Question

Uridine present only in RNA is
A. Nucleoside
B. Purine
C. Pyrimidine
D. Nucleotide

Answer 1

Hint: Ribonucleic acid (RNA) is a polymeric molecule which is essential in various biological roles such as in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid (DNA) both are nucleic acid molecules. Along with proteins, lipids and carbohydrates, nucleic acids have one of the four major macromolecules essential for all known forms of life. Same as DNA, RNA is also assembled as a chain of nucleotides, but unlike DNA, RNA in nature is found as a single strand folded onto itself, rather than on a paired double strand.

Complete answer:
Each nucleotide of RNA is made up of a ribose sugar, with carbons numbered 1' through 5' and a nitrogenous base which is attached to the 1' position, in general, adenine (A), cytosine (C), guanine (G), or uracil (U). Among them Adenine and guanine are purines, whereas cytosine and uracil are pyrimidines. A phosphate group is also attached to the 3' position of one ribose and the 5' position of the next ribose.
The phosphate groups have a negative charge which makes each RNA a charged molecule (polyanion). The bases form hydrogen bonds between purine and pyrimidine e.g. cytosine and guanine,and between adenine and uracil.
Nucleosides are defined as the structural subunit of nucleic acids such as DNA and RNA. A nucleoside is composed of a nucleobase which is either a pyrimidine (cytosine, thymine or uracil) or a purine (adenine or guanine) and a five carbon sugar which is either ribose in case of RNA or deoxyribose in case of DNA.
A nucleotide consists of a sugar molecule (either ribose in RNA or deoxyribose in DNA) attached to a phosphate group and a nitrogen-containing base.
Purines are heterocyclic aromatic organic compounds made up of two rings fused together, it is water-soluble. These are the most widely occurring nitrogen-containing heterocycles in nature.
Pyrimidines are aromatic heterocyclic organic compounds similar to pyridine. In nucleic acids, there are three types of nucleobases that are pyrimidine derivatives: cytosine, thymine, and uracil.
When a nitrogenous base is linked to the ribose sugar through N- glycosidic linkage to form a nucleoside such as adenosine, guanosine, cytidine, uridine.

So the correct answer is option A.nucleoside.

Note:
In a nucleoside, the anomeric carbon is linked with the help of a glycosidic bond to the N9 of a purine or the N1 of a pyrimidine. Examples of nucleosides include cytidine, an alcohol group (-CH2-OH) to produce nucleotides. Nucleotides are also called the molecular building-blocks of DNA and RNA technology. In medicine various nucleoside analogues are used as antiviral or anticancer agents.