Structure of nucleic acid- Nucleotide, the building block of nucleic acid consists of pentose sugar, base and phosphoric acid residue. Nucleotides are connected by a covalent linkage between pentose sugar of nucleotide and phosphoric acid of the next nucleotide (Figure 38.2). There are 5 different types of nucleobase (cytosine, uracil, thymine, adenine and guanine) attached to the sugar through a N-glycosidic linkage. Uracil is found in RNA whereas thymine is present in the DNA. These nucleotide are abbreviated with the first letter of the base to write the nucleotide sequence of the nucleic acid, such as adenine is denoted as “A”. The bases have a specificity towards the other base to form a pair through hydrogen bonding, “A” is making 2 hydrogen bonding to the “T” where as “G” is making 3 hydrogen bonding to the “C”. DNA is a double helix structure with the bases present on the both starnd and sequence information on one strand of DNA can determine the sequence of the other strand.

Figure 38.2: The structure of nucleic acid.