enzymes are protein molecules that are able to catalyse a biological reaction
TRANSCRIPT
Enzymes are protein molecules that are able to catalyse a biological reaction.
Each type of enzyme is highly specific for only one type of a reaction
With the use of an enzyme the rate of a particular reaction can increase by a factor greater than 108
They work by providing an alternative pathway with a lower activation energy
More reactant molecules then have the necessary minimum activation energy
The specificity of the enzyme depends on their tertiary and quaternary structure.
The substrate (reactant molecule) binds to a part of the enzyme known as the active site
The active site is able to change shape allowing the substrate to fit effectively and this is known as the induced fit theory
Inhibitors are substances that slow down the rate of an enzyme catalysed reaction
Competitive inhibitors resemble the substrate in shape but they are unable to react
They occupy the active site making it less accessible to the substrate
As the concentration of the substrate molecules increases the effect of the competitive inhibitors decreases
Competitive inhibition
Non-competitive inhibitors bind to the enzyme but not to the active site
The enzyme then changes shape and the substrates are no longer able to bind
With this type of inhibitor increasing the concentration of the substrate molecules will have no effect as the non-competitive inhibitors don’t bind to the active site
Non-competitive inhibition
At low substrate concentrations the rate of the reaction is proportional to the concentration of the substrate
At high substrate concentrations the rate of the reaction reaches a maximum point known as Vmax
This means that that at low substrate concentrations there are enough active sites for the substrates to bind and react
When all the active sites are used the enzyme is not able to work any faster
This constant Km is the concentration of the substrate at half of the Vmax
It is always the same for a particular enzyme with a particular substrate
It indicates whether the enzyme functions appropriately at low substrate concentrations or whether high substrate concentrations are needed for the efficient catalysis
Lower Km → more efficient enzyme
Competitive vs Non-competitive
Competitive inhibitor Blocks active sites Same Vmax Larger Km
Non-competitive Enzyme changes shape Smaller Vmax Same Km
An increase in temperature at first increases the rate of the reaction until the optimum temperature is reached (usually 40°C)
Until then more reactants posses the necessary activation energy to react
After the optimum temperature is reached the enzyme starts to denaturate as the bonds holding the structure together break
At certain pH values there is a change in the charge of the amino acid which affects the bond and alters the structure of the enzyme making it inactive
Heavy metals “poison” the enzyme They react with the –SH group and
replace the hydrogen atom with a heavy metal atom, or ion altering once more the structure of the enzyme
Effect of temperature and pH on rate of enzyme activity