RNA molecules are made up of three chemical components. These are-
1. Nitrogen Alkali: This alkali is formed by carbon, hydrogen, oxygen and nitrogen. Alkaline compounds form rings. Based on the number of rings, nitrogenous bases can be divided into two groups.
(i) Purines: Dicyclic nitrogenous bases are called purines. Its common symbol is C5H4N4. It is composed of adenine and guanine.
(ii) Pyrimidine: A cyclic nitrogenous base is called pyrimidine. Its common symbol is C4H4N2. It is composed of cytosine and uracil.
2. Pentose sugars: Five carbon sugars are called pentose sugars. RNA molecules contain the ribose sugar. It is a type of monosaccharide. Ribose sugar is so named because it has a hydroxyl group at the 2nd carbon.
3. Phosphoric acid: One of the chemical components of RNA molecules is phosphoric acid. Its molecular symbol is H3PO4. It contains one divalent oxygen atom and three monovalent hydroxyl groups. Oxygen and hydroxyl groups combine with a pentavalent phosphorus atom to form phosphoric acid.
A molecule of pentose sugar and a molecule of nitrogen base combine to form a molecule of nucleoside. Again, one molecule of phosphate joins with one molecule of nucleoside to form one molecule of nucleotide. The smallest RNA molecule can contain 22 and the largest RNA molecule can contain 10,000 nucleotides.