Every type of protein is constructed of a long sequence of amino acids, which are organic compounds made up of carbon, oxygen, and hydrogen atoms. Amino acids are joined together by peptide bonds (green) to form an amino acid chain, called a peptide. When more than 4 amino acids bond together, it is called a polypeptide. These chains can contain hundreds of amino acids.

The twenty amino acids can be conjoined and reordered in so many varieties as to yield hundreds of thousands of different protein types. With just two amino acids joined by a single peptide bond, constituting a dipeptide chain, there are 400 possible combinations. With three amino acids (a tripeptide), 8000 combinations. Variables include the number and type of amino acids combined; their sequence along a chain; the number of peptide bonds linking them together; the shapes assumed as polypeptide chains fold; and the three-dimensional structure of a chain or of multiple chains linked together.

This model shows 4 amino acids joined by peptide bonds. Carbon atoms are dark gray, hydrogen atoms are white, nitrogen atoms are blue, radicals are purple, peptide bonds are green, and oxygen atoms are red.

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