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Step 5: Determine the Amino Acid Sequence
First, the proteins have to be "digested" into their amino acid pieces. Then chemical reactions can determine what amino acids are present.  This used to be a time-consuming and laborious process.  Nowadays, laboratory instruments perform this function automatically, identifying not only what amino acids are present but also their sequence (order.)
The diagram on the right shows how atoms in an amino acid are arranged. Carbon atoms are represented by the letter C,  oxygen atoms by O, Nitrogen by N, and hydrogen by H.  The R stands for the rest of the molecule which is different for each kind of amino acid. aminoacids.jpg (14773 bytes)

The instruments use a chemical reaction that strips off one amino acid at a time, starting at the end with a Nitrogen group. By lopping off one amino acid at one end, the next amino acid has an exposed Nitrogen group, and it in turn can be lopped off and identified.

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