3.1 Mode of action of enzymes
3.2 Factors that affect enzyme action
3.2 Factors that affect enzyme action
Enzymes are essential for life to exist. Their mode of action and the factors that affect their activity are explored in this section. Prior knowledge for this section 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 section for candidates to gain experience of carrying out practical investigations and analysing and interpreting their results.
Learning Outcomes
Candidates should be able to:
3.1 Mode of action of enzymes
There are many different enzymes, each one specific to a particular reaction. This specificity is the key to understanding the efficient functioning of cells and living organisms.
a) explain that enzymes are globular proteins that catalyse metabolic reactions
b) state that enzymes function inside cells (intracellular enzymes) and outside cells (extracellular enzymes)
c) explain the mode of action of enzymes in terms of an active site, enzyme/substrate complex, lowering of activation energy and enzyme specificity (the lock and key hypothesis and the induced fit hypothesis should be included)
d) investigate the progress of an enzyme-catalysed reaction by measuring rates of formation of products (for example, using catalase) or rates of disappearance of substrate (for example, using amylase)
3.2 Factors that affect enzyme action
Investigating the effects of factors on enzyme activity gives opportunities for planning and carrying out experiments under controlled conditions.
a) 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
b) 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
c) explain the effects of reversible inhibitors, both competitive and non-competitive, on the rate of enzyme activity
d) investigate and explain the effect of immobilising an enzyme in alginate on its activity as compared with its activity when free in solution.
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