Download introduction to enzymes

Year 12 Biology Unit 1 – Enzymes
Name:
INTRODUCTION TO ENZYMES
1.
Enzymes are catalysts which catalyse specific reactions by lowering their activation energy.
The lock and key and the induced fit models have been used to explain the way in which
enzymes work.
(a)
Explain what is meant by activation energy.
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)
(i)
Describe how the lock and key model can be used to explain how an enzyme
breaks down a substrate molecule.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(ii)
Describe how the induced fit model differs from the lock and key model of
enzyme action.
...........................................................................................................................
...........................................................................................................................
(1)
Catalase is an enzyme found in many cells. It catalyses the breakdown of hydrogen peroxide as shown in the
equation.
hydrogen peroxide catalase

 water + oxygen
Cylinders of potato were cut with a cork
borer. The cylinders were then sliced
into discs of the same thickness and put
into a small beaker containing 50 cm3 of
hydrogen peroxide. The mass of the
beaker and its contents was recorded
over a period of 15 minutes. The results
are shown in the graph opposite
(c)
Explain why the mass of the
contents of the beaker fell as the
reaction progressed.
100
99
Mass of contents 98
of beaker as
percentage of
97
initial mass
96
.......................................................
........................................................
................…………………………
…………………………………....
95
0
5
10
Time/minutes
15
(1)
Year 12 Biology Unit 1 – Enzymes
(d)
Name:
Explain, in terms of collisions between enzyme and substrate molecules, why the rate of the reaction
changed over the period of time shown on the graph.
(2)
(Total 8 marks)
2.
The turnover number of an enzyme is defined as the number of substrate molecules converted to product by
one molecule of enzyme in one minute. In an experiment carried out at 20°C, the turnover number for an
enzyme was found to be 2500 at the start of the experiment but dropped to 1000 after 5 minutes.
(a)
(i)
Suggest why the turnover number decreased after 5 minutes.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
How would you expect the turnover number to differ from 2500 at the start of an identical
experiment but carried out at 30°C? Explain your answer.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(b)
Explain why it would be important to have a control in the experiment at 20°C and at 30°C.
.....................................................................................................................................
.....................................................................................................................................
(1)
(Total 5 marks)