• Proteins are composed of long chains of amino acids.
• Catalysts are a form of protein.
• Natural catalysts are called enzymes.
• The active site of an enzyme will only fit specific substrate molecules.
• Enzymes are sensitive to temperature and pH levels. If the temperature is too high or the pH level too alkaline or acidic then the enzyme is denatured.
• Enzymes work better at higher temperatures but not too high.
• Some enzymes work better in acidic conditions and some in alkaline.
• The three main digestive enzymes are protease, lipase and amylase.
• Enzymes in the stomach work better in acidic conditions while enzymes in the small intestine work better in alkaline conditions.
• Enzymes are used for industrial purposes because they save money on energy-demanding equipment.

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TEST IT!

1. A baby food company is trying to design a new baby food. Babies find it hard to digest protein and so the company uses enzymes in order to digest the proteins in the food. Complete the sentences using the words below.

amino acids / fatty acids / lipases / glucose / proteases

a) _______________ are used to break down proteins.

b) Proteins are broken down into _______________

c) _______________ break down fats.

2. A group of scientists wanted to look into how milk fat is broken down by a particular enzyme. The reaction mixture they used contained milk and the enzyme they wanted to investigate.

In experiment 1 they also added bile.

In experiment 2 they used water instead.

The pH was taken every 2 minutes, The results were as follows.

Time (minutes)	pH
	Experiment 1	Experiment 2
2 4 6 8 10	8.8 8.6 8.5 8.0 7.6 7.4	8.8 8.8 8.8 8.6 8.5 8.3

a) Milk fat is a sort of lipid. Why was there a change in pH in experiment 2?

b) Why was there a difference in the rate at which the pH dropped when bile was present?

3. Enzymes are found in the body and either break down large molecules are join together smaller molecules

a) Which enzyme breaks down which substance?

amylase starch

lipase protein

protease fat

4. Complete the table below:

Original substance	Broken down into
Starch Protein Fat

1. Bile is one enzyme produced in the body.

i. Where is it made?

ii. Where is it stored?

ANSWERS

a) Proteases…

b) …amino acids

c) Lipases…

a) The enzyme used must be a lipase. Fatty acid is produced which lowered the pH.

b) Bile provided the best pH conditions for the enzyme and so the rate of reaction increased.

a) amylase ? starch

lipase ? fat

protease ? protein

b)

Original substance	Broken down into
Starch Protein Fat	Sugars Amino acids Fatty acids

c)

i. The liver

ii. The gallbladder
Section complete!