CPK Color Scheme

This is the backbone of 1 amino acid (AA).

Here is the backbone of a tripeptide (3 AA's). No side groups are shown, and most hydrogens are omitted.

Now each AA has a 1-carbon side group, so we have Ala Ala Ala (tri-alanine)

Adding an NH3 to a carbon chain on the 1st AA gives Lys Ala Ala

Adding three more carbons to the 3rd AA gives isoleucine: Lys Ala Ile

The 4th AA is threonine with its hydroxyl, giving Lys Ala Ile Thr

Here is the shape of the tetrapeptide.

The stick representation has too much detail for larger proteins, so the alpha-carbons are connected with a line called the BACKBONE trace.

Showing only the backbone makes it easier to see the secondary and tertiary structure of a protein.