1. Enzymes

Question 1

All enzymes are what type of proteins?

Answer 1

Globular

Question 2

What level of protein structure does the active site have?

Answer 2

Tertiary

Question 3

What do enzymes do to the activation energy of a reaction?

Answer 3

Lower it - this means the reaction can happen at lower temperatures

Question 4

All enzymes are ________ catalysts

Answer 4

Biological

Question 5

The 3D shape of an enzyme’s active site is…

Answer 5

Complementary to the shape of the substrate

Question 6

What happens in the enzyme-substrate complex?

Answer 6

Temporary bonds form between substrate and the amino acids that form the active site

Question 7

Describe the induced fit model of enzyme action

Answer 7

• enzyme is flexible

* substrate binds onto it: active site slightly changes shape, moulds around substrate

Question 8

What happens as the active site changes shape?

Answer 8

It puts strain on the substrate, distorting it and making the reaction more likely to happen

Question 9

What happens to the shape of the active site once the substrate leaves?

Answer 9

Goes back to its original shape

Question 10

Lactase balls milk practical: what are the advantages to this compared to adding the enzymes directly into a milk carton?

Answer 10

1. Can be reused/easy to reuse - in industry this saves resources
2. Slightly more temperature-stable so harder to denature

Question 11

Lactase balls milk practical: why were small beads used?

Answer 11

Large surface area for the milk to come into contact with the beads - more lactose can be broken down

Question 12

Lactase balls milk practical: what was the reason that the milk was tested for glucose?

Answer 12

To show that glucose is only present because it is a monomer of lactose (i.e. only present when lactose is broken down with lactase)

Question 13

Two definitions of rate of reaction

Answer 13

1. Measure speed at which substrate levels fall

2. Measure speed at which product levels rise

Question 14

4 factors that affect rate of enzyme-controlled reactions

Answer 14

1. temperature
2. pH
3. substrate concentration
4. enzyme concentration

Question 15

What determines optimum temperature?

Answer 15

The strength of the bonds that hold the tertiary structure together

Question 16

What is the optimum temperature for enzymes in the human body (and explain)?

Answer 16

Over 37°C - around 40

This allows some leeway for situations like having a hot drink, fever etc

Question 17

Is denaturation temporary or permanent?

Answer 17

Permanent!

Question 18

Explain temperature (x) against rate of enzyme activity (y) graph

Answer 18

1. temp increases → enzymes & substrates gain KE → more successful collisions → more enzyme-substrate complexes form
2. optimum temp: fastest rate of reaction
3. above optimum temp: enzyme denatured (tertiary structure disrupted so active site loses specific 3D shape). No longer complementary to substrate → e-s complexes can’t form

Question 19

What is pH a measure of?

Answer 19

hydrogen ion concentration

Question 20

Formula for pH

Answer 20

-logbase10[H+]

Question 21

Explain pH (x) against rate of enzyme activity (y) graph

Answer 21

1. optimum pH is when rate of reaction is fastest
2. as pH moves away from optimum, enzyme is denatured. Shape of active site disrupted → no longer complementary to substrate → e-s complexes won’t form

Question 22

How does changing the pH disrupt the active site?

Answer 22

Change in pH alters charge on the R group so disrupts tertiary structure (i.e. active site)

Question 23

Explain substrate concentration (x) against rate of reaction (y)

Answer 23

1. More enzymes than substrates: as substrate conc. increases, at any one time more active sites can be occupied. Substrate concentration is the limiting factor.
2. When number of enzymes = number of substrate molecules, reaction is at its fastest
3. More substrates has no effect on rate of reaction: at any one time all the active sites are occupied. Enzyme conc. is now the limiting factor

Question 24

Define limiting factor

Answer 24

The factor that is present in the least favourable amount and which therefore controls rate

Question 25

Explain enzyme concentration (x) against initial rate of reaction (y)

Answer 25

1. Enzyme conc is limiting factor: more substrate than enzyme. As enzyme conc increases there are more successful collisions and more E-S complexes form.
2. Same number of enzyme & substrate particles - all active sites are occupied. Rate of reaction is fastest here.
3. More enzymes than substrate molecules - substrate conc is now the limiting factor. Adding more enzymes doesn’t increase rate of reaction because all the substrate molecules are in an active site already.

Question 26

What is an inhibitor?

Answer 26

A substance that reduces the rate of an enzyme-controlled reaction by affecting the enzyme.

Question 27

What is a competitive inhibitor?

Answer 27

Similar shape to substrate
Doesn’t react with enzyme
Binds to active site to form an enzyme-inhibitor complex, blocking substrate’s access to active site

Question 28

Are competitive inhibitors usually permanently bound to the enzyme’s active site?

Answer 28

NO

Question 29

What is a non-competitive inhibitor?

Answer 29

Different shape to substrate
Binds to enzyme at the allosteric site (NOT active site!!)
Change the overall shape of the enzyme –> disrupts active site –> substrate can no longer bind to it (active site no longer complementary to substrate)

Question 30

Explain substrate conc (x) against initial rate of reaction (y) with non-competitive inhibitor

Answer 30

Non-competitive inhibitor binds to allosteric site, so reduces # of active sites that are complementary to the substrate. This reduces the chance of successful collisions between a substrate and active site, so fewer E-S complexes will form.

Plateaus at a lower level.

Question 31

Explain substrate conc (x) against initial rate of reaction (y) with competitive inhibitor

Answer 31

Competitive inhibitor and substrate compete for the active site. Increasing substrate concentration increases the chance that the active site will be filled with a substrate rather than an inhibitor.

Question 32

What is a metabolic pathway?

Answer 32

A series of linked chemical reactions each catalysed by its own enzyme

Question 33

Describe how the final product of the metabolic pathway can act as an inhibitor of the first step

Answer 33

The final product acts as a non-competitive inhibitor by binding to the allosteric site of the first enzyme, so preventing any more product from being produced.

Question 34

What is the advantage of this sort of end-point inhibition (i.e. when product acts as non-competitive inhibitor)?

Answer 34

Prevents waste

Question 35

4 marker: explain the effect of a competitive inhibitor on the rate of an enzyme-controlled reaction

Answer 35

1. binds to enzyme’s active site
2. similar shape to substrate
3. blocks substrate’s access & prevents the formation of enzyme-substrate complexes
4. rate decreases