Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
Answers to self-assessment questions
b
0.09
0.08
v / arbitrary units
0.07
0.06
0.05
0.04
0.03
½V max
= 0.059
0.02
0.01
K m
= 0.075
1
/ arbitrary units
0
0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
[S] / arbitrary units
40
35
30
25
20
15
–1 = –13.4
K m 10
1
∴ K 1
m
= = 0.118
13.4
v
5
0 5 10
c V max = 0.118 or 0.1
K m = 0.07 or 0.1
V max
1
[S]
= 8.5 ∴ V 1
max
= = 0.118
8.5
= 0 ∴ [S] = ∞
⎫
⎬
⎭
V max
at infinite [S] = 0.118
15 20 25 30 35 40 45 50
1
/ arbitrary units
[S]
9 Lysozyme, because it has the lowest K m .
(Carbonic anhydrase has the highest V max .)
10a Prepare a solution of lactase and a separate
sample of lactase immobilised in alginate
beads. Suspend the beads in water. Heat
separate samples of lactase in solution and
immobilised lactase beads suspended in
water at a range of temperatures (e.g. 40 °C to
100 °C) for 10 minutes each. Allow to cool to
room temperature.
If the enzyme is still active, it will catalyse
the hydrolysis of lactose to glucose and
galactose: 1 mole of lactose will produce 1
mole of glucose and 1 mole of galactose. All
are reducing sugars, but the concentration of
reducing sugar will double as a result of the
reaction. A semi-quantitative Benedict’s test
on a sample before and after the reaction can
therefore be used to find out if the enzyme
is active. This can be done by mixing the
enzyme with lactose (or milk) at a suitable
temperature (e.g. 37 °C), and leaving for a few
minutes. In the case of the lactase beads, the
beads would first have to be tipped into a
sieve to remove the surrounding water before
being added to a solution of lactose.
b Suspend the lactase beads in water. Leave
samples of the enzyme solution and the
immobilised lactase beads for different
lengths of time at 90 °C. Then test for enzyme
activity as in a above.
c Prepare a series of lactase solutions of
different pH using appropriate buffer
solutions. For each pH, use some of the
solution to make alginate beads containing
immobilised enzyme. Then carry out the
reaction using milk or lactose as a substrate
and test for enzyme activity as in a above.
11 Immobilised enzymes do not contaminate
the product. They are not lost, so they can
be re-used. They are able to work at a wider
range of pH than enzymes in free solution,
and also a wider range of temperature.
Cambridge International AS and A Level Biology © Cambridge University Press 2014