Module 2 - Enzymes

Question 1

What are enzymes?

Answer 1

• globular proteins which reduce the activation energy of a chemical reaction by binding to a substrate

Question 2

How does the structure of an enzyme relate to its function?

Answer 2

• it contains an active site that binds to a specific substrate

Question 3

How do enzymes work?

Answer 3

• they bind to a specific substrate molecule and bring them into proximity with each other
• this allows the substrate molecule to react more readily and increases the likelihood of a successful reaction.

Question 4

What are the two main models that explain enzyme and substrate binding?

Answer 4

• lock and key model
• induced fit model

Question 5

Explain the lock and key model

Answer 5

• the shape of the active site is always complementary to the shape of the substrate

Question 6

Explain the induced fit model

Answer 6

• substrate binds to the enzyme’s active site.
• as substrate binds, the shape of the active site changes slightly.
• reaction takes place and enzyme-product complex is formed
• products are then released from the active site

Question 7

What are the three types of molecules which help in enzymatic reactions?

Answer 7

• cofactors
• coenzymes
• prosthetic groups

Question 8

What are cofactors?

Answer 8

• non-protein molecules
• inorganic molecules or ions

Question 9

What is the role of cofactors?

Answer 9

• help bind the substrate and enzyme.
• not used up directly in the reaction itself

Question 10

What are coenzymes?

Answer 10

• organic molecules e.g vitamins

Question 11

What is the role of coenzymes?

Answer 11

• help transfer chemical groups between different enzymes
• they move between different enzymes and get changed during the reaction but are not used up

Question 12

What are prosthetic groups?

Answer 12

• cofactors that are permanently bound to the enzyme itself
• part of the active site itself

Question 13

What are the two types of inhibitors?

Answer 13

• competitive and non-competitive

Question 14

What are inhibitors?

Answer 14

• substances that bind to the active site of the enzyme and prevent it from binding to the substrate.
• this reduces or stops the activity of the enzyme

Question 15

Why are enzymes sensitive to changes in the environment?

Answer 15

• they are proteins
• have tertiary structures that require optimal conditions to keep functioning

Question 16

How does the temperature change the enzyme’s rate of reaction?

Answer 16

• as temp increases, so does the KE of reactants.
• this increases the frequency of successful collisions resulting in a reaction between the enzyme and substrate

Question 17

What occurs at very high and very low temperatures?

Answer 17

• denaturation
• bonds in the active site begin to break and the tertiary structure is disrupted.
• this alters the specific shape of the active site so it is no longer complementary to the substrate

Question 18

How does the pH change the enzyme’s rate of reaction?

Answer 18

• enzymes denature at extremes of pH
• hydrogen and ionic bonds holding the tertiary structure of the protein together may break
• this alters the shape of the active site which means enzyme-substrate complexes form less easily

Question 19

How does the enzyme concentration affect the rate of reaction?

Answer 19

• the higher the enzyme concentration in a reaction mixture, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation
• as long as there is sufficient substrate available, the initial ror increases linearly with enzyme concentration
• if the amount of substrate becomes a limiting factor, there is no further increase in enzyme concentration.

Question 20

How does the substrate concentration affect the rate of reaction?

Answer 20

• the greater the substrate concentration, the higher the rate of reaction
• as num of substrates increases, the likelihood of enzyme-substrate complexes forming increases
• If the enzyme concentration remains fixed but the amount of substrate is increased, all available active sites eventually become saturated .
• When the active sites of the enzymes are all full, there are no possible enzyme-substrate complexes to be formed

Question 21

What are competitive inhibitors?

Answer 21

• have a similar shape to substrate molecules and therefore compete for the active site with the substrates.

Question 22

What are non-competitive inhibitors?

Answer 22

• inhibitors that bind to the enzyme at an alternative site, altering the shape of the active site and therefore preventing the substrate from binding to it.

Question 23

What effect do reversible inhibitors have on the rate of reaction?

Answer 23

• slow down enzymes therefore decreasing the rate of reaction

Question 24

How is it possible to counter the increase of competitive inhibitors?

Answer 24

• increasing the substrate concentration
• more substrate molecules, more likely to collide with enzymes and form enzyme-substrate complexes

Question 25

Why cannot non-competitive inhibition be overcome by increasing the substrate concentration?

Answer 25

• they don’t compete for the active site, instead, they change the site of the active site, meaning no matter how many substrates there are, they will not be able to fit in the active site

Question 26

Reversible inhibitors are used as regulators in what?

Answer 26

• regulators in metabolic reactions

Question 27

How can metabolic reactions be controlled?

Answer 27

• using a non-competitive inhibitor in end-product inhibition
• as the enzyme converts the substrate into a product, the process is slowed down as the end-product of the reaction binds to an alternative site on the original enzyme, changing the shape of the active site and preventing the formation of further enzyme-substrate complexes
• the end-product then detaches from the enzyme and is used elsewhere, allowing the active site to reform and the enzyme to return to an active state
• this means that as product levels fall, the enzyme begins catalysing the reaction once again, in a continuous feedback loop