Enzymes are biological catalysts which speed up chemical reactions without being used up in the
reaction. There extra and intracellular enzymes all over the body which can help in reactions such as
digestion and respiration, or produce tissues.
Enzymes work by lowering the activation energy of reactions, allowing them to happen at body
temperature as the molecules do not need as much kinetic energy to effect the reaction. When
breaking down a molecule, the shape of the active site will put strain on some of the bonds in the
substrate, effectively pulling them apart, which helps the substrate break into smaller molecules.
When joining two molecules together, the enzymes forces the two substrates together and reduces
the effects of repulsion between them so that they can bond.
The shape of the enzyme’s active site is important as it is specific to a specific substrate which fits
into it. There are two different theories about how the enzyme and substrate fit together. The lock
and key model says that the substrate and active site of the enzyme fit together perfectly, in the
same way a key fits a lock. The induced fit model says that, in addition to being the right shape to fit
into the active site, the substrate must also make it change shape in the right way to bond with it.
This is because, while the substrate and active site are similarly shaped, they are not perfect and the
shape of the active site must change a little to accommodate the substrate. This theory explains
better why only one single substrate fits into each type of enzyme.
Enzymes are made of proteins, whose tertiary structure determines their shape (tertiary structure
depends on primary and secondary structure). If the structure is altered the substrate will not fit
into the active site and the enzyme will not be able to carry out its function. If that happens in a
reaction catalysed by enzymes, the rate of reaction will fall as there will be no functional catalyst. If
the shape is permanently changed, the enzyme is denatured. This can happen in a number of ways.
In accordance with collision theory, rate of reaction increases when temperature increases in an
enzyme controlled reaction. This is because the molecules have more kinetic energy, so move faster,
which makes substrate molecules more likely to collide with enzymes and other substrate molecules
with enough activation energy to effect a reaction. The increase in rate against temperature is fairly
linear, up to an optimum temperature where rate of reaction is at its highest. After this temperature
rate of reaction falls dramatically. This is because the enzymes have too much kinetic energy and
some of the bonds in them breaks. This distorts the shape of the active site and denatures the
enzyme.
The graph formed for the rate of reaction against pH in an enzyme controlled reaction is symmetrical
around the optimum point. Enzymes have an optimum pH, at which the rate of reaction is highest,
and the further from it the pH is the lower the rate of reaction. This is because pH is determined by
the concentration of H- and OH+ ions in a substance. These ions can break hydrogen bonds and ionic
bonds. This denatures the enzyme by changing the shape of the active site so substrate molecules no
longer fit into it.
If the substrate concentration is increased, the rate of reaction will increase, forming a linear graph
up to a point where the rate of reaction stops increasing. This is because there will be more
collisions of enzymes with substrate molecules as temperature Increases. The rate of reaction
plateaus because there is a fixed amount of enzymes, which become saturated. This means there are
enough substrate molecules that all the active sites are being used at once, so adding more
substrate would not add to the amount of molecules being built or broken down in a fixed amount
of time.
If enzyme concentration is increased, rate of reaction will increase due to the increased likelihood of
enzyme and substrate molecules colliding. After a point the rate of reaction levels out because
reaction. There extra and intracellular enzymes all over the body which can help in reactions such as
digestion and respiration, or produce tissues.
Enzymes work by lowering the activation energy of reactions, allowing them to happen at body
temperature as the molecules do not need as much kinetic energy to effect the reaction. When
breaking down a molecule, the shape of the active site will put strain on some of the bonds in the
substrate, effectively pulling them apart, which helps the substrate break into smaller molecules.
When joining two molecules together, the enzymes forces the two substrates together and reduces
the effects of repulsion between them so that they can bond.
The shape of the enzyme’s active site is important as it is specific to a specific substrate which fits
into it. There are two different theories about how the enzyme and substrate fit together. The lock
and key model says that the substrate and active site of the enzyme fit together perfectly, in the
same way a key fits a lock. The induced fit model says that, in addition to being the right shape to fit
into the active site, the substrate must also make it change shape in the right way to bond with it.
This is because, while the substrate and active site are similarly shaped, they are not perfect and the
shape of the active site must change a little to accommodate the substrate. This theory explains
better why only one single substrate fits into each type of enzyme.
Enzymes are made of proteins, whose tertiary structure determines their shape (tertiary structure
depends on primary and secondary structure). If the structure is altered the substrate will not fit
into the active site and the enzyme will not be able to carry out its function. If that happens in a
reaction catalysed by enzymes, the rate of reaction will fall as there will be no functional catalyst. If
the shape is permanently changed, the enzyme is denatured. This can happen in a number of ways.
In accordance with collision theory, rate of reaction increases when temperature increases in an
enzyme controlled reaction. This is because the molecules have more kinetic energy, so move faster,
which makes substrate molecules more likely to collide with enzymes and other substrate molecules
with enough activation energy to effect a reaction. The increase in rate against temperature is fairly
linear, up to an optimum temperature where rate of reaction is at its highest. After this temperature
rate of reaction falls dramatically. This is because the enzymes have too much kinetic energy and
some of the bonds in them breaks. This distorts the shape of the active site and denatures the
enzyme.
The graph formed for the rate of reaction against pH in an enzyme controlled reaction is symmetrical
around the optimum point. Enzymes have an optimum pH, at which the rate of reaction is highest,
and the further from it the pH is the lower the rate of reaction. This is because pH is determined by
the concentration of H- and OH+ ions in a substance. These ions can break hydrogen bonds and ionic
bonds. This denatures the enzyme by changing the shape of the active site so substrate molecules no
longer fit into it.
If the substrate concentration is increased, the rate of reaction will increase, forming a linear graph
up to a point where the rate of reaction stops increasing. This is because there will be more
collisions of enzymes with substrate molecules as temperature Increases. The rate of reaction
plateaus because there is a fixed amount of enzymes, which become saturated. This means there are
enough substrate molecules that all the active sites are being used at once, so adding more
substrate would not add to the amount of molecules being built or broken down in a fixed amount
of time.
If enzyme concentration is increased, rate of reaction will increase due to the increased likelihood of
enzyme and substrate molecules colliding. After a point the rate of reaction levels out because
