Question

A unit composed of a sugar and base linked by R glycosidic bond is known as a __________.

• A. Nucleotide
• B. Nucleoside
• C. Glycoside
• D. Purine

Answer 1

The correct option is B Nucleoside

The nitrogen base such as purines or pyrimidines bind with the 1st carbon of the sugar molecule (ribose in case of RNA and deoxy-ribose incase of DNA molecules) by forming a glycosidic bond. Then it is called as 'Nucleoside'.

The glycosidic bond is a covalent bond forms by the condensation reaction and by removal of the water molecule.

While in the nucleotides, the tri-phosphate group will be attached to the 5th carbon atom of sugar molecule on the other end in a nucleoside.

The examples for ribo nucleosides are adenosine, cytosine while the ribo nucleotides are deoxy adenosine, deoxy cytosine.

The examples for deoxyribo nucleosides and nucleotides are deoxy adenosine and deoxy adenine.

Since ribonucleosides and ribonucleotides are uncommon, the deoxyribo nucleosides and nucleotides were called as adenosine and adenine instead of adding deoxy.