1. Proteins
 are compounds of carbon, hydrogen, oxygen,
nitrogen and sometimes sulphur, phosphorus
 amino acids:
– unit of proteins
– about 20 different types
– essential and non-essential types

2. An amino acid molecules
H2N
amino group
COOH
carboxyl group
R
C
H

3. The condensation and hydrolysis of a
polypeptide
1 4
condensation hydrolysis
1 2 3 4 5

4. Condensation of two amino acid to form a
dipeptide
R1
H2N C
H
C
O
OH H
N
H
H
C
R2
COOH
R1
H2N C
H
O
C---N COOH
H
H
C
R2
H2O

5. Functions of proteins
 components of cell membranes and cytoplasm
 for growth and repair of body cells
 for making enzymes, hormones, antibodies and
haemoglobin
 provide energy during starvation
 excess protein is under deamination in the liver
 deficiency disease: Kwashiorkor

6. Test for proteins / Biuret test
egg white solution
1 cm3 NaOH solution
Put CuSO2 solution drop by
drop, and shake the mixture
after addition of each drop
Positive result: purple colour