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From Proteopedia

Peptides are chains of amino acids linked by peptide bonds. Long peptides, or polypeptides, are called proteins.

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).