the end of the unit learners should be able to:
Describe the mode of action and factors
affecting enzymes and their importance for the existence of life.
Use a computer to plot graphs
of the rate of enzyme-controlled reaction and to determine Q10 of a given
Appreciate the importance of
planning and carrying out experiments under controlled conditions.
1.1 Criteria for naming enzymes
Enzymes are biological
catalyst produced by a living organism to control the speed of specific
biochemical reactions (metabolism) by reducing its activation energy.
First, Individual enzymes are named by adding -ase to the name of the substrate with which they react.
The enzyme that controls urea
decomposition is called urease; those that control protein hydrolyses are known
A second way of naming
enzymes refers to the enzyme commission number (EC number) which is a numerical
classification scheme for enzymes based on the chemical reactions they catalyze.
As a system of enzyme
nomenclature, every EC number is associated with a recommended name for the
respective enzyme catalyzing a specific reaction.
· Catalyze redox reactions by
the transfer of hydrogen, oxygen or electrons from one molecule to another.
· Example: Oxidase catalyses
the addition of oxygen to hydrogen to form water.
· Catalyze group transfer
· The transfer occurs from one
molecule that will be the donor to another molecule that will be the acceptor.
Most of the time, the donor is a cofactor that is charged with the group about
to be transferred.
· Example: Hexokinase used in
· Catalyze reactions where
functional groups are added to break double bonds in molecules or the reverse
where double bonds are formed by the removal of functional groups.
· For example; Fructose
bisphosphate aldolase used in converting fructose 1,6-bisphospate to G3P and
DHAP by cutting C-C bond.
· Catalyze reactions that
transfer functional groups within a molecule so that isomeric forms are
· These enzymes allow for
structural or geometric changes within a compound. Sometime the interconversion
is carried out by an intramolecular oxidoreduction. In this case, one molecule
is both the hydrogen acceptor and donor, so there's no oxidized product.
· The lack of an oxidized
product is the reason this enzyme falls under this classification. The subclasses
are created under this category by the type of isomerism.
· For example: phosphoglucose
isomerase for converting glucose 6-phosphate to fructose 6-phosphate. Moving
chemical group inside the same substrate.
· A third way of naming enzymes
is by their specific names e.g. trypsin and pepsin are proteases.
· Pepsin, trypsin, and some
other enzymes possess, in addition, the peculiar property known as
autocatalysis, which permits them to cause their own formation from an inert
precursor called zymogen.
1.2 Characteristics of Enzymes
· Enzymes are globular
proteins. Enzymes speed up the rate of metabolic reactions.
· An enzyme allows the reaction
to go through a more stable transition state than would normally be the case.
· As a result, the rate of reaction
is increased. Enzymes lower the activation energy (Ea) required for reactions
to take place.
· In many chemical reactions,
the substrate will not be converted to a product unless it is temporarily given
some extra energy.
· This energy is called activation
energy i.e. the minimum energy required the make a reaction take place.