Properties of Guanine Nucleotides

Steps:

• Statement 1: Nucleotides contain a nitrogenous base, sugar, and phosphate; guanine pairs with ribose in RNA or deoxyribose in DNA.
• Statement 2: In DNA/RNA, guanine (purine) base-pairs with cytosine (pyrimidine) using three hydrogen bonds.
• Statement 3: Purines have a double-ring structure; guanine fits this category alongside adenine.
• All statements hold true, confirming option A.

Why A is correct:

• Molecular biology defines nucleotides with variable sugars (ribose/deoxyribose), guanine-cytosine pairing via three H-bonds, and guanine as a purine by its fused-ring formula.

Why the others are wrong:

• B omits statement 3, but guanine's double-ring structure classifies it as a purine.
• C omits statement 2, but guanine-cytosine pairing requires exactly three hydrogen bonds.
• D omits statement 1, but guanine nucleotides exist in both RNA (ribose) and DNA (deoxyribose).

Final answer: A