Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts that increase the rate
of a chemical reaction without being
permanently altered themselves

Question 2

What is an advantage of enzymes in the

body?

Answer 2

They enable cellular reactions to take

place at lower temperatures

Question 3

What is the active site of an enzyme?

Answer 3

The region of an enzyme to which a
substrate molecule binds and the
reaction takes place

Question 4

Why are enzymes described as having a ‘high specificity’ for their substrate?

Answer 4

Only substrates with a specific,
complementary shape can fit into an
enzyme’s active site

Question 5

Describe the ‘lock and key’ model

Answer 5

1. Substrate collides with the active site of an enzyme
2. Substrate binds, enzyme-substrate complex forms
3. Substrate converted to products
4. Products released from the active site which is now
   free to bind to another substrate

Question 6

What factors affect the rate of an enzyme-controlled

reaction?

Answer 6

● Temperature
● pH
● Substrate concentration

Question 7

Explain how increasing temperature initially affects

the rate of an enzyme controlled reaction

Answer 7

● As temperature increases molecules have more KE
● Movement of molecules increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases

Question 8

Explain how increasing temperature above the
optimum affects the rate of an enzyme controlled
reaction

Answer 8

● Temperature increases above the optimum
● Increased vibrations break bonds in enzyme’s structure
● Active site changes shape, enzyme is denatured
● No more enzyme-substrate complexes can form
● Rate of reaction decreases

Question 9

Draw a graph to show the effect of increasing
temperature on the rate of an enzyme-catalysed
reaction.

Answer 9

https://pmt.physicsandmathstutor.com/download/Biology/GCSE/Notes/Edexcel/1-Key-Concepts-in-Biology/Flashcards/Flashcards%20-%20Topic%201%20Enzymes%20-%20Edexcel%20Biology%20GCSE.pdf

Page 19

Question 10

Explain how pH affects the rate of an enzyme

controlled reaction

Answer 10

● Enzymes have an optimum pH
● pH shifts from the optimum
● Bonds in the enzyme’s structure are altered
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases

Question 11

Draw a graph to show the effect of
increasing pH on the rate of an
enzyme-catalysed reaction

Answer 11

https://pmt.physicsandmathstutor.com/download/Biology/GCSE/Notes/Edexcel/1-Key-Concepts-in-Biology/Flashcards/Flashcards%20-%20Topic%201%20Enzymes%20-%20Edexcel%20Biology%20GCSE.pdf

Page 23

Question 12

Explain how the substrate concentration
affects the rate of an enzyme-controlled
reaction

Answer 12

● Substrate concentration increases
● Number of substrate molecules in the same volume increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
● Once all active sites become full, the rate of reaction plateaus

Question 13

Draw a graph to show the effect of
increasing substrate concentration on
the rate of an enzyme-catalysed reaction

Answer 13

https://pmt.physicsandmathstutor.com/download/Biology/GCSE/Notes/Edexcel/1-Key-Concepts-in-Biology/Flashcards/Flashcards%20-%20Topic%201%20Enzymes%20-%20Edexcel%20Biology%20GCSE.pdf

Page 27

Question 14

How can the rate of an enzyme-controlled reaction

be calculated when given a value for time

Answer 14

rate = 1/time

Question 15

What are the units for rate?

Answer 15

s^-1

Question 16

Why must large organic molecules be broken down

into smaller, simpler molecules in the body?

Answer 16

● Large molecules are too big to be absorbed across
the surface of the gut wall
● ∴ large molecules are broken down into smaller
molecules for absorption into the bloodstream

Question 17

Give an example of the breakdown of large

molecules into smaller molecules in plants

Answer 17

Starch is broken down by enzymes into
simpler sugars which are respired to
release energy

Question 18

What type of molecules are proteins and

carbohydrates?

Answer 18

Polymers

Question 19

What are the monomers of carbohydrates?

Answer 19

Simple sugars

Question 20

Which group of enzymes catalyses the breakdown of

carbohydrates?

Answer 20

Carbohydrases

Question 21

Which type of carbohydrase catalyses the

breakdown of starch?

Answer 21

Amylase

Question 22

What are the monomers of proteins?

Answer 22

Amino Acids

Question 23

Which type of enzyme catalyses the breakdown of

proteins?

Answer 23

Proteases

Question 24

What is the function of lipases?

Answer 24

Enzymes which catalyse the breakdown

of lipids into fatty acids and glycerol

Question 25

Why are small molecules synthesised into larger

organic molecules in the body?

Answer 25

• Large molecules are used for storage (e.g.
  glycogen)
• Used to build structures
  (e. g. organelles).

Question 26

Which enzyme catalyses the formation of glycogen

from glucose?

Answer 26

Glycogen synthase

Question 27

How can the amount of energy contained in food be

measured? (biology only)

Answer 27

Measured using calorimetry

Question 28

What is calorimetry? (biology only)

Answer 28

A method of measuring the heat transfer

during a chemical reaction

Question 29

Describe the method used to measure
the amount of energy in a sample of food
(biology only)

Answer 29

1. Add a set volume of water to a boiling tube, record initial temperature
2. Record the mass of a small sample of food (e.g. bean)
3. Stick the sample onto a mounted needle
4. Using a bunsen burner light the food sample
5. Hold the sample under the boiling tube until it burns up
6. Record the maximum temperature reached by the water
7. Record the final mass of the food sample

Question 30

How can the amount of energy in the
food sample be calculated?
(biology only)

Answer 30

Energy in food (J) = mass of water (g) x temperature change of water (°C) x 4.2

Energy (J/g) = Energy in food (J)/ Mass of food burnt (g)