Identify the statements which do not hold true for Deoxyribose Nucleic Acid.
A. Only purine bases are present in DNA.
B. Deoxyribose sugar is present
C. A nitrogenous base is linked to the 1'C pentose sugar through N-glycosidic linkage.
D. Phosphate group is linked to OH of 4'C of a nucleotide.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A and D only
A. Only purine bases are present in DNA. — False. DNA has both purines (adenine, guanine) and pyrimidines (cytosine, thymine); a purine always pairs with a pyrimidine.
B. Deoxyribose sugar is present — True. The sugar of DNA is 2'-deoxyribose.
C. A nitrogenous base is linked to the 1'C pentose sugar through N-glycosidic linkage. — True. Base + sugar joined this way form a nucleoside.
D. Phosphate group is linked to OH of 4'C of a nucleotide. — False. The phosphate is linked to the OH of the 5' carbon by a phosphoester linkage.
NCERT Extract:
Structure of Polynucleotide Chain – “… When a phosphate group is linked to OH of 5’ C of a nucleoside through phosphoester linkage, a corresponding nucleotide (or deoxynucleotide depending upon the type of sugar present) is formed. Two nucleotides are linked through 3’-5’ phosphodiester linkage to form a dinucleotide.”
Structure of Polynucleotide Chain – “… There are two types of nitrogenous bases – Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine). Cytosine is common for both DNA and RNA and Thymine is present in DNA. Uracil is present in RNA at the place of Thymine.”