the structure of dna and rna

         DNA controls heredity on molecular level:

• it is a self-replicating molecule capable of passing genetic information from one generation to the next;

• it contains in its base sequence the genetic code used to synthesis proteins.

        DNA is built up from units called nucleotides. each strand of DNA is made by the condensation polymerization of these monomer nucleotides. nucleotides are themselves made from three components:

• a sugar;

• a phosphate;

• a nitrogen-containing organic base.

        A DNA molecule consists of two strands. each strand of DNA is a condensation polymer of sugar molecules and phosphate groups, that forms sugar-phosphate backbone. the phosphate group links the 5` carbon atom of one nucleotide with 3` carbon atom of the next. the phosphate group is involved in two ester bonds with –OH groups on the sugars. this linkage is referred to as a phosphodiester link.

        Various forms of RNA are involved in the processes of “gene expression” that result in the production of proteins. The nucleotides in RNA are also formed from a sugar, a phosphate group and a nitrogen-containing base.

• in RNA the sugar is ribose

• in RNA molecule the phosphate group is again attached to the 5` carbon of the sugar

• RNA contains four nitrogen-containing bases: adenine, guanine, uracil and cytosine. in RNA uracil replace thymine.

          The individual strands of RNA are very similar to DNA strands in the that they both contain a sugar-phosphate backbone, with nitrogen-containing bases attached to the sugar molecules. RNA molecules are polynucleotides containing ribose as the sugar component rather than deoxyribose.