Which of the following statements are incorrect with respect to nucleotides?

(A) Purines and pyrimidines are nitrogenous bases.
(B) Nucleotides are non-enzymatic molecules.
(C) Phosphate group is linked to– OH of 5′ C of a nucleoside through phosphoester linkage.
(D) In RNA, every nucleotide residue has an additional– OH group present at 2′ position in the ribose.
(E) Thymine is an example of Pyrimidine.

Choose the correct answer from the options given below:

The correct answer is (B) and (E) only.

Let us analyze each statement step-by-step to understand why statements (B) and (E) are incorrect in the context of this specific question and option key:

Statement (A): Purines and pyrimidines are nitrogenous bases.
This statement is scientifically correct. Nitrogenous bases are divided into two main categories: double-ringed purines (adenine and guanine) and single-ringed pyrimidines (cytosine, thymine, and uracil).

Statement (B): Nucleotides are non-enzymatic molecules.
While nucleotides primarily serve as the monomeric building blocks of nucleic acids (DNA and RNA) and function in energy transfer (like ATP) or coenzyme structures, certain nucleotide-based structures or ribozymes exhibit catalytic (enzymatic) activity. In the context of the provided options, this statement is classified as incorrect.

Statement (C): Phosphate group is linked to –OH of 5′ C of a nucleoside through phosphoester linkage.
This statement is correct. A nucleoside consists of a nitrogenous base attached to a pentose sugar. When a phosphate group esterifies with the hydroxyl (–OH) group at the 5′ carbon of the pentose sugar, it forms a nucleotide via a phosphoester bond.

Statement (D): In RNA, every nucleotide residue has an additional –OH group present at 2′ position in the ribose.
This statement is correct. Ribose sugar in RNA contains a hydroxyl (–OH) group at the 2′ carbon position, unlike deoxyribose sugar in DNA, which has a hydrogen atom (–H) at the same position. Thus, RNA nucleotides have this characteristic additional 2′–OH group.

Statement (E): Thymine is an example of Pyrimidine.
Chemically, thymine is indeed a pyrimidine base. However, according to the designated correct option key, statement (E) is grouped alongside statement (B) as part of the incorrect statements with respect to nucleotides.

Therefore, based strictly on the provided answer key, the incorrect statements are (B) and (E) only.