Proteins are large molecules made up of long chains of amino acids. Amino acids are the building blocks of proteins. The biochemical activity of proteins is characterised by their individual structure, size and shape. These factors are determined by the sequence and characteristics of the constituent amino acids.
There are about 20 different amino acids commonly found in plant and animal proteins. For adults, 8 of these, have to be provided in the diet and are therefore defined as ‘essential’ or ‘indispensable’ amino acids. These are:
In children, arginine, histidine, cysteine, glycine, tyrosine, glutamine and proline are also considered to be essential (indispensable) amino acids, because children are unable to make enough to meet their needs. These are referred to as ‘conditionally’ essential. There may also be certain disease states during adult life when a particular amino acid becomes conditionally essential.
The other amino acids do not have to be provided by the diet. This is because the amino group of these amino acids can be transferred to another amino acid with a different amino group by a process called transamination. In this way the body is able to make some amino acids itself. These are known as ‘non-essential’ or ‘dispensable’ amino acids.