tricks
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Biology
Mode of Action of Enzymes
Contents
Enzymes
Enzyme Action
How Enzymes Work
Measuring Enzyme Activity
Colorimetry
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 1
, Enzymes
Your notes
Enzymes as Proteins
Enzymes are biological catalysts
‘Biological’ because they function in living systems
‘Catalysts’ because they speed up the rate of chemical reactions without being
used up or changed
Enzymes are also globular proteins
Critical to the enzyme's function is the active site where the substrate binds
Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions
Virtually every metabolic reaction within living organisms is catalysed by an enzyme
– enzymes are therefore essential for life to exist
Enzymes can be intracellular or extracellular referring to whether they are active inside
or outside the cell respectively
Intracellular enzymes are produced and function inside the cell
Extracellular enzymes are secreted by cells and catalyse reactions outside cells
(e.g. digestive enzymes in the gut)
Enzymes Table
Intracellular Extracellular
Example Catalase Amylase
Function Hydrogen peroxide is produced as Digestion of food is carried out
a by-product of many cellular by extracellular enzymes
reactions
This is because macromolecules
It is harmful to cells of food are too large to enter
cells
Catalase converts hydrogen
peroxide into water and oxygen, Amylase is an an example of a
preventing cell damage digestive enzyme
It digests carbohydrates into
simple sugars
Examiner Tips and Tricks
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 2
