Peptides are short chains of amino acids linked by peptide bonds. By convention, a peptide is not more than 30-50 amino acids in length. Longer chains of amino acids are called polypeptides or proteins. Wikipedia offers a good discussion of peptides, with examples.
Peptides & Backbones
This is the of 1 amino acid. Adding to the backbone with an additional amino acid on each side gives a (3 amino acids). No side groups are shown, and most hydrogens are omitted. Now each amino acid has a 1 carbon side group so we have (tri-alanine). Adding a carbon chain plus an NH3 on the first amino acid gives . Adding to the 3rd amino acid gives isoleucine: Lys-Ala-Ile. The 4th amino acid is threonine with its hydroxyl, giving . Here is the shape of the (4 AAs). The stick representation has too much detail for larger proteins, so the α-carbons are connected with a line called the . Showing only the makes it easier to see the path of the protein chain (its secondary and tertiary structure).
The above scenes in Jmol were adapted from the chapter Peptides and Backbones in a tutorial on Hemoglobin first written by Eric Martz as a RasMol Movie Script released in March, 1996, which was released as a Hemoglobin Tutorial implemented with Chime in September, 1997, and a Hemoglobin Tutorial implemented with Jmol in July 2007.