Enzymes

Question 1

What are the rates of chemical reactions that occur in living cells controlled by?

Answer 1

The rate of these reactions are controlled by a special group of proteins called enzymes.

Question 2

What is the definition of enzymes?

Answer 2

Enzymes are biological catalysts, made by all living cells. They speed up cellular reactions and are unchanged in the process.

Question 3

Why are enzymes known as “biological catalysts?

Answer 3

Enzymes are known as “biological catalysts” because they are chemicals that are made by living cells. Without enzymes, chemical reactions would be too slow to sustain life.

Question 4

What are the two types of enzyme-controlled chemical reactions?

Answer 4

1) Degradation reactions

2) Synthesis reactions

Question 5

What is the definition of degradation reactions?

Answer 5

Large complex molecules are broken down into smaller simpler ones.

Question 6

What is the definition of synthesis reactions?

Answer 6

Small, simple molecules are built into large complex ones.

Question 7

Give an example of a degradation reaction.

Answer 7

For example, digestion reactions: starch being broken into maltose and then glucose.

Question 8

Give an example of a synthesis reaction.

Answer 8

For example, glucose (made during plant photosynthesis) being built up into starch.

Question 9

Explain what happens when an enzyme-controlled reaction takes place.

Answer 9

During an enzyme-controlled reaction the molecule on which an enzyme works, called the substrate, joins temporarily at the active site on the surface of the enzyme. This facilitates the chemical reaction which can now take place quickly and forms the product or products.

Question 10

What is the definition of a substrate?

Answer 10

The molecule the enzyme is working on.

Question 11

What is the definition of a product?

Answer 11

Molecule produced at the end of the reaction.

Question 12

Why are enzymes said to be specific to a particular substrate?

Answer 12

Enzymes are said to be specific to a particular substrate because the shape of the active site of an enzyme molecule is complementary to its specific substrate(usually one type of substrate).

Question 13

How can we identify starch?

Answer 13

Starch can be identified by using iodine solution.

Question 14

What colour is iodine when starch is absent?

Answer 14

If starch is absent iodine is brown.

Question 15

What colour is the iodine if starch is present?

Answer 15

If starch is present iodine is black/blue.

Question 16

Name the substrate, enzyme and products present in the degradation reaction(catalase and hydrogen peroxide) and how we can measure the rate of reaction.

Answer 16

Substrate: hydrogen peroxide
Enzyme: catalase
Products: oxygen and water

The rate of reaction can be measured by:

Capturing the oxygen in a measuring cylinder and measuring its volume over a period of time

Using detergent to capture the oxygen and measure the height of foam produced over a period of time.

Question 17

Name the substrate, enzyme, and product produced in the synthesis reaction (making starch) and how we can identify starch.

Answer 17

Substrate: glucose-1-phosphate
Enzyme: phosphorylase
Product: starch

We can identify starch by using iodine solution.

Question 18

When are enzymes most active?

Answer 18

Each enzyme is most active in its optimum conditions.

Question 19

What are the two factors affecting enzyme activity?

Answer 19

Enzymes are affected by both pH and temperature.

Question 20

What is the optimum temperature for human enzymes?

Answer 20

Human enzymes have an optimum temperature of 37 c.

Question 21

Why does enzyme activity increase when the temperature increases from 0c to 37c?

Answer 21

The enzyme and substrate molecules move more quickly at higher temperatures, substrates collide more often with enzyme active sites therefore more reactions take place.

Question 22

Explain the term “denatured” in terms of human enzymes.

Answer 22

As the temperature rises above 37c, the chemical bonds break changing the shape of the enzyme. Since the activity of the enzyme will depend on the shape of its active site, and this has changed, the enzyme will stop working. The enzyme is said to be denatured. It is permanently inactive.

Question 23

What is the effect of temperature on enzyme activity?

Answer 23

As temperature increases enzyme activity also increases until an optimum temperature is reached after which enzyme activity decreases.

Question 24

What does the pH scale measure?

Answer 24

The pH scale measures acidity and alkalinity.

Question 25

Explain the pH scale.

Answer 25

0-6.9= acid
7=neutral
8-14=alkali

Question 26

What is meant by optimum pH?

Answer 26

Although many enzymes are most active at around neutral (pH7), different enzymes have a pH at which they are most active. This is called their optimum pH.

Question 27

What happens when an enzyme is above or below optimum pH?

Answer 27

Above and below an enzyme’s optimum pH, the enzyme is denatured, therefore its activity is reduced.