Cambridge International A Level Biology Revision Guide

Chapter 3: Enzymes
BOX 3.2: Immobilised enzymes
Figure 3.15 shows one way in which enzymes can
be immobilised. The enzyme is mixed with a solution
of sodium alginate. Little droplets of this mixture are
then added to a solution of calcium chloride. The sodium
alginate and calcium chloride instantly react to form jelly,
which turns each droplet into a little bead. The jelly bead
contains the enzyme. The enzyme is held in the bead, or
immobilised.
These beads can be packed gently into a column. A liquid
containing the enzyme’s substrate can be allowed to trickle
steadily over them (Figure 3.16).
As the substrate runs over the surface of the beads, the
enzymes in the beads catalyse a reaction that converts the
substrate into product. The product continues to trickle
down the column, emerging from the bottom, where it can
be collected and purified.
milk
alginate beads containing
immobilised lactase
milk free of lactose
and lactase
mixture of sodium alginate
solution and lactase
65
Figure 3.16 Using immobilised enzyme to
modify milk.
When small drops of
the mixture enter
calcium chloride
solution, they form
‘beads’. The alginate
holds the enzyme
molecules in the beads.
Figure 3.15 Immobilising enzyme in alginate.
QUESTIONS
3.10 a Outline an investigation you could carry out to
compare the temperature at which the enzyme
lactase is completely denatured within 10
minutes
i when free in solution,
ii when immobilised in alginate beads.
b Outline an experiment you could carry out to
investigate how long it takes the enzyme lactase
to denature at 90 °C
i when free in solution,
ii when immobilised in alginate beads.
c Outline how you would determine the optimum pH
of the enzyme lactase
i when free in solution,
ii when immobilised in alginate beads.
3.11 Summarise the advantages of using immobilised
enzymes rather than enzyme solutions.