Revision lesson on
enzymes
AQA Unit 2 Additional
Biology
What are enzymes and what do
they do?
Enzymes are Protein molecules (made up of amino acids)
 Biological catalysts (Increase the speed of
chemical reactions)
 Specific (Each one catalyses one particular
reaction)
 Reusable (Can be used again and again)
 Affected by temperature and pH.
 Found in animals, plants and microorganisms.
2 main types of enzymes


Catabolic enzymes which (break down) large
molecules into smaller molecules
e.g. digestion of starch by the enzyme amylase
into glucose.
Anabolic enzymes which (build up) small
molecules to form larger molecules
e.g. production of glucose during
photosynthesis from carbon dioxide, water and
light.
Enzymes and activation energy



Chemical reactions take place when
particles collide with enough energy.
The minimum amount of energy required
is called the activation energy.
Enzymes lower the amount of activation
energy required, so the reaction can
proceed at a greater rate.
Structure of an enzyme
molecule


Enzymes are
proteins made up on
long chains of amino
acids.
These long chains
fold to produce a
special shape which
is vital for the
enzyme‘s function.
Active
Site
How enzymes work
Step-by-step





Shape of the enzyme’s active site is
complimentary to the shape of one particular
substrate.
The two bind together to form an enzymesubstrate complex.
The reaction between them take place rapidly.
The products are released from the enzyme’s
active site.
Complete Qu 1-8 on your worksheet.
Factors affecting enzyme action
- Temperature


Enzymes work faster
as the temperature
increases up to 40oC,
but are eventually
denatured at about
60oC.
This is because the
shape of the active
site is lost.
Factors affecting enzyme action
– pH


Each enzyme works best at a particular pH. This is known as the
optimum pH.
Extremes of pH will cause the active site to denature.
Answer Qu 8- 11 on your worksheet
Enzymes in digestion


Enzymes break down large
insoluble food molecules
into smaller, soluble ones
which can be absorbed
through the small intestine
wall to enter the
bloodstream.
Different parts of the
digestive tract have different
pH conditions to enable
different enzymes to work.
The main groups of digestive
enzymes



Lipase enzymes
digest fatty
substrates.
Protease enzymes
digest protein
substrates.
Carbohydrase
enzymes digest
carbohydrate
substrates.
Substrate Enzyme
Product
Where
Optimum
enzyme
pH
produced
Starch
Glucose
Salivary pH7
glands &
pancreas
Amino
acids
Stomach, pH3
pancreas,
& small
intestine
Fatty
acids &
glycerol
Pancreas pH8
Amylase
(a carbohydrase)
Protein
Trypsin
(a protease)
Lipids
Lipases
(fats)
The action of bile



It’s produced by the liver and is stored in
the gall bladder which, squirts it into the
small intestine.
It’s alkaline to neutralise acidic chyme
coming from stomach.
It emulsifies fats to break them into
smaller droplets which increases the
surface area for lipase enzymes to work.
Commercial use of enzymes
Product
Enzymes
Explanation
Biological washing
powder
Lipases and
proteases.
Digest biological
stains off clothes.
Baby food
Proteases
Pre-digest protein to
make digestion
easier for babies.
Slimming foods
Isomerase
(carbohydrase)
Converts glucose
into fructose (less of
which is needed to
sweeten food).
Complete Qu 12- 17on worksheet.