Enzymes
Structure of enzymes
Enzymes increase the rate of reactions, so are called biological catalysts.
Intracellular example = catalase binds to hydrogen peroxide and speeds up
the its breakdown to hydrogen and oxygen
Extracellular example = amylase is produced in the pancreas and is released
into the small intestine to catalyse the breakdown of starch molecules into
Maltose.
Majority of enzymes are globular proteins
They contain hydrophilic amino acids on their surface
Hydrophobic amino acids are buried in the centre of the protein
This makes globular proteins soluble in water.
Active site = location where the substrate attaches to. The tertiary structure of
the active site is complementary to the substrate. Therefore, each enzyme is
specific to its substrate.
Enzyme-substrate complex = point where the substrate attaches to the
enzyme.
Enzyme-product complex = product is in active site but not released yet
Once attached, amino acids on the surface of the active site form temporary
bonds with the substrate molecule, which helps lower the activation energy.
The enzyme catalyses the reaction to form the enzyme-product
complex. Products are then released from the active site.
Enzymes provide a pathway for a reaction with a lower activation energy
barrier. Therefore, more substrate molecules have enough energy to cross the
activation energy barrier.
Because enzymes can only fit to a specific substrate, the substrate is close
enough to react without excessive heat.
Induced fit model
The tertiary structure of the active site changes as the substrate approaches.
As the substrate starts to form bonds with the amino acids in the active
site, the tertiary structure adjusts and the active site moulds itself tightly
around the substrate. Destabilising of bonds in substrate forms enzyme-
product complex.
The change in shape ensures the substrate fits perfectly.
, The bonds that the substrate forms with the active site help to catalyse the
reaction.
Molecules that aren’t the correct substrate can’t form the bonds with specific
amino acids in the active site. Therefore, the tertiary structure doesn’t change
and the substrate can’t fit.
Previous lock and key model suggested the shape of the active site does not
change when substrate binds.
Measuring the rate of enzyme-controlled reactions
To measure the rate of reaction at a given point, we place a tangent that just
touches the curve at the desired point.
The rate of an enzyme-controlled reaction depends on the frequency of
successful collisions between the substrate and active site.
Explaining the rate of reaction graph:
At the start, we have many substrate molecules – high frequency of
successful collisions. Rapid rate of reaction
As the reaction progresses, some substrate molecules are converted into
the products. There are less substrate molecules so fewer successful
collisions.
At a certain point, all substrate molecules have been converted into
products.
Structure of enzymes
Enzymes increase the rate of reactions, so are called biological catalysts.
Intracellular example = catalase binds to hydrogen peroxide and speeds up
the its breakdown to hydrogen and oxygen
Extracellular example = amylase is produced in the pancreas and is released
into the small intestine to catalyse the breakdown of starch molecules into
Maltose.
Majority of enzymes are globular proteins
They contain hydrophilic amino acids on their surface
Hydrophobic amino acids are buried in the centre of the protein
This makes globular proteins soluble in water.
Active site = location where the substrate attaches to. The tertiary structure of
the active site is complementary to the substrate. Therefore, each enzyme is
specific to its substrate.
Enzyme-substrate complex = point where the substrate attaches to the
enzyme.
Enzyme-product complex = product is in active site but not released yet
Once attached, amino acids on the surface of the active site form temporary
bonds with the substrate molecule, which helps lower the activation energy.
The enzyme catalyses the reaction to form the enzyme-product
complex. Products are then released from the active site.
Enzymes provide a pathway for a reaction with a lower activation energy
barrier. Therefore, more substrate molecules have enough energy to cross the
activation energy barrier.
Because enzymes can only fit to a specific substrate, the substrate is close
enough to react without excessive heat.
Induced fit model
The tertiary structure of the active site changes as the substrate approaches.
As the substrate starts to form bonds with the amino acids in the active
site, the tertiary structure adjusts and the active site moulds itself tightly
around the substrate. Destabilising of bonds in substrate forms enzyme-
product complex.
The change in shape ensures the substrate fits perfectly.
, The bonds that the substrate forms with the active site help to catalyse the
reaction.
Molecules that aren’t the correct substrate can’t form the bonds with specific
amino acids in the active site. Therefore, the tertiary structure doesn’t change
and the substrate can’t fit.
Previous lock and key model suggested the shape of the active site does not
change when substrate binds.
Measuring the rate of enzyme-controlled reactions
To measure the rate of reaction at a given point, we place a tangent that just
touches the curve at the desired point.
The rate of an enzyme-controlled reaction depends on the frequency of
successful collisions between the substrate and active site.
Explaining the rate of reaction graph:
At the start, we have many substrate molecules – high frequency of
successful collisions. Rapid rate of reaction
As the reaction progresses, some substrate molecules are converted into
the products. There are less substrate molecules so fewer successful
collisions.
At a certain point, all substrate molecules have been converted into
products.
