Topic 2.5: Enzymes

Question 1

Definition of enzyme

Answer 1

A globular protein which acts as a biological catalyst by speeding up the rate of a chemical reaction

Question 2

Definition of active site

Answer 2

Region on an enzyme’s surface which binds to the substrate molecule

Question 3

Explanation of enzyme catalysis (4)

Answer 3

a) A substrate binds to the enzyme’s active site.
b) The enzyme catalyses the conversion of the substrate into product
c) The enzyme and product then dissociate
d) The enzyme can continue to catalyse further reactions

Question 4

Relationship between enzyme catalysis and collision frequency

Answer 4

The rate of enzyme catalysis can be increased by improving the frequency of collisions

Question 5

Effect of denaturation (pH / temperature) in enzyme activity

Answer 5

Any change to the tertiary structure of the active site (denaturation) will negatively affect the enzyme’s capacity to bind the substrate

Question 6

Specificity of active site to substrate (2)

Answer 6

a) The active site and the substrate complement each other in shape and chemical properties
b) Only a specific substrate is capable of binding to a particular enzyme’s active site

Question 7

Factors that affect the rate of activity of enzymes

Answer 7

a) pH
b) Temperature
c) Substrate concentration

Question 8

Effect of temperature on enzyme activity

Answer 8

a) Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in more collisions between the enzymes and substrates (higher enzyme activity).
b) At an optimal temperature, the rate of enzyme activity will be at its peak.
c) Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the enzyme’s hydrogen bonds

Question 9

Effect of pH on enzyme activity

Answer 9

a) Changing the pH will alter the charge of the enzyme, which in turn will alter protein solubility and overall shape
b) Changing the shape or charge of the active site will diminish its ability to bind the substrate, abrogating enzyme function
c) Enzymes have an optimal pH and moving outside this range diminishes enzyme activity

Question 10

Effect of substrate concentraton on enzyme activity

Answer 10

a) Increasing substrate concentration will increase the activity of a corresponding enzyme
b) More substrates mean there is an increased chance of enzyme and substrate colliding and reacting within a given period
c) After a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels

Question 11

Immobilised enzymes

Answer 11

Enzymes fixed to a static surface

Question 12

Benefits of immobilised enzymes

Answer 12

a) Localise reactions to particular sites
b) Conserved enzyme concentrations
c) Products more easily separated

Question 13

Uses of enzymes in industry

Answer 13

a) Biofuels
b) Biotechnology
c) Medicine
d) Food production

Question 14

Producing lactose-free milk

Answer 14

a) Lactase is purified from yeast or bacteria and then bound to an inert substance
b) Milk is repeatedly passed over immobilised lactase, becoming lactose-free

Question 15

Advantages of lactose-free dairy products

Answer 15

a) Product for lactose-intolerant individuals
b) Increasing sweetness in the absence of artificial sweeteners.
c) Reducing the crystallisation of ice-creams
d) Increasing bacteria fermentation / production of cheese and cottage cheese

Question 16

Definition of substrate

Answer 16

Substances that enzymes convert into products