DNA is Deoxyribose nucleic acid. It occurs in chromosomes (nuclear reticulum). DNA has deoxyribose with one less oxygen atom in its molecule. DNA is double stranded molecule. Biologists are of view that all secrets of life are embodied in DNA or in other words it is the chemical basis of life. DNA is sole genetic (hereditary) material migrating intact from generation to generation through reproductive units or gametes and is responsible for the development of specific characters of a plant. It also controls the biosynthetic processes of the cell including protein synthesis, Watson and Crick gave model of DNA in 1953 which double stranded structure. Each strand (helix) is a chain of several nucleotides and is known as poly nucleotide chain. Each nucleotide consist of a de oxyribose sugar, one nitrogen base and one molecule of phosphoric acid. Nitrogen bases are adenine, guanine, cytosine and thiamine.
Dicyclic nitrogen bases are purines, therefore adnine and guanine are purines. Monocyclic nitrogen bases like cytosine and thiamine are known as Pyramidines.
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