Enzymes are globular
proteins: they have a
tertiary structure with
many hydrogen bonds
holding them, they are
also soluble in water
which helps them
Classification of enzymes
Enzymes are classified by the type of reaction they catalyse.
The name of an enzyme identifies the reacting substance.(most
enzymes end in "ase")
For example sucrase catalyzes the hydrolysis of sucrose.
The name also describes the function of the enzyme.
For example oxidises catalyze oxidation reactions.
Speeding up reactions
As biological catalysts
they are able to speed
reactions without being
used up in the process
which helps them to
reactions with a few
added since they can
They have a specific
active site for a specific
substrate to be formed
or broken down.
do this by
Inhibitors are substances which have a
similar structure to the enzyme substrates
hence fitting in its activesite and stopping
its activity permanently or temporarily.
There are two main types of inhibitors, they
are: competitive inhibitors and in
competitive inhibitors .
What are competitive inhibitors??
If an inhibitor molecule binds with the activesite
of the enzyme then there is competition
between the inhibitor and the substrate.
If there is more of the substrate then there is
more chance of collision with the active sit than
If other wise then the inhibitor binds with the
active site and inhibits its function
They are said to be reversible as they can be
reversed by increasing substrate concentration.
What are non-competitive inhibitors?
These are inhibitors which bind permanently
to the enzymes active sit and there fore no
competition occurring between the
substrate and the inhibitor.
They are irreversible as they bind to another
part of the enzyme thus altering the position
of hydrogen bonds and changing the 3D
shape of the enzyme. This changes the
shape of the active site and makes it
impossible for the substrate to fit in, therefore
permanently inhibiting enzymes function.
They are non-protein substances that work by altering the shape of an
enzyme so as to make it participate effectively during an enzymatic
Cofactors ensure that an enzyme controlled reaction takes place at an
There are mainly two types of Cofactors: coenzyme and metal ions
Coenzymes are organic molecules that bind to the active with the
substrate to help reactions occur. They can be recycled and used again.
Metal ions are known as the common Cofactors. They speed up the
formation of the enzyme substrate complex by altering the charge in the
active site or the end shape of the complex
A coenzyme which is a permanent part of an enzyme is called a
An important group of coenzymes are vitamins. Most Coenzymes are
obtained from vitamins. For example, vitamin B12 acts as coenzyme.
They are also obtained from nucleotides such as adenosine triphosphate
In the absence of the right cofactor, the enzyme would not function
Blue line, with
respect to product
and red line with
respect to reactants
Factors Affecting reaction rate
Temperature: enzymes work best at an optimum temperature.
Below this, an increase in temperature provides more kinetic energy to the molecules
involved. The numbers of collisions between enzyme and substrate will increase so the
rate will too.
Above the optimum temperature, and the enzymes are denatured. Bonds holding the
structure together will be broken and the active site loses its shape and will no longer
pH: as with temperature, enzymes have an optimum pH. If the pH changes much from
the optimum, the chemical nature of the amino acids can change.
This may result in a change in the bonds and so the tertiary structure may break down.
The active site will be disrupted and the enzyme will be denatured.
Enzyme concentration: at low enzyme concentration there is great competition for the
active sites and the rate of reaction is low. As the enzyme concentration increases,
there are more active sites and the reaction can proceed at a faster rate.
Eventually, increasing the enzyme concentration beyond a certain point has no effect
because the substrate concentration becomes the limiting factor.
Substrate concentration: at a low substrate concentration there are many active sites
that are not occupied. This means that the reaction rate is low.
When more substrate molecules are added, more enzyme-substrate complexes can be
formed. As there are more active sites, and the rate of reaction increases.
Eventually, increasing the substrate concentration yet further will have no effect. The
active sites will be saturated so no more enzyme-substrate complexes can be formed.
used to pre-digest proteins during the
manufacture of baby foods
used - together with protease - in
biological detergents to break down digest - the substances in stains into
smaller, water soluble substances
used to convert starch syrup, which is
relatively cheap, into sugar syrup,
which is more valuable - for example,
as an ingredient in sports drinks
used to convert glucose syrup into
fructose syrup - fructose is sweeter
than glucose, so it can be used in
smaller amounts in slimming foods