. Describe DNA as proposed by Watson and Crick?
According to Watson and Crick, DNA has a double helical structure in which each helical turn has about 10 nucleotides.
The nucleotide consists of Deoxyribose (a pentose sugar) and a phosphate group which forms the backbone of each strand. DNA molecule has two types of nitrogen bases which are purine and pyrimidine. Purine in turn consists of Adenine (A) and Thyamine (T), while pyrimidine consists of Cytosine(C) and Guanine(G) as. Also adenine pairs only with thyamine and cytosine pairs only with guanine. Thus one of them is called the base strand and other is called the complementary strand. It is the weak hydrogen bond that holds the nitrogen bases together.