"You exist because we allow it, and you will end because we demand it."
Mass Effect fan
Mass Effect fan - Normandy
- Mass Effect series fan
Levo vs Dextro:
molecules based on carbon atoms can have up to four atoms attached to a central carbon. If you imagine this as a tetrahedron (d4, if you're a tabletop gamer) then you'll notice that you can actually arrange those four atoms in two different ways that cannot be reconciled by rotating the molecule. If they're arranged one way, it's (arbitrarily) named a levo- or left-handed molecule. If it's arranged the other way, it's a dextro- (right handed) molecule.
Enzymes are built to attach to specific molecular geometries, and if they don't match the molecule, they don't work. So imagine if you will an enzyme that is designed to break a protein down into its constituent amino acids, so they can be re-used to build bodily proteins. This protease is shaped to grab onto L-amino acids and ignore everything else. When confronted by a D-amino acid, it quite simply won't grab on, which means the protein doesn't get digested, and is quite useless to the organism.
Out of the major food molecules, protein and carbohydrates exhibit chirality, fats do in triglyceride (but not free fatty acid) form. Minor food molecules such as volatile flavor compounds and vitamins vary based on the particular molecules. Interestingly, ethanol is non-chiral, so Tali's need for Turian brandy is a curious case, and is either a case of the writers not being biochemists, or the possibility that Quarians and Turians do not have ethanol dehydrogenase, an enzyme to break down ethanol, and instead rely on some other form of alcohol for intoxication.