2: Enzymes

Question 1

What do catalysts do?

Answer 1

• speed up chemical reactions without being changed themselves

Question 2

Define ‘enzyme’.

Answer 2

• biological catalysts produced by living organisms that speed up and control the rate of reactions of metabolism
• globular proteins

Question 3

Define ‘substrate’.

Answer 3

a reactant in an enzyme-catalysed reaction

Question 4

What makes it possible for enzymes to catalyse reactions?

Answer 4

• special region called the active site

catalysis only occurs if the substrates are in a liquid:
- molecules are in continual random motion
= chance of collusions between the substrates and the active site on the surface of the enzyme

Question 5

What do collisions between active site and substrate result in? Why?

Answer 5

binding
- the shape and chemical properties of the active site complement those of substrates
= they are chemically attracted to each other and fit together

Question 6

State and define a key characteristic of enzymes.

Answer 6

enzymes are “substrate specific”

= molecules other than the substrate do not fit or are not attracted so do not bind

Question 7

How do enzymes speed up metabolic reactions?

Answer 7

• binding of substrates to the active site reduces the energy needed for them to be converted into products

Question 8

What happens to the substrate once it binds to the active site of an enzyme?

Answer 8

• substrate converted into products

- products released, freeing it up to catalyse reactions with more substrates

Question 9

How fast can an enzyme catalyse its reaction?

Answer 9

many times a second

Question 10

Where else, outside living organisms, are enzymes widely used? What for?

Answer 10

in industry for catalysing specific reactions

Question 11

What type of enzymes are the enzymes used in industry?

Answer 11

immobilized enzymes - enzymes attached to another material or into aggregations (groups) to restrict their movement

Question 12

State 5 benefits of using immobilised enzymes in industry.

Answer 12

1. catalysis can be controlled by adding/ removing enzymes promptly from reaction mixture
2. enzyme concentrations can be higher
3. enzymes can be reused, saving money
4. enzymes are resistant to denaturation over greater ranges of pH and temperature
5. products are not contaminated with enzymes

Question 13

Name some methods of immobilising enzymes.

Answer 13

1. attachment to surfaces such as glass (absorption)
2. entrapment in a membrane or a gel (e.g. alginate)
3. aggregation by bonding enzymes together into particles of up to 0.1mm diameter

Question 14

What molecule is the sugar in milk?

Answer 14

lactose

Question 15

What does lactase do to lactose?

Answer 15

lactase hydrolyses lactose into: glucose + galactose

Question 16

How is lactose-free milk produced?

Answer 16

• either by adding free lactase to milk

- or by using lactase that has been immobilised on a surface or in beads of a porous material

Question 17

Draw a diagram of ‘making alignate beads containing lactase’. (p26)

Answer 17

1. syring
2. mixture of sodium alignate and lactase
3. 2% calcium chloride solution
4. bead

Question 18

Draw a diagram of ‘adding lactase that has been immobilised on a surface or in beads of porous material’ (p26)

Answer 18

1. aliginate beads containing lactase
2. syringe barrel
3. screw gate clip
4. glucose test strip

Question 19

How is lactase obtained?

Answer 19

from microorganisms such as Kluveromyces lactis, a yeast that grows in milk

Question 20

Name some advantages of lactose-free milk.

Answer 20

1. many people are lactose intolerant and cannot drink more than 250ml of milk per day unless it is lactose-reduced
2. galactose and glucose = sweeter than lactose, so less sugar needs to be added to sweet foods containing milk, such as milk shakes or fruit yoghurt
3. lactose tends to crystallize during production of ice cream, giving it a gritty texture. Because glucose and galactose are more soluble than lactose they remain dissolved, giving a smoother texture
4. bacteria ferment glucose and galactose more quickly than lactose, so the production of yoghurt and cottage cheese is faster