Protein

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Proteins are one of the main building blocks in living things. They have two main uses in living things:

Protein is often used as a building material. For example, skin, hair, nails and the tough outer skins of insects are made mostly of protein.
Perhaps more important, some proteins do work on other molecules. Proteins which do these jobs are called enzymes.

Proteins are made from molecules called amino acids, arranged in long chains (like the one shown here), or in flat sheets, or rolled up like a ball of string.