Factors Affecting Enzyme Activity (Page 3 of 3) in pdf

Factors Affecting Enzyme Activity

However, if the concentration of the normal substrate is increased, reversible

Practice Questions

inhibitors are displaced from the active site and the normal enzyme substrate

complex can form (Fig 7).

1. Define the following terms:

Fig 7.

Effect of increased substrate concentration on

(a) induced fit hypothesis

(3 marks)

reversible competitive inhibition

(b) denaturation

(3 marks)

2. The graph show the effect of increasing substrate concentration on

the rate of an enzyme controlled reaction.

inhibitor

Competitive

inhibitor

Substrate concentration

Example 1: arabinose competes with glucose for the active sites on

glucose oxidase.

Substrate concentration

Example 2: oxaloacetate, malonate and pyrophosphate all compete with

succinate for the active site of the enzyme succinate dehydrogenase.

(a) Explain the shape of the curve between points x and y (2 marks)

Example 3: an individual who swallows methanol is in danger of

becoming blind. This is because the methanol – which itself is not toxic

(b) Describe and explain the effect which a competitive reversible

– will be metabolised to formaldehyde which is extremely toxic and

inhibitor would have on the rate of this reaction

will cause blindness. At hospital, the individual will be treated with

(2 marks)

ethanol. The ethanol is structurally similar to methanol and will compete

with methanol for the enzyme’s active sites. Thus, the metabolism of

Answers

methanol is slowed down.

Semicolons indicate marking points

Non-competitive reversible inhibitors react with the enzyme but not at

1. (a) substrate approaches active site;

the active site. They change the shape of the whole enzyme, including the

causes shape of active site to change;

shape of the active site, hence the reaction cannot proceed and no products

allows formation of enzyme/substrate complex;

are formed on those enzymes (Fig 8).

products do not fit active site therefore diffuse away;

Fig 8. Effect of increased substrate concentration on non-

(b) loss of quaternary/tertiary structure;

competitive inhibition

loss of active site/permanent change in shape of active site;

enzyme-substrate complex unable to form;

caused by above optimum temperatures/pH above or below

optimum;

2. (a) substrate concentration is limiting factor;

as concentration increases more enzyme substrate complexes

inhibitor

form;

(b) slow it down;

Non-competitive

inhibitor

competitive inhibitor will occupy active sites;

reducing number of enzyme-substrate complexes;

Substrate concentration

(b) Irreversible inhibitors

Irreversible inhibitors bind covalently and permanently to the enzyme,

Acknowledgements;

This Factsheet was researched and written by Kevin Byrne

preventing normal enzyme function. For example, Aspirin is an

Curriculum Press, Unit 305B, The Big Peg, 120 Vyse Street, Birmingham. B18 6NF

irreversible inhibitor of cycloxygenase, an enzyme involved in the

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synthesis of prostaglandins. Substances such as mercury, iron and

school is a registered subscriber.

arsenic bind irreversibly to the SH (sulphydryl) group on enzymes.

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ISSN 1351-5136

Factors Affecting Enzyme Activity Page 3

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