To make a protein, amino acids are linked together in a long chain. The chain is then bundled into to a three-dimensional structure, like a tangled ball of yarn. Although there are hundreds of different amino acids, only 21 are used in animal proteins.

Proteins are the essential building blocks of all tissues and organs of the body including:

• cartilage, tendons and ligaments (collagen and elastin)
• the element of muscles that contract (actin and myosin)
• skin, hair and nails (keratin)
• blood proteins (haemoglobin, transferrin, albumin and globulins)
• enzymes
• hormones
• antibodies

Proteins are often described as the 'backbone' of cells because they have a structural role in all cell walls. Proteins are required for all tissue growth, replenishment and repair.