Role of
Enzymes
Unit 1
Sub-topic 2
Cell Function and Inheritance
Enzymes
Enzymes are one product of protein synthesis. They are described as globular proteins
with catalytic properties. They are essential in biological systems where hundreds of
biochemical reactions are taking place in a controlled manner and at relatively low
temperatures. They do not cause reactions to occur; they only speed up ones that
normally happen at a very slow rate.
1 a) Explain fully why an enzyme described as a biological catalyst, and what
would happen without them?
b) What is the difference between an intracellular and an extracellular enzyme?
c) What determines the shape of an enzyme’s active site?
d) Explain why an enzyme is said to be specific in its relationship with its substrate.
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f) Draw a labeled diagram for each of the two biochemical reactions enzymes
promote.
………………………… reaction
…………………………. reaction
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Factors affecting enzyme activity
Enzymes require particular conditions in which to function efficiently.
1 a) List the factors that you know affect enzyme activity.
b) Increases in temperature initially cause enzyme activity to increase as this
increases kinetic energy which results in more collisions between the enzyme and
its substrate.
(i) What happens after 40 oC? Explain why?
increasing rate of reaction
(ii) Label the graph at points A, B and C to show the effect of temperature at each.
B
C
A
temperature oC
c) What does optimum mean
d) (i) Which pH do most enzymes work best at?
(ii) Name 2 exceptions.
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(iii) What happens if an enzyme is exposed to the wrong pH?
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Effects of concentrations of enzymes and substrates
2 a) (i) In general, what effect does an increase in concentration of an enzyme have on
reaction rate when the substrate is present in excess? Explain why.
(ii) What effect does an increase in concentration have on reaction rate when a
limited concentration of substrate is present? Explain why.
(iii) Complete the summary diagram to show the effect of increasing enzyme
concentration on rate of reaction.
b) (i) What effect does an increase in concentration of substrate have on reaction
rate when the enzyme is present in excess? Explain why.
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(ii) What effect does an increase in concentration of substrate have on reaction
rate when a limited concentration of enzyme is present? Explain why.
Practical: The effect of enzyme concentration on enzyme action
Enzyme Inhibitors
Enzyme activity can also be affected by other substances called inhibitors.
1 a)(i) Define the term inhibitor with respect to enzymes.
(ii) Name the 2 types of inhibitors.
b)(i) What property of a competitive inhibitor enables it to compete with the
substrate?
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(ii) Explain how competitive inhibitors reduce the rate of a reaction?
(iii) Draw a diagram to illustrate the actions of a competitive inhibitor.
(iv) What effect does an increase in concentration of competitive inhibitor have on
reaction rate when the concentration of substrate present is limited?
Explain why.
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c) Describe how a non-competitive inhibitor acts on an enzyme.
d) Explain why increasing the concentration of substrate increases the rate of
reaction when a competitive inhibitor is present, but has little effect when a noncompetitive inhibitor is present.
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Activation of enzymes
Many enzymes require the presence of other, non-protein substances in order to become
activated. These substances are called co-factors.
Other enzymes need to be activated by another enzyme called an enzyme activator.
Co-factors
1 a)(i) Briefly describe how most co-factors are thought to play their role.
(ii) Name some mineral ions that are important enzyme activators.
(iii) What other substances act as co-factors and where do many of these come from?
(iv) Label the diagram and briefly note what is happening underneath each stage in this
co-factor / enzyme reaction.
1
2
3
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b) Despite being essential ingredients in the diet vitamins are only required in tiny
quantities. Explain why.
Enzyme activators
c) (i) Name the enzyme activators that convert trypsinogen and chymotrypsinogen into
their active forms.

trypsinogen

chymotrypsinogen
(ii) Why is it important that these two digestive enzymes remain inactive until they
contact this enzyme activator.
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Inborn errors of metabolism
Occasionally faults occur in the genetic information to produce a particular enzyme
resulting in that enzyme not functioning correctly or being completely absent.
1 a) Define the term metabolism.
b) By what type of substance is each stage in a metabolic reaction controlled?
c) (i) What causes an inborn error of metabolism?
(ii) What effect can the absence of an enzyme have on a metabolic pathway?
(iii) Describe the effect of a faulty gene for the production of enzyme Y in this
metabolic pathway.
enzyme X
substance P
enzyme Y
substance Q
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substance R
d) (i)Describe the cause and effect of the disorder phenylketonuria (PKU).
(ii) Describe how albinism arises.
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