Double-stranded DNA consists of two polynucleotide chains whose nitrogenous bases are connected by hydrogen bonds. Within this arrangement, each strand mirrors the other as a result of the anti-parallel orientation of the sugar-phosphate backbones, as well as the complementary nature of the A-T and C-G base pairing.

Why DNA is a double helix?

The double comes from the fact that the helix is made of two long strands of DNA that are intertwined—sort of like a twisted ladder. Each strand of DNA (or side of the ladder) is a long, linear molecule made up of a backbone of sugars and phosphate groups. Connected to each sugar is a nitrogenous base.

How does DNA become two strands?

The two strands of DNA in a double helix are held together by pairing between the nitrogenous bases in the nucleotides of each strand. ... Every adenine on one DNA strand forms two hydrogen bonds with a thymine molecule on the complementary strand and vice versa.