Page 37 - Biology Form Two
P. 37
Biology for Secondary Schools
Safety precautions (iii) Proteins react with sodium
Do not taste any food in the hydroxide (NaOH) and copper
laboratory. Handled all chemicals sulphate (CuSO ) to produce a
4
with care. violet or purple colour. This is
called the Biuret test.
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5. Observe and record what happens.
6. Tabulate your results showing the (iv) The Biuret test can be used to
identify a protein substance and
food sample tested, procedures, confirm its presence.
observation and inference.
Proteins are organic food substances
Food
sample Procedures Observation Inference consisting of carbon, hydrogen, oxygen,
tested and nitrogen. They are large molecules
made up of chains of amino acids. There
are about 23 different types of amino
Question acids in proteins. Each amino acid
What changes did you observe? behaves as an acid as well as a base,
meaning it has amphoteric properties.
The following activities will help you
Test for proteins to identify properties of protein.
Protein is a major nutrient that is
essential for growth, building body
parts and repair damaged cells. It is Activity 1.8: Investigate the presence of
the major building block of human protein in egg white using the Biuret test
body responsible for building and Materials
maintaining body tissues. The main Egg white, water, test tubes, test tube
sources of protein are chicken, fish, holder, droppers, measuring cylinder (10
milk, beef, eggs, beans, soybeans, and
soybean products. ml), 1M sodium hydroxide solution, and
1% copper sulphate solution
Properties of proteins
(i) Proteins are insoluble in water. Procedure
1. Pour 3 ml of water into a test tube
(ii) They coagulate on heating. This followed by 2 ml of egg white and
means small particles of protein shake well.
clump together to form bigger 2. Add 2 ml of 1M sodium hydroxide
particles when a mixture of protein solution to a test tube containing
and water is heated. The process the mixture of protein and water.
is called denaturation.
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