Enzymes
Introduction to Enzymes
 Chemical reactions all occur at
different rates
 Some are very quick and some
are extremely slow
Introduction to Enzymes
• We can speed up some chemical
reactions by:
1. increasing the temperature
2. adding a catalyst
• Since it is not always appropriate
increasing the temperature of a living
organism, biological catalysts called
ENZYMES are used to increase the
rate of reaction.
Enzymes
• An enzyme is a substance which can speed
up a reaction without itself being altered.
• There are 3 important points that are true
for all enzymes and catalysts:
1. When an enzyme is present, the reaction
requires less energy to start.
2. When an enzyme is present, the reaction is
quicker
3. An enzyme remains unchanged during the
reaction and can be reused.
Breakdown of Hydrogen
Peroxide
• Hydrogen Peroxide (H₂O₂) is a harmful
by-product of reactions inside cells.
• H₂O₂ can be broken down into water
(H₂O) and oxygen (O₂).
Hydrogen peroxide
(H2O2)
Water + Oxygen
(H2O)
(O2)
Enzymes
• Enzymes are biological catalysts
• Catalase is an enzyme made by living
cells, which can breakdown hydrogen
peroxide
• When a piece of living tissue is added,
you can see bubbles of oxygen released
• The more bubbles released, the more
catalase is present in the tissue.
Questions
1. What is meant by activation energy?
2. State 3 properties of a catalyst.
3. Where are enzymes found in living
organisms?
4. Of what type of organic substance are
enzymes composed?
5. Briefly explain why enzymes are needed
for the functioning of all living cells.
Enzymes
• Catalase can only speed up the
breakdown of hydrogen peroxide, NO
OTHER REACTION.
• It is said to be specific
• Each enzyme can catalyse only one
reaction
• The substance that the enzyme
catalyses is called the substrate
Enzymes
• Enzymes have an area on their surface
which is a specific shape.
• It is here that the substrate attaches.
• This area is known as the active site.
• The shape of the active site is
determined by its chemical structure
which results from bonding between
amino acids in the enzyme molecule.
Enzymes
• The active site and substrate are said
to be complementary
• The substrate locks onto the enzyme at
the active site and the reaction occurs.
• This is known as the ‘lock and key’
theory.
Enzymes
• The reaction produces the products of
the reaction.
• Some enzymes are responsible for
breaking down large substrates into
small products
• Some enzymes are responsible for
building up small substrates into large
products
Questions
1. What determines the shape of an
enzymes active site?
2. What name is given to the substance on
which an enzyme acts?
3. Why is an enzyme said to be specific?
4. How is an enzyme thought to act
according to the lock and key
hypothesis?