Topic 1 - 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

upside down U

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

kinda like ^ but with lil flares

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

little rise then flat

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) or are 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?

Answer 27

Measured using calorimetry

Question 28

What is calorimetry?

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

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?

Answer 30

energy = energy in food / mass of food burnt