RNA (Ribonucleic acid):

Ribonucleic acid or RNA is the second major nucleic acid in cells, serves as genetic messenger, passing the information stored in DNA to other parts of cell for protein synthesis. In some cases as retro-viruses RNA is found as genetic material. Like DNA it is also a long unbranched polymer consisting of nucleotides joined by phosphodiester bonds in 5' to 3' direction. RNA differs from DNA in two respects…

1) Uracil (U) is found in RNA in place of Thymine (T).

2) The sugar units in RNA are ribose rather than deoxyribose (in DNA).

In addition to 3' - 5', a 2' - 5' linkage is also possible for RNA. This 2' − 5' linkage is important in the removal of introns and joining of exons for the formation of mature RNA during RNA splicing. Due to the presence of an OH group at C-2 , RNA is hydrolysed more rapidly under alkaline conditions. This OH group is directly involved in the formation of 2',3'- monophosphate nucleotides which are further hydrolysed to yield a mixture of 2' and 3' nucleoside monophosphate. This may be the reason why DNA is employed for storing the genetic information and not RNA.

Wherever complimentary sequences are present in RNA, the predominant double stranded structure is an A form right handed double helix. Z form helices have been made in laboratory under very high salt concentration or high temperature conditions. B form of RNA has not been observed.

Due to unknown reasons, RNA duplexes are more stable than DNA duplexes. At neutral pH denaturation of a double helical RNA often requires a temperature 20°C or more than that for DNA.