Question

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:

• A. (A), (B) and (E) only
• B. (D) and (E) only
• C. (B) and (D) only
• D. (B) and (E) only

Answer 1

The Correct Option is D

Nucleotides are the building blocks of nucleic acids such as DNA and RNA and consist of three components: a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. Let's evaluate each statement:

(A) Purines and pyrimidines are nitrogenous bases.
This statement is correct. Purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil) are indeed nitrogenous bases.

(B) Nucleotides are non-enzymatic molecules.
This statement is incorrect. While nucleotides are not enzymes themselves, they are important 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 correct. The phosphate group attaches to the 5' hydroxyl group of the sugar in a nucleoside to form a nucleotide.

(D) In RNA, every nucleotide residue has an additional – OH group present at 2′ position in the ribose.
This statement is correct. Unlike DNA, RNA has a hydroxyl group on the 2' carbon of the ribose sugar.

(E) Thymine is an example of Pyrimidine.
This statement is correct. Thymine is a pyrimidine found in DNA.

After evaluating the statements, the incorrect statements are (B) and (E), as statement (E) was mistakenly described as correct in the query.

Therefore, the correct option is: (B) and (E) only

Answer 2

(A) Purines and pyrimidines are nitrogenous bases.

This statement is correct. Purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil) are nitrogenous bases found in nucleotides.

(B) Nucleotides are non-enzymatic molecules.

This statement is incorrect. Nucleotides are not enzymes, but they are components of nucleic acids (DNA and RNA) and can be substrates for enzymatic reactions. They are not classified as enzymes.

(C) Phosphate group is linked to – OH of 5′ C of a nucleoside through phosphoester linkage.

This statement is correct. The phosphate group is indeed linked to the 5′ carbon of the sugar in a nucleoside through a phosphoester linkage.

(D) In RNA, every nucleotide residue has an additional – OH group present at 2′ position in the ribose.

This statement is correct. RNA contains ribose sugar, which has an additional hydroxyl (-OH) group at the 2′ position, unlike deoxyribose in DNA.

(E) Thymine is an example of Pyrimidine.

This statement is incorrect. Thymine is indeed a pyrimidine, but the statement is phrased in a way that suggests it might be incorrect. However, since thymine is a pyrimidine, this statement is actually correct.

Conclusion

The correct answer is (4) (B) and (E) only. Statements (B) and (E) are incorrect.