Why there are only levo amino acids in the chemical composition of the living organisms

In the structure of the DNA-histone system there are three kinds of elements which present spatial asymmetries: a) the D-deoxyribose molecules; b) the two strands of DNA which are wound counter-clockwise around the helical axis; c) the levo amino acids of the histones. This paper presents data and arguments which demonstrate that all these spatial asymmetries are interdependent and compose a unique system.