Biomolecules

| 137

Average composition

of cells

Water

70-90 %

Protein

10-15 %

Carbohydrates

3 %

Lipids

2 %

Nucleic acids

5-7 %

Ions

1 %

1. PRØTËÏÑS

Proteins are

heteropolymer

of amino acids.

They are

polypeptides.

i.e., linear chains

of amino acids

linked by peptide

bonds.

Peptide bond is formed

when –COOH group of one

amino acid reacts with –NH2

group of next amino acid

by releasing a molecule of

water (dehydration).

Peptide bond

Peptide bond

H

H

H

H

H

H

H

H

H

H

H

H

H

N

N

N

N

C

C

C

C

C

C

C

C

OH

OH

OH

O

O

O

O

O

Carboxyl

group

Amino

group

Side

Chain