DNA stands for Deoxy Ribo Nucleic Acid. It is an organic chemical of complex molecular structure that is found in all prokaryotic and eukaryotic cells and in many viruses. DNA codes genetic information for the transmission of inherited traits.They are found inside every cell.Cell has nucleus which has a nuclear membrane, chromosome, nucleoplasm,nucleolus.Chromosome consists of strings of DNA.

Discovery of DNA:

James Dewey Watson (born April 6, 1928) is an American molecular biologist, geneticist and zoologist.

Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was a British molecular biologist, biophysicist, and neuroscientist.These two scientists,Watson &Crick in 1953 designed the structure for DNA as double helix which they realised could carry biological information and was awarded Nobel prize in 1962.

Structure of DNA:

There are three classes of macromolecules: proteins, lipids, and carbohydrates. There is a fourth class of macromolecules: nucleic acids. Like other macromolecules, nucleic acids are composed of monomers, called nucleotides, which are polymerized to form large strands. Each nucleic acid strand contains certain nucleotides that appear in a certain order within the strand, called its base sequence. The base sequence of deoxyribonucleic acid (DNA) is responsible for carrying and retaining the hereditary information in a cell. The building blocks of nucleic acids are nucleotides. Nucleotides that compose DNA are called deoxyribonucleotides. The three components of a deoxyribonucleotide are a five-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base, a nitrogen-containing ring structure that is responsible for complementary base pairing between nucleic acid strands. The deoxyribonucleotide is named according to the nitrogenous bases. The nitrogenous bases adenine (A) and guanine (G) are the purines; they have a double-ring structure with a six-carbon ring fused to a five-carbon ring. The pyrimidines, cytosine (C) and thymine (T), are smaller nitrogenous bases that have only a six-carbon ring structure.