More than 50% of most cells are proteins - uses include:

• In cell membranes - protein channels for transport

• Haemoglobin - carries oxygen

• Antibodies - bind to antigens in immune response

• Enzymes - catalyse and control thousands of metabolic reactions

• Hair and skin contain keratin

• Collagen for strength in many tissues

Proteins are polymers of amino acids

There are around 20 amino acids in living organisms

From these are made the thousands of proteins needed by living organisms

Structure of AMINO ACIDS

All amino acids have the following structural elements:

1. An Amine group (–NH2)

2. A Carboxylic acid group (–COOH)

3. A central Carbon atom

4. H atom attached to the central carbon atom

5. A side group – usually called the R group. This varies from one amino acid to another and can be as simple as a Hydrogen atom or a complex Carbon ring structure