Should you ever be stranded
on an alien planet
, be careful what you eat
! Even if none of the native edibles
contain deadly poisons
, you may develop serious nutritive deficiencies
regardless of how much you eat. You see, the protein in these organisms
(if there even is any) could be made up of D-amino acids, and/or amino acids that are not incorporated into terrestrial metabolism
*. Relying on these organisms as a food source could result in (eventually fatal) amino acid deficiency, which you might not recognize until it's too late.
* Chirality (somewhat simplified) is a property of molecules that are asymmetrical. A particular molecule can exist in a "right-handed" (D) form or "left-handed" (L) form. Ordinary chemical reactions create the two forms ("stereoisomers") in roughly equal amounts.
Essentially all amino acids found in terrestrial life forms are of the L-type. All amino acids found in proteins are L-type.This is because enzymatic reactions that occur in cells only produce this type.
In addition, all proteins are made up of only 20 different amino acids, with only a few modified forms present in some cases.