Histidine: Abbreviated as His or H; one of the 20 amino acidsplugin-autotooltip__default plugin-autotooltip_bigAmino acid: molecules that are polymerized to form proteins. that are used to form proteinsplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes..