D-(-) alanine molecule, ball and stick molecular model. The D-(-) alanine molecule is the mirror image of L-(+) alanine molecule - they are chiral enantiomers. Alanine is a? nonessential amino acid manufactured by the human body so, although found in a wide variety of foods particularly meats, it need not be obtained through diet. Black balls are carbon atoms, white balls are hydrogen atoms and the red ball is an oxygen atom and the blue ball is a nitrogen atom.