Enzymes are biological catalysts that increase the rate of chemical reactions without being used up. They are proteins folded into complex shapes with active sites that substrates fit into like locks and keys. Enzymes are usually named for their substrates with the ending "-ase", such as lipase and proteases. Enzymes have five key characteristics: they are always proteins, are specific to reactions, can be reused, are denatured at 50°C, and have optimal pH levels. They are made inside cells and can work inside or outside of cells to speed chemical reactions. Enzymes are widely used in industry due to their ability to work at low temperatures and only be needed in small amounts.

1. ENZYMES
 Enzymes are biological catalysts.
Catalysts are substances that increase the rate
of chemical reactions without being used up.
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2. Enzymes
 Enzymes are also proteins that are folded
into complex shapes.
These complex shapes allow smaller molecules
called substrate molecules to fit in them.
The place where these substrate molecules fit
is called active site.
The substrate and the enzyme fit together at the active site like a lock
and a key.
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3.  Enzymes that exist in nature are usually
named for their substrates, and these are
given the ending –ase.
The enzyme Lipase, for example works on fatty
lipids.
Proteases breaks down proteins.
Carbohydrases breaks down carbohydrates.
Enzymes
However some of the first enzymes discovered were not named this
way. E.g. pepsin, which breaks down proteins.3

4.  Here is an example of a reaction which is
controlled by an enzyme:
NB: The arrows in the above reaction point in both
directions. This means that the reaction is
reversible; maltose can be turned into glucose, or
glucose into maltose. The enzyme will work both
ways.
Enzymes
Maltose Glucose
Maltase
(enzyme)
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5.  Enzymes have five important characteristics:
1. Enzymes are always proteins.
This is one reason why we
need proteins in our diet.
Enzymes
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6. 2. Enzymes are specific.
Each enzyme controls one particular reaction,
or type of reaction. For example maltase will act
only on maltose, and sucrase on sucrose.
Enzymes
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7. 3. Enzymes can be used over and over again.
This is because they are not changed by the
reaction in which they take part.
Enzymes
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8. 4. Enzymes are denatured at 50 degrees
Celsius.
Enzymes are affected by temperature. Usually
a rise in temperature increases chemical
reactions while a fall in temperature slows them
down.
However above 50 degrees the enzymes stop
working because their shape is changed – they
become denatured.
The optimum temperature for enzymes is
about 40 degrees.
Enzymes
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9. 5. Enzymes are affected by pH.
Acid or alkaline conditions change the chemical
properties of proteins, including enzymes. Most
enzymes work best at a particular level of
acidity or alkalinity (optimum pH).
The protein-digesting enzyme in your stomach
(pepsin), for example works well at an acidity of
pH2. Amylase (saliva enzyme) does not work
well at this pH. Inside the cells, most enzymes
work at pH7.
Unlike temperature, pH does not permanently
Enzymes
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10.  Enzymes are made inside cells. Once formed,
the enzyme may leave the cell and work
outside it.
Such enzymes are called extracellular
enzymes.
 Other enzymes work inside the cell. They are
called intracellular enzymes.
The job is to speed up the chemical reactions
happening inside our cells.
Enzymes
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11. Enzymes are used in industry because they are
cheap. They do not need high temperatures to
work and therefore decrease the cost spent on
fuels in industry.
Furthermore enzymes can be re-used and so
are needed in small amounts.
Enzymes
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12.  Biological washing powder:
These contain proteases so as to remove
stains which contain proteins (e.g. sweat).
These washing liquids work at quite low
temperatures. This is more economical and
does not damage the fabric or cause dye to run.
Using boiling water would kill the enzymes.
Enzymes
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13.  Extracting plant juices:
Cellulases are enzymes that break down plant
cell walls. These are used to ‘soften’ fruit or
vegetables for juice removal, removal of seed
coats from cereal grains and extracting agar
jelly from seaweed.
Enzymes
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14.  Fermentation:
Enzymes from bacteria or fungi are used in
fermentation to make beer, wine and vinegar.
Cheese involves the fermentation of milk or
cream.
Enzymes
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