2.1.4 Enzymes

Question 1

How do enzymes speed up the rate of reaction?

Answer 1

• Lower the activation energy
• Provide an alternative reaction pathway for the reactants

Question 2

True or false? Enzymes are used up during a chemical reaction.

Answer 2

FALSE - Enzymes are NOT used up during a chemical reaction.

Question 3

Which type of molecule is an enzyme?

Answer 3

A protein

Question 4

Name the process in the cells that produces enzymes.

Answer 4

Protein synthesis

Question 5

What does it mean if an enzyme is extracellular?

Answer 5

It functions outside of the cell

(But it is PRODUCED inside the cell)

Question 6

Name the enzyme that is involved in the decomposition of hydrogen peroxide.

Answer 6

Catalase

Question 7

What are the two products when hydrogen peroxide decomposes?

Answer 7

Oxygen and water

Question 8

Is catalase an intracellular or extracellular enzyme?

Answer 8

Intracellular

Question 9

Name the enzyme that breaks down starch into simple sugars.

Answer 9

Amylase

Question 10

Is amylase an example of an intracellular or extracellular enzyme?

Answer 10

Extracellular

Question 11

Name TWO places where amylase is produced.

Answer 11

Salivary glands and pancreas

Question 12

Name the part of the enzyme that is complementary in shape to the substrate.

Answer 12

Active site

Question 13

Describe ‘collision theory’ in terms of enzymes.

Answer 13

For enzymes to be able to catalyse a reaction, the enzyme and substrate must collide with:
- the correct speed
- the correct orientation

Question 14

Why can’t amylase catalyse the digestion of proteins?

Answer 14

Proteins are not complementary to the shape of the active site of amylase

Proteins cannot fit into amylase’s active site

Question 15

Describe how the ‘lock and key’ theory relates to enzymes.

Answer 15

• The substrate (key) fits into the active site like a lock
• The enzyme and substrate are complementary in shape (like a lock and key)
• The enzyme is specific to one substrate only (like a lock and key)

Question 16

Describe the induced fit hypothesis for enzymes.

Answer 16

The active site changes shape slightly when the substrate binds (conformational changes)

This is so the active site binds more closely to the substrate

Question 17

Name four factors that affect the rate of enzyme action.

Answer 17

• Temperature
• pH
• Enzyme concentration
• Substrate concentration

Question 18

What happens to an enzyme at extreme pH (either too high, or too low)?

Answer 18

It becomes denatured

Question 19

What does it mean when an enzyme becomes ‘denatured’?

Answer 19

Its active site changes shape

The substrate can no longer fit into the active site

Question 20

Why does a change in pH cause an enzyme to become denatured?

Answer 20

An excess of H+ or OH- ions can cause the hydrogen bonds and ionic bonds in the enzyme’s tertiary structure to break.

This alters the shape of the active site.

Question 21

True or false? At low temperatures, enzymes become denatured.

Answer 21

False

Question 22

Why is the rate of an enzyme-controlled reaction slow at low temperatures?

Answer 22

Enzyme and substrate have less kinetic energy

Enzyme and substrate move slowly

Less frequent successful collisions between enzyme and substrate

Question 23

Why are enzymes denatured at high temperatures?

Answer 23

The atoms in the enzyme have more kinetic energy

More vibrations inside the enzyme weakens hydrogen bonds

The active site changes shape

Question 24

What does Q10 stand for?

Answer 24

Temperature coefficient

Question 25

Q10 = R2 / R1

If R1 = 10 degrees Celsius, what is R2?

Answer 25

20 degrees Celsius

Question 26

Why does the rate of an enzyme-controlled reaction increase if the enzyme concentration remains constant, but the substrate concentration increases?

Answer 26

More frequent successful collisions (between active site and substrate)

More active sites are filled at a given time

Question 27

Explain why the rate of reaction plateaus, even when substrate concentration continues to increase.

Answer 27

All active sites are saturated (filled), so no more active-substrate complexes can form.

Question 28

What is a cofactor?

Answer 28

A non-protein substance bound to an enzyme that is needed for the enzyme to work.

Question 29

Name the substance that acts as a cofactor for amylase.

Answer 29

Chloride ions

Question 30

What is a prosthetic group?

Answer 30

A cofactor that is a permanent part of the enzyme’s structure

Question 31

Name the prosthetic group for carbonic anhydrase.

Answer 31

Zinc ions (Zn2+)

Question 32

Are inorganic cofactors changed during an enzyme-controlled reaction?

Answer 32

No

Question 33

Are coenzymes (organic cofactors) changed during an enzyme-controlled reaction?

Answer 33

Yes

Question 34

What is the function of a reversible inhibitor?

Answer 34

Temporarily reduces or stops an enzyme’s activity

Question 35

Where do competitive inhibitors bind?

Answer 35

To the enzyme’s active site

Question 36

How does a competitive inhibitor stop or reduce an enzyme’s activity?

Answer 36

Blocks the active site, so stops the substrate from binding

Question 37

Where do non-competitive inhibitors bind?

Answer 37

To an enzyme’s allosteric site

Question 38

How does a non-competitive inhibitor stop or reduce an enzyme’s activity?

Answer 38

• Binds to the allosteric site
• Which causes the active site to change shape
• Which stops the substrate from binding to the active site

Question 39

What process is shown in this diagram?

Answer 39

End product inhibition

Question 40

Describe what happens in end product inhibition.

Answer 40

The product of one enzyme-controlled reaction becomes the substrate for the next enzyme in the sequence

The end-product is used as a non-competitive, reversible inhibitor for the first enzyme in the sequence