Question

Bond between phosphate and sugar in a nucleotide is

• A. H-bond
• B. Covalent bond
• C. Phosphodiester bond
• D. Sulphide bond

Answer 1

The correct option is B Covalent bond

The monomeric units of nucleic acids are called nucleotides. Nucleic acids are, therefore, called polynucleotides. Nucleotides are made up of three components:

1. A base that has a nitrogen atom (nitrogenous base)

2. A five carbon sugar

3. An ion of phosphoric acid. The two major purine bases are adenine and guanine and the three major pyrimidine bases are cytosine,
uracil and thymine.

Naturally ocurring nucleic acids have two types of pentose sugars : Ribose and Deoxyribose sugar. All known sugars in nucleic acids have the D-stereoisomeric configuration. Ribose sugar is found in RNA whereas deoxyribose sugar in DNA. Sugar and nitrogenous base join to form nucleoside. The bond between sugar and the base is called the
glycosidic bond. The base is free to rotate around the glycosidic bond.

The nucleotides are phosphoric acid esters of nucleosides with phosphate at position C5'. The nucleotide can have one, two or three phosphate groups designated as $\alpha$, $\beta$ and $\gamma$ for the first, second and third respectively. Therefore, the bond between sugar and phosphate is phosphoester bond which is a covalent bond.