Life would not be possible if the amino acids in proteins did not have the same sense of handedness.  We call this homochirality.  All of the chiral amino acids in proteins have "L" handedness (after the latin levo, for left).  The same is true of the carbohydrates - all sugars are "D" (latin dextro, right).  What this means, why it matters, how it might have happened, and the relevance to extraterrestrial organics will be explained.  Fair warning:  You'll never look at nature the same way again.