Download How do digestive enzymes work

How do digestive enzymes work and
where are they produced?
Baseline (Flightpath D): To be able to state that enzymes are used in
digestion to break down food molecules and identify that
carbohydrases break down carbohydrates, proteases break down
proteins, and lipases break down lipids.
Further (Flightpath C&B ): To be able to explain why enzymes are
needed for digestion. For each food molecule, name the enzyme
that acts on it, where it is produced, and which products are formed.
Challenge Flightpath A):to be able to suggest how to test for
substrates and products in a model gut and make a prediction with a
clearly structured scientific explanation.
Write a question that has one of the
key words as the answer
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enzyme
catalyst
active site
substrate
lock and key model
denature
digestion
carbohydrate
lipid
protein
Reaction rates
• Two people walk to school. Sam’s journey is 1
km and it takes him 20 minutes. Ruby walks
0.5 km in 15 minutes. Ask students to work
out who walked at the fastest mean rate?
Starch molecules –
large and branched
Amylase – digestive
enzyme
Breaks down starch to
Maltose
Still too big!
Maltase in the small
intestine breaks down
maltose to glucose
units
Readily absorbed.
Proteins – large and branched
Amino acid
Amino
acid
Amino
acid
Amino acid
Trypsin from the pancreas
Amino acid
Amino
acid
Amino
acid
Amino acid
Breaks down proteins into
peptides.
Amino acid
Amino
acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino
acid
Still too big!
Amino
acid
Peptidase from the small
intestine
Amino acid
Amino
acid
Amino acid
Amino
acid
Amino
acid
Amino acid
Fats &
Oils
Fatty acids and
glycerol which is
easily absorbed.
Bile from the liver mixes
with the ‘fat’ to make an
emulsion
Lipase from the
pancreas breaks
down the fats to...
What are enzymes made of?
Enzymes are protein molecules, and so are made up of amino acids. Most
enzymes contain between 100 and 1,000 amino acids.
These amino acids are joined together in a long chain, which is folded to
produce a unique 3D structure.
Why is shape important?
The shape of an enzyme is very important because it has a direct effect on
how it catalyzes a reaction.
Why do enzymes have different shapes?
An enzyme’s shape is determined by the
sequence of amino acids in its structure,
and the bonds which form between the
atoms of those molecules.
Different types of enzymes have different shapes and functions because
the order and type of amino acids in their structure is different.
Why are enzymes so specific?
Enzymes are very specific about which reactions they catalyze. Only
molecules with exactly the right shape will bind to the enzyme and react.
These are the reactant, or substrate, molecules.
The part of the enzyme to which the
reactant binds is called the active site.
This is a very specific shape and the
most important part of the enzyme.
Enzymes: true or false?
What happens at the active site?
In the same way that a key fits into a lock, so a substrate is thought to fit into
an enzyme’s active site. The enzyme is the lock, and the reactant is the key.
↔
+
enzyme
+
reactant
↔
↔
enzyme-reactant
complex
+
↔
enzyme
+
products
The lock and key model
Digestion in the stomach
When food enters the stomach it stimulates the secretion of hydrochloric
acid (HCl) from the stomach wall. HCl increases the acidity of the stomach
to about pH2 – the optimum pH for stomach enzymes.
oesophagus
mucus cells
gastric gland
parietal cells
(acid-producing)
duodenum
Match the reactant
Digestion in the small intestine
Digestive enzymes found in the small intestine are damaged by a strongly acidic
pH.
How does the body avoid this problem?
The liver produces bile (an alkali), which is stored in the gall bladder and
released into the small intestine.
hepatic
duct
Bile neutralizes the acidic
contents coming from the
stomach, creating the alkaline
gall
environment that the intestinal
bladder
enzymes need to work.
pancreas
duodenum
bile duct
Factors affecting enzymes
The rate of enzyme–catalyzed reactions depends on several factors. What are
some of these?
Factors that affect the rate of a reaction include:
 temperature
 substrate concentration
 pH
 surface area
 enzyme concentration
 pressure.
All enzymes work best at only one particular temperature and pH: this is
called the optimum.
Different enzymes have different optimum temperatures and pH values.
Enzyme inhibitors
Factors affecting enzymes
If the temperature and pH changes sufficiently beyond an enzyme’s optimum, the
shape of the enzyme irreversibly changes.
This affects the shape of the active site and means that the enzyme will no
longer work.
When this happens the enzyme is denatured.
heat
pH
normal
denatured
Enzymes in the home
How many items are made using enzymes?
• Exam question
Mark Scheme
a) (i) stomach
(ii) small intestine
B)
1
1
salivary
glands
stomach
pancreas
small
intestine
amylase
✓
✕
✓
✓
lipase
✕
✕
✓
✓
protease
✕
✓
✓
✓
1 mark per correct row or if no correct row max 1 mark for any one correct column
(c)
enzyme / protease / pepsin most effective in acid conditions / low pH
accept optimum / correct pH
do not accept ref to incorrectly named enzymes
ignore killing bacteria
ignore acid breaks down food
• (d)
Enzyme
Breakdown products