What kind of isomers can amino acids form? Which isomer is present in most living organisms?

Question

don't major compounds of living organisms consist of modifications of hydrocarbons

Although D amino acids can be found in nature, only the L isomers are used to form proteins. The D isomers are most often found attached to the cell walls of bacteria and in antibiotics that attack bacteria. The presence of these D isomers protects the bacteria from enzymes the host organism uses to protect itself from bacterial infection by hydrolyzing the proteins in the bacterial cell wall.
Source:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/1biochem/amino2.html