Watson's DNA model is :
Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds.This common form of DNA is said to be right handed because as one looks down the double helix, the base residues form a spiral in a clockwise direction.These two strands run in opposite directions to each other and are therefore anti-parallel.
Right handed, parallel
Left handed, anti parallel
Left handed, parallel
Right handed, anti parallel