Usually ribonucleic acid (RNA) is single stranded and made up of long, unbranched polynucleotide chain.
The polynucleotide chain is formed by joining of ribonucleotides, with the help of 3’ – 5’ phosphodiester bonds in the same fashion as in case of DNA. But RNA is more stable than DNA because of intermolecular pairing.
Ribonucleotides = Pentose sugar (ribose) + N-base + phosphate group
Nitrogen bases are of two types
- Purines
- Adenine (A)
- Guanine (G)
- Pyrimidines
- Cytosine (C)
- Uracil (U)
Many RNAs possess number of minor bases in addition to above four bases, so there are unusual nucleotides like pseudouridine, inosine, dihydroxyuridine etc.
Following table summarizes N – bases, ribonucleosides and ribonucleotides.
| N – base | Ribonucleoside | Ribonucleotide | Abbreviation |
|---|---|---|---|
| Adenine | Adenosine | Adenosine monophosphate (Adenylic acid) | AMP |
| Guanine | Guanosine | Guanosine monophosphate (Guanylic acid ) |
GMP |
| Cytosine | Cytidine | Cytidine monophosphate (Cytidylic acid) |
CMP |
| Uracil | Uridine | Uridine monophosphate (Uridylic acid) |
UMP |
Only difference between DNA and RNA chemical composition is RNA has ribose sugar, has hydroxyl group (- OH) at the 2’ position and N-base thymine is replaced by uracil.
As we have seen generally RNA is single stranded and does not form DNA like double helical structure. Though it is the case, when certain parts of RNA polynucleotide chain have antiparallel complementary segments, they join to form double helix.
Visit page DNA chemical composition.