evolutionary speaking,why are ALL sugars in D-form and ALL amino acids in L form in biological systems?

Answer 1

No they are not.
Here is a good website:
http://www.shs.springfield.k12.il.us/academics/departm..
alpha.delta.edu/cmurbano/bio171/Unit%201/05Macr..
http://dl.clackamas.edu/ch106-10/glucose.htm

Answer 2

Great question, probably one of the best I have seen on these forums. To the above answerer, one link doesn't work and the other has no relevence to the question. Unfortunetly we are pretty much stumped on this one for now, it has been in the minds of giants such as Linus Pauling and Francis Crick. The most recent and best theory I have seen put forward has a good grounding in experimentalism. Basically in the pre-biotic conditions biological homochirality evolved due to the ability of amino acids to autocatalyze reactions whereby the concentration of one particular chiral form of reaction product will predominate. At least this is the current thinking, it has yet to be conclusively demonstrated with only amino acids as reactants and products but seems very possible.