Core Concepts (Enzymes) Flashcards
Define metabolism
The sum of all the enzyme controlled
chemical reactions taking place in a cell.
State the two main types of reactions
that make up metabolism.
Anabolic and catabolic reactions.
What is anabolism?
A set of metabolic pathways that
synthesise complex molecules from
smaller, simpler molecules.
What is catabolism?
A set of metabolic pathways that
breakdown complex molecules into
smaller, simpler molecules.
What is an enzyme?
● A biological catalyst used to speed up the
rate of intracellular and extracellular
biochemical reactions
● Not used up or permanently altered
What is an enzyme?
● A biological catalyst used to speed up the
rate of intracellular and extracellular
biochemical reactions
● Not used up or permanently altered
What is an intracellular enzyme?
An enzyme that acts within cells, e.g.
catalase.
What is an extracellular enzyme?
An enzyme that is secreted by cells and
functions outside of cells, e.g. amylase.
What is the active site of an enzyme?
A region on an enzyme that is
complementary to the shape of a specific
substrate. The substrate binds and the
reaction takes place.
Why is an active site described as
‘specific’?
● 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
Define activation energy
The minimum amount of energy
required for a reaction to take place.
What is catalysis?
● 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
Describe the ‘lock and key’ model.
- Substrate(s) and the active site of the enzyme come into contact
- Substrate(s) binds, enzyme-substrate complex forms
- Reaction takes place, product(s) formed in an enzyme-product
complex - Product(s) released from the active site. The active site is now
free to bind to another substrate
What is the induced-fit hypothesis?
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.
What factors affect the rate of an
enzyme-controlled reaction?
● Temperature
● pH
● Substrate concentration
● Enzyme concentration
How does temperature affect the rate of
enzyme-controlled reactions?
● 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
Explain how increasing temperature
above the optimum affects the rate of an
enzyme-controlled reaction
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
Draw a graph to show the effect of
increasing temperature on the rate of an
enzyme-catalysed reaction.
How does pH affect the rate of
enzyme-controlled reactions?
● 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
Draw a graph to show the effect of
increasing pH on the rate of an
enzyme-catalysed reaction.
What is a buffer?
A molecule that maintains a constant pH
in a solution when small volumes of acid
(H+) or base(OH-) are added.
How does substrate concentration affect
the rate of an enzyme-controlled
reaction?
- 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
How does enzyme concentration affect
the rate of an enzyme-controlled
reaction?
- 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)
What is a competitive inhibitor?
A molecule which competed for the active
site of an enzyme, blocking it and
preventing the substrate from binding.
Is competitive inhibition temporary or
permanent?
Competitive inhibition is generally temporary.
However, in some cases (e.g. aspirin) it may
be permanent.
How does increasing substrate
concentration affect competitive
inhibition?
● Increase in substrate concentration
● More substrate than inhibitor
● Rate of reaction increases
What is a non-competitive inhibitor?
● 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
Is non-competitive inhibition temporary
or permanent?
Permanent
How does increasing substrate
concentration affect non-competitive
inhibition?
Increasing the substrate concentration
will not overcome the effect of the
non-competitive inhibitor.
What are immobilised enzymes?
Enzymes which are attached to an inert,
insoluble material over which the substrate
passes and the reaction takes place.
Give an example of an application of
immobilised enzymes.
Biosensors
Why are immobilised enzymes important
in industrial processes?
● Enables enzymes to be reused
● Improves enzyme stability in variable/extreme
temperatures and pH
● Increases the efficiency of reactions
