, Enzymes
Enzymes are globular proteins that interact with substrate molecules
causing them to react at much faster rates without the need for harsh
environmental conditions. They have a specific area on the surface of the
molecule, called the active site. The tertiary structure of the active site is
crucial as its shape is complementary to the shape of the substrate
molecule. So, each type of enzyme is highly specific in its function, as it can
only catalyse a reaction involving the particular type of substrate molecule
that fits into its active site.
Enzymes are called biological catalysts because they speed up metabolic
reactions in living organisms.
Both anabolic (building up- for growth) & catabolic (breaking down)
reactions are catalysed by enzymes. Reactions usually happen as part of a
multi-step pathway. Metabolism is the sum of all the different reactions &
reaction pathways happening in a cell or an organism & can only happen due
to enzymes involved. The number of reactions an enzyme can catalyse per
second is the turnover number.
Enzymes are more specific than chemical catalysts. They do not produce
unwanted by products & rarely make mistakes. The cells in which they are
made &/or act can also regulate their production & activity to fit the needs
of the cell or organism at the time.
SUBSTRAT–ASE e.g. glycosidase catalyses breaking of glycosidic bonds
, The lock and key hypothesis
Early scientists came up with the ‘lock & key’ model which demonstrates
that a substrate fits into the enzymes active site like a key fits into a lock.
A model is a simple representation of a process.
1. The substrate molecules & enzyme molecules each have kinetic energy &
are constantly moving randomly.
2.The complementary substrate molecule fits into the enzymes active site.
Temporary hydrogen bonds hold the 2 together forming an enzyme-
substrate complex.
3.An enzyme-product complex is formed when a substrate molecule is
either broken into smaller product molecules or bonds form between
substrate molecules. The product(s) leave the active site as the molecules
have a slightly different shape from the substrate molecules.
Enzyme-product complex- enzyme molecule with product molecule(s) in its
active site. The 2 are joined temporarily by non covalent forces.
Enzyme-substrate
complex- enzyme
molecule with substrate
molecule(s) in its active
site. The 2 are joined
temporarily by non
covalent forces.
, Induced fit hypothesis
The ‘induced fit’
model is a better
theory. It helps to
explain why enzymes
are so specific &
only bond to one
particular substrate.
The active site still has a shape complementary to the shape of
the substrate molecule. However, on binding the active site
changes shape slightly to mould itself around the substrate
molecule. These subtle changes of shape are down to the side
chains (R groups) of the amino acids which give a more precise
conformation that exactly fits the substrate molecule. This
moulding enables the substrate to bind more effectively. Fitting
into the active site puts a strain on bonds in the substrate. This
strain means the substrate molecules break up more easily.
Enzymes are globular proteins that interact with substrate molecules
causing them to react at much faster rates without the need for harsh
environmental conditions. They have a specific area on the surface of the
molecule, called the active site. The tertiary structure of the active site is
crucial as its shape is complementary to the shape of the substrate
molecule. So, each type of enzyme is highly specific in its function, as it can
only catalyse a reaction involving the particular type of substrate molecule
that fits into its active site.
Enzymes are called biological catalysts because they speed up metabolic
reactions in living organisms.
Both anabolic (building up- for growth) & catabolic (breaking down)
reactions are catalysed by enzymes. Reactions usually happen as part of a
multi-step pathway. Metabolism is the sum of all the different reactions &
reaction pathways happening in a cell or an organism & can only happen due
to enzymes involved. The number of reactions an enzyme can catalyse per
second is the turnover number.
Enzymes are more specific than chemical catalysts. They do not produce
unwanted by products & rarely make mistakes. The cells in which they are
made &/or act can also regulate their production & activity to fit the needs
of the cell or organism at the time.
SUBSTRAT–ASE e.g. glycosidase catalyses breaking of glycosidic bonds
, The lock and key hypothesis
Early scientists came up with the ‘lock & key’ model which demonstrates
that a substrate fits into the enzymes active site like a key fits into a lock.
A model is a simple representation of a process.
1. The substrate molecules & enzyme molecules each have kinetic energy &
are constantly moving randomly.
2.The complementary substrate molecule fits into the enzymes active site.
Temporary hydrogen bonds hold the 2 together forming an enzyme-
substrate complex.
3.An enzyme-product complex is formed when a substrate molecule is
either broken into smaller product molecules or bonds form between
substrate molecules. The product(s) leave the active site as the molecules
have a slightly different shape from the substrate molecules.
Enzyme-product complex- enzyme molecule with product molecule(s) in its
active site. The 2 are joined temporarily by non covalent forces.
Enzyme-substrate
complex- enzyme
molecule with substrate
molecule(s) in its active
site. The 2 are joined
temporarily by non
covalent forces.
, Induced fit hypothesis
The ‘induced fit’
model is a better
theory. It helps to
explain why enzymes
are so specific &
only bond to one
particular substrate.
The active site still has a shape complementary to the shape of
the substrate molecule. However, on binding the active site
changes shape slightly to mould itself around the substrate
molecule. These subtle changes of shape are down to the side
chains (R groups) of the amino acids which give a more precise
conformation that exactly fits the substrate molecule. This
moulding enables the substrate to bind more effectively. Fitting
into the active site puts a strain on bonds in the substrate. This
strain means the substrate molecules break up more easily.
