Lesson #11: Enzymes in
digestion
Objective:
- Identify the main enzymes in digestion and their
functions
Practical
1. Label the boiling tubes A & B
2. Fill each tubing with 8ml of starch.
3. Wash one of the tubes very well and place it in boiling
tube A.
4. Add 3ml of amylase solution in the other tube.
Shake. Wash very well and place in boiling tube B.
5. Place both boiling tubes in the water bath for 30
minutes.
6. Test the water in the boiling tube for starch and
glucose using iodine and benedict’s solution
7. Record your results.
Digestive Enzymes
• There are 3 main types of digestive enzymes:
Enzyme
Amylase
Reaction catalysed
Where produced
Starch → sugars
Salivary glands, pancreas,
small intestine
Stomach, pancreas, small
intestine
Protease
Proteins → amino acids
Lipase
Lipids → fatty acids + glycerol Pancreas, small intestine
Digestive Enzymes
Amylase
Glucose
Starch
Protease
Protein
Amino
Acids
Digestive Enzymes
Lipase
Glycerol
Fatty Acid
Fatty Acid
Fatty Acid
Fat
Fatty Acids
and Glycerol
Amylase
enzyme
Starch
molecule
The enzyme fits over
the substrate perfectly
– like a key fits a lock.
It holds the starch
molecule in place as a
water molecule breaks
the bond between two
glucose particles
This continues until
the molecule has
been broken down
completely
Digestion Summary
Chemical digestion:
• Salivary amylase: starch  maltose
• Pepsin in stomach: protein  peptides
• Pancreatic amylase: starch  maltose
• Trypsin from the pancreas: protein  peptides
• Lipase from the pancreas: fats  glycerol + fatty acids
What factors affect the rate of reaction
of enzymes
• How do you think you can speed up the rate
of an enzymic reaction?
(Hint: It’s the same as any other reaction!)
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