Enzymes

Question 1

What are immobilised enzymes?

Answer 1

Enzymes that are fixed to an inert matrix over which the substrate molecules move.

Question 2

State the two main ways enzyme immobilisation can be achieved.

Answer 2

1) Entrapment- held inside a gel, e.g. silica gel

2) Micro-encapsulation- trapped inside a micro-capsule, e.g. alginate beads

Question 3

Define metabolism

Answer 3

The sum of all the enzyme controlled chemical reactions taking place

Question 4

State the two main types of reactions that make up metabolism.

Answer 4

Anabolic and catabolic reactions

Question 5

What is anabolism?

Answer 5

A set of metabolic pathways that synthesise complex molecules from smaller, simpler molecules.

Question 6

What is catabolism?

Answer 6

A set of metabolic pathways that breakdown complex molecules into smaller, simpler molecules.

Question 7

What is an enzyme?

Answer 7

• A biological catalyst used to speed up the rate of intracellular and extracellular biochemical reactions

• Not used up or permanently altered

Question 8

What is an intracellular enzyme?

Answer 8

An enzyme that acts within cells, e.g. catalase.

Question 9

What is an extracellular enzyme?

Answer 9

An enzyme is secreted by cells and functions outside of cells, e.g. amylase.

Question 10

What is the active site of an enzyme?

Answer 10

A region on an enzyme that is complementary to the shape of a specific substrate. The substrate binds and the reaction takes place.

Question 11

Why is an active site described as ‘specific’?

Answer 11

• The 3D structure of each enzyme (including the active site) is unique due to the presence of different side chains and branches

• Only specific substrates complementary to the active site can bind

Question 12

Define activation energy

Answer 12

The minimum amount of energy required for a reaction to take place.

Question 13

What is catalysis?

Answer 13

• An increase in the rate of a chemical reaction using a catalyst (such as an enzyme)

• The catalyst lowers the activation energy of the reaction

Question 14

Describe the ‘lock and key’ model.

Answer 14

1) Substrate(s) and the active site of the enzyme come into contact

2) Substrate(s) binds, enzyme-substrate complex forms

3) Reaction takes place, product(s) formed in an enzyme-product complex

4) Product(s) released from the active site. The active site is now free to bind to another substrate

Question 15

What is the induced fit hypothesis?

Answer 15

A model of enzyme action which states that once a specific substrate binds to the active site, the enzyme undergoes subtle conformational changes. This puts a strain on the substrate, lowering the activation energy for the reaction.

Question 16

What factors affect the rate of an enzyme-controlled reaction?

Answer 16

• Temperature
• pH
• Substrate concentration
• Enzyme concentration

Question 17

Explain how increasing temperature above the optimum affects the rate of an enzyme-controlled reaction.

Answer 17

• Temperature increases above the optimum

• Increased vibrations break hydrogen and ionic bonds in tertiary structure

• Active site changes shape, enzyme is denatured

• No more enzyme-substrate complexes can form

• Rate of reaction decreases

Question 18

How does temperature effect the rate of enzyme-controlled reactions?

Answer 18

• As temperature increases molecules have more KE

• Molecules move faster and collide more frequently

• More enzyme-substrate complexes form

• Rate of reaction increases

• Rate peaks at the optimum temperature

Question 19

How does pH affect the rate of enzyme-controlled reactions?

Answer 19

• Enzymes have an optimum pH

• pH shifts from the optimum

• Hydrogen and ionic bonds in the tertiary structure are altered

• Interaction of polar and charged R-groups changes

• Active site changes shape, enzyme is denatured

• Rate of reaction decreases

Question 20

What is a buffer?

Answer 20

A molecule that maintains a constant pH in a solution when small volumes of acid (H+) or base (OH-) are added.

Question 21

How does substrate concentration affect the rate of an enzyme-controlled reaction?

Answer 21

If an enzyme concentration is fixed, the rate of reaction increases proportionally to the substrate concentration.

Once all active sites become full, the rate of reaction remains constant (graph plateaus)
Enzyme concentration is a limiting factor

Question 22

How does substrate concentration affect the rate of an enzyme-controlled reaction?

Answer 22

If an enzyme concentration is fixed, the rate of reaction increases proportionally to the substrate concentration.

Once all active sites become full, the rate of reaction remains constant (graph plateaus)
Enzyme concentration is a limiting factor

Question 23

How does enzyme concentration affect the rate of an enzyme-controlled reaction?

Answer 23

If substrate concentration is fixed, the rate of reaction increases proportionally to the enzyme concentration.

When all of the substrate occupy active sites, the rate of reaction plateaus
(substrate concentration is a limiting factor)

Question 24

How does enzyme concentration affect the rate of an enzyme-controlled reaction?

Answer 24

If substrate concentration is fixed, the rate of reaction increases proportionally to the enzyme concentration.

When all of the substrate occupy active sites, the rate of reaction plateaus
(substrate concentration is a limiting factor)

Question 25

What is a competitive inhibitor?

Answer 25

A molecule which competed for the active site of an enzyme, blocking it and preventing the substrate from binding.

Question 26

Is competitive inhibition temporary or permanent?

Answer 26

Competitive inhibition is generally temporary. However, in some cases (e.g. aspirin) it may be permanent.

Question 27

How does increasing substrate concentration affect competitive inhibition?

Answer 27

• Increase in substrate concentration

• More substrate than inhibitor

• Rate of reaction increases

Question 28

What is a non-competitive inhibitor?

Answer 28

• An inhibitor which binds to a different part of an enzyme, the allosteric site

• The tertiary structure of the enzyme (including the active site) changes shape

• The active site is no longer complementary to the substrate. The substrate cannot bind and the enzyme is inhibited

Question 29

Is non-competitive inhibition temporary or permanent?

Answer 29

Permanent

Question 30

How does increasing the substrate concentration affect non-competitive inhibition?

Answer 30

Increasing the substrate concentration will not overcome the effect of the non competitive inhibitor.

Question 31

What are immobilised enzymes?

Answer 31

Enzymes which are attached to an inert insoluble material over which the substrate passes and the reaction takes place.

Question 32

Give an example of an application of immobilised enzymes.

Answer 32

Biosensors

Question 33

Why are immobilised enzymes important in industrial processes?

Answer 33

• Enables enzymes to be reused

• Improves enzyme stability in variable/extreme temperatures and pH

• Increases the efficiency of reactions

Question 34

State the two main inert matrix examples.

Answer 34

1) Sodium alginate beads
2) Cellulose microfibrils

Question 35

Compare the volume to surface area ratio of large beads to smaller beads.

Answer 35

If a given material is used to make large beads, there will be a smaller total surface area, than for smaller beads.

If smaller beads are made, the substrate molecule will have easier access to enzyme molecules, producing a higher rate of reaction.

Question 36

Advantages of immobilising enzymes with a polymer matrix?

Answer 36

• Makes them more stable- it creates a microenvironment allowing reactions to occur at higher temps/more extreme pHs than normal

• Trapping an enzyme molecule prevents the shape change (which denatures AS) so the enzyme can be used in a wide range of physical conditions (compared to if it was free in solution)

Question 37

Why do enzymes immobilised in beads have a lower rate of reaction than those enzymes immobilised on a membrane? (if all other factors are constant)

Answer 37

Some of the active sites are inside the beads, and the substrate takes time to diffuse to them.

Enzymes on a membrane are readily available for binding (-> higher reaction rate)

Question 38

State what is meant by an isomer

Answer 38

Same chemical formula but a different structural formulae.