Chapter 4: Enzymes

Question 1

Define ‘enzymes’.

Answer 1

They are proteins that function as biological catalysts.

Question 2

What do enzymes do?

Answer 2

They speed up the rate of chemical reactions by lowering activation energy.

Question 3

Why are enzymes required in a small amount in our body?

Answer 3

Enzymes remain chemically unchanged at the end of the reaction thus it can be reused.

Question 4

How do enzymes lower activation energy?

Answer 4

They provide an alternative pathway with lower activation energy required to start a chemical reaction.

Question 5

Why are enzymes needed?

Answer 5

Enzymes are needed to break down large molecules that cannot diffuse through the cell membrane into simpler and smaller substances so that they are soluble in water and are small enough to diffuse through the cell membrane.

Question 6

What can enzyme-catalysed reactions be classified into?

Answer 6

Anabolic and catabolic reactions

Question 7

What are anabolic reactions?

Answer 7

Reactions that build up complex substances.

Question 8

What are catabolic reactions?

Answer 8

Reactions that break down complex susbtances.

Question 9

Tell me about the specific nature of an enzyme using the lock-and-key hypothesis.

Answer 9

1. An enzyme has a specific three-dimensional shape and it has an active site.
2. Only the substrate complementary to that active site can fit into the enzyme. This results in the formation of an enzyme-substrate complex.
3. The enzyme is just like a lock and the substrate is just like a key. The substrate fits into the enzyme just like a key fits into a lock.
4. While the substrate is attached to the active site, a chemical reaction occurs. The substrate is converted to other products.
5. Later, the products leave the active site. The enzyme remains unchanged and it can catalyze another reaction.

Question 10

What are the characteristics of enzymes?

Answer 10

1. Enzyme speed up chemical reactions
2. Enzymes are specific in action
3. Enzymes are required in minute amounts and remain unchanged at the end of reactions
4. Enzymes are affected by temperature
5. Enzymes are affected by pH

Question 11

Describe how enzymes are affected by temperature.

Answer 11

1. Enzymes are less active at low temperatures as their KE is very low. Enzyme and substrate molecules move slowly, rate of effective collision is very low.
2. As temperature increases, KE of enzyme molecules also increases, leading to rate of effective collision increasing, increasing rate of enzyme-substrate complex formation.
3. Enzyme reaches maximum acitivity at its optimum temperature, 40 to 45 degress Celcius.
4. As temperature goes above enzymes’ optimum temperature, rate of enzyme reaction rapidly decreases as active site of molecules begin to lose original shape, no longer complimentary to shape of substrate molecules.
5. When temperature is very high above enzyme’s optimum temeprature, enzymes are denatured, substrate can no longer fit into enzyme’s active site to form enzyme-substrate complex.

Question 12

Define ‘denaturation’

Answer 12

It is the change in the three-dimensional structure of an enzyme or any other soluble protein that is caused by heat or chemicals.

Question 13

Describe how enzymes are affected by pH levels.

Answer 13

When enzymes are placed in pH conditions that vary from their optimum, they start to denature, thus substrate can no longer fit into enzyme’s active site to form enzyme-substrate complex.