Give the salient features of the double helix structure of DNA.

The salient features of the double helix structure of DNA are as follows: A double-stranded DNA molecule has two polynucleotide chains. The two strands have antiparallel polarity, which means one chain has 5'-3' polarity and the other has 3'-5' polarity. Purines and pyrimidines form hydrogen bonds that bind the two strands of DNA. Adenine and Thymine are always two hydrogen bonds apart, while Guanine and Cytosine are always three hydrogen bonds apart. The two chains are coiled around each other with a 3.4 nm helix pitch and a 3.4 A° gap between base pairs. Sugars and phosphates form the backbone of the DNA double helix, with bases projecting inwards.

Draw a neat diagram to show the Watson-Crick model for semi-conservative DNA replication.

Figure: DNA double-helical structure DNA is a double-helical structure consisting of two long strands, coiled around a central axis. This structure was discovered by Watson and Crick. Each strand is a polynucleotide chain that is composed of many nucleotides. Each is formed by a nitrogenous base, deoxyribose sugar, a phosphate group, and one nitrogen base. Sugar and nitrogenous bases are connected by glycosidic bonds while sugar and phosphate are joined by a phosphodiester bond, known as phosphodiester linkage. There is a complementary pairing of purines and pyrimidines. Adenine, and thymine pair with hydrogen double bonds while cytosine and guanine pair with hydrogen triple bonds.