- A DNA is a macromolecule formed of several thousand units or monomers. These monomers are called nucleotides.
- A nucleotide is formed of one molecule of deoxyribose sugar, one molecule of phosphoric acid and one of the four nitrogenous bases.
- A DNA contains following characters:
- DNA molecule consists of two parallel chains of polynucleotides forming a double helical structure.
- Both the strands are spirally coiled.
- The two strands are antiparallel.
- These helical strands have sugar-phosphate chain on the outside and purines and pyrimidine bases on the inner side of the helix.
- Both the strands are joined together by weak hydrogen bonds.
- The distance between two strands is 20A0.
- There are 10 pairs on a complete turn (34A0). The distance between two base pairs is 3.4 A0.
- A purine base is attached to its specific base. i.e. Adenin(A) attaches to Thymine(T) by two hydrogen bonds , cytosine( C) to Guanine(G) by three hydrogen bonds.
- A DNA molecule contains 28% adenine, 24% Guanine, 20% cytosine and 28% thymine.
- Nucleotides in a helix are joined together by Phosphodiester bonds.
It was discovered by Friedrich Miescher in 1869.
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