Enzymes

Question 0

The active site (4)

Answer 0

• The shape of the active site is determined by the primary, secondary and tertiary structure
• Every enzyme has a different shaped active site
• Only a few amino acids actually make up the active site
• The active site is complementary in shape to the substrate

Question 1

Characteristics of enzymes (6)

Answer 1

• Generally globular
• Generally soluble
• They act as catalysts
• They are substrate specific
• Have an active site
• Activity is affected by pH and temperature

Question 2

Catalyst

Answer 2

-A substance that speeds up a reaction without being used up in the process

Question 3

Lactase (2)

Answer 3

• Breaks down milk sugar, lactose into glucose and galactose monomers
• Hence lactose intolerant people cannot produce lactase, resulting in stomach cramps

Question 4

Catalase

Answer 4

• Breaks down hydrogen peroxide into water and oxygen gas

- All organisms produce catalase as hydrogen peroxide is toxic if it builds up

Question 5

Ribulose bisphosphate carboxylase

Rubisco

Answer 5

Plants need carbon dioxide for photosynthesise, so the enzyme rubisco catalysed the binding of carbon dioxide to a molecule called ribulose bisphosphate

Question 6

ATP-ase (2)

Answer 6

• Breaks down ATP into ADP and a phosphate group

- This releases a small amount of energy for processes such as active transport

Question 7

Glycogen synthetase (2)

Answer 7

• Catalyses the building up of glycogen by catalysing of glucose molecules
• Glycogen is the storage carbohydrate of animals

Question 8

Enzymes and endotherms (2)

Answer 8

• Endotherms can maintain body heat independently of the environment so enzymes can work at their optimum temperatures
• A high energy diet is needed to maintain such an ability

Question 9

Heterotrophs

Answer 9

-Organisms that obtain their nutrients by consuming other organisms

Question 10

Extracellular enzymes

Answer 10

-Enzymes that catalase reactions outside the cell

Question 11

Intracellular enzymes

Answer 11

-Enzymes that catalase reactions inside the cell

Question 12

Process of phagocytosis (3)

Answer 12

• Phagocyte engulfs pathogen
• Plasma membrane fuses round pathogen and packages pathogen into a vesicle
• Endocytosed vesicle fuses with lysosome and is broken down

Question 13

Activation energy (3)

Answer 13

• The amount of energy that must be applied for a reaction to proceed
• Different reactions require a different activation energy level
• Enzymes reduce the amount of activation energy needed

Question 14

Lock and key mechanism

Answer 14

In this model, the substrate key fits into the active site lock
The substrate is held in one position so the reaction can go ahead

Question 15

Induced fit hypothesis (8)

Answer 15

• As the enzyme active site collides with the substrate, the enzyme molecule changes shape
• This makes the active site fit more closely around the substrate
• The substrate fits in and is held by oppositely charged groups on the substrate and the active site
• Change in enzyme shape places strain on the substrate molecule, destabilising the substrate molecule
• This produces a product called an enzyme product complex
• Products formed are different shapes to the substrate
• Products don’t fit so they move away
• Process is repeated

Question 16

pH

Answer 16

Is a measure of hydrogen ion concentration

The lower the number, the more H+ ions

Question 17

The effect of changing the pH on an enzyme

Answer 17

An increase in H+ ions will result an increase in overall charge around the enzyme
This will cause the ionic bonds and the H-bonds to break as the electrostatic attraction becomes too large
This changes the shape of the active site, thus the enzyme cannot function