What determines the unique characteristics of each amino acid?

Each amino- acid contain carbon, hydrogen, nitrogen, and oxygen. All the amino- acids are mostly the same by structure because all contain a carbon atom in its center, an amine group, and a carboxyl group.

The unique characteristics that each amino acid has is determined by the R group(side chain) which is attached to its alpha carbon. The R group in each amino acid is different from others.  

The simplest amino acid is glycine which does not have any R group so it has a hydrogen atom in place of the R group. So side chain(R group) determines the unique characteristics of each amino acid.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.