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

An amino acid molecules

H2Namino group

COOHcarboxyl group

C

R

H

The condensation and hydrolysis of a polypeptide

5

1 4

3

2

1 2 3 4 5

hydrolysiscondensation

Condensation of two amino acid to form a dipeptide

H2N C

R1

H

C

O

OH HN

H

C

H

R2

COOH

H2N C

R1

H

O

H

C

H

R2

COOHC---N

H2O

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

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