4 | Enzymes

Question 1

Define enzymes

Answer 1

Enzymes are biological catalysts made up of proteins. They lower down the activation energy for a reaction to occur, alter or speed up the rate of chemical reactions without themselves being chemically changed at the end of the reaction.

Question 2

What is activation energy?

Answer 2

Activation energy is the energy needed to start a chemical reaction

Question 3

Characteristics of enzymes?

Answer 3

• Three dimensional shape held by weak hydrogen bonds
• Can catalyse reversible reactions
• Affected by temperature and pH
• Speed up rate of chemical reaction (lowering activation energy)
• Made up of proteins
• Specific in nature
  –lock and key hypothesis
• Remains unchanged at the end of the reaction
  – Can be used again and again
  – Only a small amount is required for a large amount of substrate.

Question 4

What are the factors affecting the rate of enzyme reactions

Answer 4

SEPT
Substrate concentration
Enzyme concentration
pH
Temperature

Question 5

How does substrate concentration affect the rate of enzyme reactions?

Answer 5

If more substrate is available, the rate increases.
But enzyme rate has a limit
- plateau

Question 6

How does enzyme concentration affect the rate of enzyme reactions?

Answer 6

more enzymes → more reactions per unit → rate increases

Question 7

How does pH affect the rate of enzyme reactions?

Answer 7

• Extreme changes in pH denatures the enzyme.
• Different enzymes have different optimum pH

Question 8

What happens to enzymes below/above optimum pH?

Answer 8

• weak hydrogen bonds in three-dimensional enzyme structure is broken.
• the 3D shape of the enzyme is lost and the shape of the active site is altered.
• Substrate can no longer bind to the active site of the enzyme and no enzyme-substrate complexes are formed.
• Enzyme is denatured and rate of reaction decreases to zero

Question 9

What happens to enzymes at optimum pH?

Answer 9

• Enzyme is most active
• Rate of formation of enzyme substrate complex is at its maximum and rate of reaction is the highest

Question 10

What happens during denaturation?

Answer 10

• During denaturation, hydrogen bonds are broken, thus there will be a loss of 3D structure and loss of active site. Substrate no longer binds to active site of enzyme. Therefore, no enzyme-substrate complex is formed, no chemical reactions and thus no products formed.
• When an enzyme is denatured, the shape of the active site is changed, and no longer complementary to the 3D shape of the substrate

Question 11

When does denaturation occur?

Answer 11

• High temp (beyond optimum)
• Extreme pH changes

Question 12

What is the lock and key hypothesis?

Answer 12

Enzyme is the lock and substrate is the key.
Substrate has a 3D shape complementary to the active site of the enzyme (active sites on enzymes have a specific shape that can only bind with a specific substrate)
Enzyme and substrate bind to form enzyme-substrate complex.
The enzyme remains chemically unchanged at the end of the reaction.

Question 13

Ans structure of lock and key hypothesis?

Answer 13

1. Enzyme is the lock, substrate is the key
2. Substrate has a 3D shape that is complementary to the active site on the enzyme
3. Substrate binds to enzyme to form an lock-key complex / substrate is able to fit and bind to the active site to form the enzyme-substrate complex.
4. Substrate is digested into product.