Enzymes are protein molecules that catalyze biological reactions. They work by lowering the activation energy of reactions, allowing more molecules to react. Enzymes are highly specific and their tertiary structure forms an active site that binds substrates. Inhibitors can bind the active site and prevent substrate binding (competitive) or bind elsewhere and alter the enzyme shape (non-competitive). The rate of enzyme reactions saturates at high substrate concentrations as active sites fill.

2. Enzymes are protein molecules that are able to
catalyse a biological reaction.

3.  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

4.  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

6.  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

7. Competitive inhibition

8.  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

9. Non-competitive inhibition

11.  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

12.  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

14. Say That Again Please
http://www.youtube.com/watch?v=q94TCTSXyv8&context=C47b5c79ADvjVQa
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15. Competitive vs Non-competitive
 Competitive inhibitor  Non-competitive
 Blocks active sites  Enzyme changes shape
 Same Vmax  Smaller Vmax
 Larger Km  Same Km

16.  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

17.  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

18. Effect of temperature and pH on
rate of enzyme activity