Enzymes are essential for life to exist. The mode of action of enzymes and the factors that affect their activity
are explored in this topic. Prior
... [Show More] knowledge for this topic is an understanding that an enzyme is a biological
catalyst that increases the rate of a reaction and remains unchanged when the reaction is complete.
There are many opportunities in this topic for candidates to gain experience of carrying out practical
investigations and analysing, interpreting and evaluating their results.
3.1 Mode of action of enzymes Learning outcomes
Candidates should be able to:
1 state that enzymes are globular proteins that catalyse reactions
inside cells (intracellular enzymes) or are secreted to catalyse
reactions outside cells (extracellular enzymes)
2 explain the mode of action of enzymes in terms of an active site,
enzyme–substrate complex, lowering of activation energy and
enzyme specificity, including the lock-and-key hypothesis and
the induced-fit hypothesis
3 investigate the progress of enzyme-catalysed reactions by
measuring rates of formation of products using catalase and
rates of disappearance of substrate using amylase
4 outline the use of a colorimeter for measuring the progress of
enzyme-catalysed reactions that involve colour changes
3.2 Factors that affect enzyme
action
Learning outcomes
Candidates should be able to:
1 investigate and explain the effects of the following factors on
the rate of enzyme-catalysed reactions:
• temperature
• pH (using buffer solutions)
• enzyme concentration
• substrate concentration
• inhibitor concentration
2 explain that the maximum rate of reaction (Vmax) is used to
derive the Michaelis–Menten constant (Km), which is used to
compare the affinity of different enzymes for their substrates
3 explain the effects of reversible inhibitors, both competitive and
non-competitive, on enzyme activity
4 investigate the difference in activity between an enzyme
immobilised in alginate and the same enzyme free in solution,
and state the advantages of using immobilised enzymes [Show Less]