Core Concepts (Enzymes)

Question 1

Define metabolism

Answer 1

The sum of all the enzyme controlled
chemical reactions taking place in a cell.

Question 2

State the two main types of reactions
that make up metabolism.

Answer 2

Anabolic and catabolic reactions.

Question 3

What is anabolism?

Answer 3

A set of metabolic pathways that
synthesise complex molecules from
smaller, simpler molecules.

Question 4

What is catabolism?

Answer 4

A set of metabolic pathways that
breakdown complex molecules into
smaller, simpler molecules.

Question 5

What is an enzyme?

Answer 5

● A biological catalyst used to speed up the
rate of intracellular and extracellular
biochemical reactions
● Not used up or permanently altered

Question 6

What is an enzyme?

Answer 6

● A biological catalyst used to speed up the
rate of intracellular and extracellular
biochemical reactions
● Not used up or permanently altered

Question 7

What is an intracellular enzyme?

Answer 7

An enzyme that acts within cells, e.g.
catalase.

Question 8

What is an extracellular enzyme?

Answer 8

An enzyme that is secreted by cells and
functions outside of cells, e.g. amylase.

Question 9

What is the active site of an enzyme?

Answer 9

A region on an enzyme that is
complementary to the shape of a specific
substrate. The substrate binds and the
reaction takes place.

Question 10

Why is an active site described as
‘specific’?

Answer 10

● The 3D structure of each enzyme (including the active
site) is unique due to the presence of different side
chains and branches
● Only specific substrates complementary to the active
site can bind

Question 11

Define activation energy

Answer 11

The minimum amount of energy
required for a reaction to take place.

Question 12

What is catalysis?

Answer 12

● An increase in the rate of a chemical reaction
using a catalyst (such as an enzyme)
● The catalyst lowers the activation energy of
the reaction

Question 13

Describe the ‘lock and key’ model.

Answer 13

1. Substrate(s) and the active site of the enzyme come into contact
2. Substrate(s) binds, enzyme-substrate complex forms
3. Reaction takes place, product(s) formed in an enzyme-product
   complex
4. Product(s) released from the active site. The active site is now
   free to bind to another substrate

Question 14

What is the induced-fit hypothesis?

Answer 14

A model of enzyme action which states that once a
specific substrate binds to the active site, the enzyme
undergoes subtle conformational changes. This puts
a strain on the substrate, lowering the activation
energy for the reaction.

Question 15

What factors affect the rate of an
enzyme-controlled reaction?

Answer 15

● Temperature
● pH
● Substrate concentration
● Enzyme concentration

Question 16

How does temperature affect the rate of
enzyme-controlled reactions?

Answer 16

● As temperature increases molecules have more KE
● Molecules moves faster and collide more frequently
● More enzyme-substrate complexes form
● Rate of reaction increases
● Rate peaks at the optimum temperature

Question 17

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

Answer 17

An increase in temperature increases kinetic energy of particles, so collision frequency increases and more enzyme-substrate complexes are formed, therefore rate of reaction increases.
● Temperature increases above the optimum
● Increased vibrations break hydrogen and ionic bonds in tertiary structure
● Active site changes shape, enzyme is denatured
● No more enzyme-substrate complexes can form
● Rate of reaction decreases

Question 18

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

Answer 18

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.toppr.com%2Fask%2Fcontent%2Fconcept%2Feffect-of-temperature-and-ph-on-enzyme-activity-265695%2F&psig=AOvVaw2LvEokayc_Kq9qv_CCAl8X&ust=1675125553394000&source=images&cd=vfe&ved=0CBAQjhxqFwoTCLinlfuH7vwCFQAAAAAdAAAAABAE

Question 19

How does pH affect the rate of
enzyme-controlled reactions?

Answer 19

● Enzymes have an optimum pH
● pH shifts from the optimum
● Hydrogen and ionic bonds in the tertiary structure are altered
● Interaction of polar and charged R-groups changes
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases

Question 20

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

Answer 20

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.toppr.com%2Fask%2Fcontent%2Fconcept%2Feffect-of-temperature-and-ph-on-enzyme-activity-265695%2F&psig=AOvVaw2LvEokayc_Kq9qv_CCAl8X&ust=1675125553394000&source=images&cd=vfe&ved=0CBAQjhxqFwoTCLinlfuH7vwCFQAAAAAdAAAAABAE

Question 21

What is a buffer?

Answer 21

A molecule that maintains a constant pH
in a solution when small volumes of acid
(H+) or base(OH-) are added.

Question 22

How does substrate concentration affect
the rate of an enzyme-controlled
reaction?

Answer 22

• If enzyme concentration is fixed, the rate of
  reaction increases proportionally to the
  substrate concentration.
• Once all active sites become full, the rate of
  reaction remains constant (graph plateaus).
  Enzyme concentration is a limiting factor

Question 23

How does enzyme concentration affect
the rate of an enzyme-controlled
reaction?

Answer 23

• If substrate concentration is fixed, the rate of
  reaction increases proportionally to the
  enzyme concentration.
• When all of the substrates occupy active
  sites, the rate of reaction plateaus (substrate
  concentration is a limiting factor)

Question 24

What is a competitive inhibitor?

Answer 24

A molecule which competed for the active
site of an enzyme, blocking it and
preventing the substrate from binding.

Question 25

Is competitive inhibition temporary or
permanent?

Answer 25

Competitive inhibition is generally temporary.
However, in some cases (e.g. aspirin) it may
be permanent.

Question 26

How does increasing substrate
concentration affect competitive
inhibition?

Answer 26

● Increase in substrate concentration
● More substrate than inhibitor
● Rate of reaction increases

Question 27

What is a non-competitive inhibitor?

Answer 27

● An inhibitor which binds to a different part of an enzyme, the
allosteric site
● The tertiary structure of the enzyme (including the active site)
changes shape
● The active site is no longer complementary to the substrate. The
substrate cannot bind and the enzyme is inhibited

Question 28

Is non-competitive inhibition temporary
or permanent?

Answer 28

Permanent

Question 29

How does increasing substrate
concentration affect non-competitive
inhibition?

Answer 29

Increasing the substrate concentration
will not overcome the effect of the
non-competitive inhibitor.

Question 30

What are immobilised enzymes?

Answer 30

Enzymes which are attached to an inert,
insoluble material over which the substrate
passes and the reaction takes place.

Question 31

Give an example of an application of
immobilised enzymes.

Answer 31

Biosensors

Question 32

Why are immobilised enzymes important
in industrial processes?

Answer 32

● Enables enzymes to be reused
● Improves enzyme stability in variable/extreme
temperatures and pH
● Increases the efficiency of reactions