Question

In nucleoside, the nitrogen base is attached in pentose sugar at
a. Carbon-5’- of a pentose sugar
b. Carbon-1' of a pentose sugar
c. N 1 and N 9
d. Both Band C

Answer 1

Nucleosides are glycosylamines, and they are considered as nucleotide if they have phosphate attach to it, because the major difference between nucleoside and nucleotide is, in both of them have a nitrogen base with pentose sugar, and in nucleotide extra phosphate is attached, but it is absent in nucleoside, and this are basic units of the nucleic acids.

Complete answer:
- Both nucleoside and nucleotides are building blocks of nucleic acids.
- A nucleoside consists of a nucleobase and five-carbon sugar.
- Whereas nucleotide consists of nucleobase and five-carbon sugar, and a phosphate compound.
- In the nucleoside, the anomeric carbon is linked to the glycosidic bond of N9 of the purine, or to the N1 of the pyrimidine.
- Some of the examples of the nucleosides are cytidine, inosine, uridine, guanine, thymidine, and adenosine.
- As we know that nucleoside consists of nucleobase and the 5 carbon sugar, whereas nucleoside can be phosphorylated by the enzyme kinases inside the cell, at the sugar primary alcohol group. So because of this phosphorylation, nucleosides are converted to nucleotides, and these are the building blocks of both DNA and RNA molecules.
- Nucleosides are produced from the nucleotides in the liver, but they are abundantly supplied through the ingestion and digestion of the nucleic acids present in the diet.

Hence, the correct answer is option (B).

Note: In the medicine, several nucleosides analogs are used as antiviral and anticancer agents, where these nucleosides are incorporated into the cells, and they are activated by converting to nucleotides. They administer the nucleosides instead of nucleotides because these nucleotides cannot cross the cell membranes.