DNA( Deoxyribo Nucleic Acid)
DNA is mainly found in the nucleus. A small amount is laso found in mitochondria and chloroplasts. It is a macromolecule formed by the end to end polymerisation of a large number of repeated units called deoxyribonucleiotides or simply nucleotides.
Wattson and Crick established the structure of DNA moleculein 1953 on the basis of the x-ray diffraction. For this excellent discovery, Wattson and Crick was awarded with Nobel Prize in 1962. According to them, DNA is composed of two antiparallel polynucleotide chains that form a double helix around the central axis.
The strands are made up of alternate bands of deoxyribose sugar and phospate molecules. They are joined by the phospdiester linkages.
Each deoxyribo sugar in the strand has one N-base horizonatally attached to it at carbon-1. The four N-bases can occur in any possible sequence along the length of a strand. The N-base + deoxyribose sugar + phosphate together form one unit or deoxyribonucleotide in the strand. Such many deoxyribonucleotides are linked with each other in a linear fashion, therefore, the ruslting strand is described as the polynucleotide strand and DNA moelucle as polynucleotide molecule.
