Point A if we examine any DNA molecule, the DNA molecule consists of two individual strands of nucleic acid. So we have two polynucleotide chains in a single DNA molecules and these two chains essentially run in an antiparallel fashion and they wind around a common access. And this can be described by the following diagram. So this is one strand, this is the five end of the strand and this is the three end of the strand and it runs along our common axis in the following direction from the top to the bottom. The second polynucleotide chain is this chain here and it runs in the opposite direction. So it essentially winds around the comet axis and it runs from the bottom to the top.