Cells & Enzymes
Made of protein
Present in
all living cells
Converts substrates
into products
Enzymes
Biological
catalysts
Increase the rate of
chemical reactions
Remain unchanged
by chemical reaction
Chemical Reactions
A chemical reaction takes place when one or
substances is chemically changed into one or more
different substances.
Chemical reactions take place in cells all the time.
Catalyst
Product
Substrate
Enzyme
Hydrogen
peroxide
Manganese
dioxide
Water + oxygen
Catalase
Catalysts
A catalyst is a substance which speeds up a chemical
reaction, without itself being changed by the
reaction.
1. When a catalyst is present, less energy is needed
to get the chemical reaction started.
2. When a catalyst is present, the speed of the
chemical reaction is faster.
3. Although a catalyst helps a chemical reaction to
happen, it is unchanged at the end of the reaction.
Biological Catalysts
The biological catalyst present in the cytoplasm of
plant and animal cells that speeds up the breakdown
of hydrogen peroxide is called CATALASE.
Hydrogen
peroxide
catalase
Oxygen + water
2.2 Nature of Enzymes
The biological catalyst present in the cytoplasm of
plant and animal cells that speeds up the breakdown
of hydrogen peroxide is called CATALASE.
Hydrogen
peroxide
Catalase
Water + oxygen
Catalase cannot speed up any other reaction. It is
SPECIFIC to this reaction.
One Enzyme – One Reaction
There are thousands of different enzymes in your
body.
Why are there so many different enzymes?
Each enzyme has its own unique protein structure
and shape, which is designed to match or
COMPLEMENT its substrate.
Lock & Key Hypothesis
An enzyme only acts on one type of substance, or substrate.
Therefore, the enzyme is said to be SPECIFIC to its one substrate.
The shape of the active site (binding site) of the enzyme, matches the
shape of the substrate. Allowing the two molecules to bind during the
chemical reaction.
This theory of enzyme action is called the ‘lock-and-key’ hypothesis.
MOVIE
Different enzymes for different jobs
Enzymes involved in breakdown reactions
Enzyme and substrate separate
Enzyme-substrate complex
Enzyme and products separate
Enzymes involved in synthesis reactions
Enzyme and substrates separate
Enzyme-substrates complex
Enzyme and product separate
2.3 Using a Control
Why is it necessary to include a control experiment
in an investigation?
A control is an experiment that allows a
comparison within an investigation in order to
ensure that the conclusions drawn from the results
are valid.
2.3 Using a Control
Only one variable should be altered in an
investigation, this is said to be the altered variable.
What was the altered variable in the last
investigation you carried out?
It is important to ensure that all other potential
variables are kept the same in the investigation,
these are called the controlled variables.
What were the controlled variables in the last
investigation you carried out?
Enzymes involved in breakdown reactions
Hydrogen peroxide
Starch
Fat
Protein
Catalase
Amylase
Lipase
Pepsin
Water + Oxygen
Maltose
Fatty acids + Glycerol
Amino acids
2.4 Synthesis reactions
Leaves make glucose.
Glucose is used by
leaves as energy
source or transported
to root for storage.
Roots convert glucose
into G-1-P.
Phosphorylase
converts G-1-P into
starch.
2.4 Synthesis reactions
What is phosphorylase?
Phosphorylase is an enzyme that synthesises starch.
What is substrate of phosphorylase?
Glucose-1-phosphate
What is the product?
Starch
phosphorylase
glucose-1-phosphate
starch
2.4 Synthesis reactions
Amylase catalyses the breakdown of starch to
produce maltose.
How is starch produced?
phosphorylase
glucose-1-phosphate
starch
2.5 Effect of High Temperature
• Optimum conditions are the conditions
at which an enzymes works best
• Rate of reactions may be affected by
temperature and pH
Notes on Denaturation
Notes on Optimum temp
2.5 Effect of High Temperature
What happens to the activity of an enzyme at high
temperatures?
Notes on Denaturation
Notes on
Optimum temp
Effect of pH on enzymes
When the pH changes outwith optimal conditions, the shape
of the active site of the enzyme alters and the enzyme is
Movie
denatured.
Effect of pH on enzyme activity
Most enzymes work best at a pH close to neutral (pH7), but
there are some exceptions. Pepsin, an enzyme found in the
stomach, has an optimum pH of 2.
Enzyme Summary
Enzyme
Substrate Product(s) Degradation
or synthesis?
Amylase
Starch
Maltose
Degradation
Catalase
Hydrogen
peroxide
Protein
Oxygen and
water
Amino acids
Degradation
Pepsin
Phosphorylase
Lipase
Glucose-1Starch
phosphate
Fat
Amino acids
Degradation
Synthesis
Degradation