Polypeptide

Polypeptides, are chains of amino acids joined by peptide bonds. Polypeptides can be of any size ranging from just a few amino acids in length to the amounts of proteins and enzyme which can contain hundreds and even thousands of amino acids. The sequence of amino acids is encoded by our DNA, each three base pair sequence, called a codon, codes for a specific amino acid. Peptides bonds are formed by a condensation reaction between the amino group (NH₂) of one amino acid and the carboxyl group (COOH) of another amino acid.

http://cmgm.stanford.edu/biochem/biochem201/Slides/Protein%20Structure/

http://cmgm.stanford.edu/biochem/biochem201/Slides/Protein%20Structure/Forming%20Peptide%20Bond.JPG