Question

The bond formed between phosphate and pentose sugars of DNA is

• A. Sulphide bond
• B. Phosphodiester bond
• C. Hydrogen bond
• D. Covalent bond

Answer 1

Answer: (B)

Phosphodiester bond

DNA is a polymer of nucleotides each of which has a pentose sugar, a nitrogenous base and phosphate group. The base of a nucleotide is joined covalently (at N-1 of pyrimidines and N-9 of purines) in an N –$\beta$- glycosyl bond to the 1’ carbon of sugar. The phosphate is linked by a phosphodiester linkage to the 5’ carbon. Two complementary bases of two strands of DNA are paired by hydrogen bonding; adenine makes two hydrogen bonds with thymine and guanine makes three hydrogen bonds with cytosine. Two successive nucleotides of DNA are joined by phosphodiester linkage in which the 5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide. Thus, phosphate and pentose sugars of DNA are joined by phosphodiester linkage; the correct answer is B.