Chapter 4 : Enzymes

Question 1

State the 7 characteristics of enzymes

Answer 1

1. Speed up chemical reaction
2. Required in minute amounts
3. Highly specific in action
4. Affected by temp
5. Affected by pH
6. Some catalyse reversible reactions
7. Some require coenzymes for activity

Question 2

How do enzymes speed up chemical reactions ?

Answer 2

They lower the activation energy required for the reaction by providing an alternative pathway with a lower activation energy

Question 3

State the real life applications of these 3 enzymes
1. Protease
2. Pectinase
3. Lactase

Answer 3

1. Found in bio-active detergent to remove protein stains
2. Speed up extraction of fruit juice from fruit by breaking down pectin
3. Help to break down lactose for lactose free milk

Question 4

Explain what is proposed by the Lock-and-key hypothesis (3)

Answer 4

1. Enzyme has a particular shape which fits the substrates exactly
2. The substrate which has the specific shape binds to the active site of the enzyme
3. Once formed, the products no longer fit into the active site and escape into the surroundings, leaving the enzyme free to catalyse more reactions

Question 5

What is proposed by the induced fit hypothesis ?

Answer 5

1. Active site does not begin with exact shape complementary to that of substrate.
2. Rather, it is the binding of the substrate to the active site of the enzyme which induces a small conformational change in the shape of the enzyme
3. Substrate fits more tightly into active site and enzymes are able to perform catalytic reactions more effectively

Question 6

What does it mean when a protein denatures? Why can enzymes no longer catalyse reactions once denatured

Answer 6

The protein denatures when it unfolds and loses its 3d shape. Precise shape of the active site is lost, the destruction is irreversible

Question 7

Explain the relationship between temperature and enzyme (4)

Answer 7

As the temperature incr. , the KE of substrate and enzyme molecules incr.
No. of Effective collisions between substrate and enzyme incr —> rate of reaction then increases
This occurs until the optimum temperature, anything beyond the optimum temperature causes the rate of reaction to decrease rapidly.
This is because the enzyme denatures and loses its 3d shape

Question 8

Explain the relationship between pH and enzyme activity

Answer 8

The optimum pH is where the intermolecular bonds which maintain the conformation of the enzymes are intact, making it the most ideal for substrate bonding. The frequency of successful collisions between enzyme and substrate is the highest.

At other pH levels, the ionic charges on the basic and acidic groups on the side chains of the amino acid residues on the enzyme would be altered. Ionic bonding that helps to maintain the conformation of the enzyme would be disrupted, affecting the active site for substrate binding.

This conformational change is reversible within a certain change. However, it the change is too drastic, conformation of the ste is severely altered and the protein is denatured.

Question 9

Factors affecting enzyme function

Answer 9

1. Enzyme concentration
2. Substrate conc
3. Temperature
4. PH
5. Salinity
6. Activators
7. Inhibitors

Question 10

Difference between reversible and irreversible inhibition

Answer 10

In a reversible inhibition, the inhibitor can leave the enzyme and the enzyme can return to catalysing reaction

In an irreversible inhibition, the inhibitor is permanently bound and the enzyme is permanently inhibited. Enzyme can no longer catalyse reaction.

Question 11

What’s the difference between competitive and non-competitive inhibition (3)

Answer 11

Competitive inhibitors bind to the active site of the enzyme while non-competitive inhibitors bind to a region other than the active site. This causes conformational change in the active site of the enzyme

Competitive inhibitors have structural resemblance to substrate while non-competitive inhibitors do not share structural resemblance

While competitive inhibition can be countered by increasing substrate concentration, non competitive inhibition cannot be countered the same way. Max rate of reaction for non-competitive inhibition would be lower