Nucleotides, the fundamental units of DNA and RNA, are composed of a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. Let's examine each assertion:
(A) Purines and pyrimidines are nitrogenous bases.
This statement is accurate. Adenine and guanine are purines, while cytosine, thymine, and uracil are pyrimidines, all functioning as nitrogenous bases.
(B) Nucleotides are non-enzymatic molecules.
This statement is incorrect. While not enzymes themselves, nucleotides serve crucial roles as energy carriers (e.g., ATP) and signaling molecules (e.g., cAMP).
(C) Phosphate group is linked to – OH of 5′ C of a nucleoside through phosphoester linkage.
This statement is accurate. The phosphate group covalently bonds to the 5' hydroxyl group of the sugar moiety in a nucleoside, forming a nucleotide via a phosphoester linkage.
(D) In RNA, every nucleotide residue has an additional – OH group present at 2′ position in the ribose.
This statement is accurate. Ribose in RNA possesses a hydroxyl group at the 2' carbon position, which is absent in DNA's deoxyribose.
(E) Thymine is an example of Pyrimidine.
This statement is accurate. Thymine is a pyrimidine base found in DNA.
Upon review, statements (B) and (E) were initially assessed incorrectly. Statement (E) is correct, while statement (B) is incorrect.
Therefore, the correct option is: (B) only