#17.2 Enzymes - Syllabus 2016 - 2018

3.1    Mode of action of enzymes
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.