Nucleic acid fundamentals: what do the N-glycosidic bonds in DNA and RNA actually connect and how do they behave? Choose the most accurate statement about the glycosidic linkage in nucleotides (ribose/deoxyribose to the base).

Introduction / Context:
Nucleic acids are polymers built from nucleotides. Each nucleotide contains a base linked to a (deoxy)ribose sugar and at least one phosphate. The bond that connects the base to the sugar is the N-glycosidic bond. Understanding this bond clarifies how nucleotide structure, base orientation, and overall DNA/RNA stability arise.

Given Data / Assumptions:

• The question asks specifically about the N-glycosidic linkage in DNA and RNA.
• Backbone linkages (phosphodiester bonds) are separate from the glycosidic bond.
• Watson–Crick pairing occurs between complementary bases across strands, not via the glycosidic bond.

Concept / Approach:
The N-glycosidic bond forms between the anomeric carbon (C1′) of the sugar and a ring nitrogen of the base (N1 for pyrimidines; N9 for purines). This bond defines base orientation (anti/syn) but is distinct from the phosphodiester backbone and from the interstrand hydrogen bonds. It is relatively stable in base and more labile under acidic conditions (depurination).

Step-by-Step Solution:
Identify what is being linked: C1′ of sugar to a base nitrogen → N-glycosidic bond.Separate concepts: phosphodiester bonds link sugar–phosphate–sugar; glycosidic bonds do not.Assess stability: alkaline conditions attack RNA phosphodiester bonds (due to 2′-OH), not primarily the glycosidic bond; acid promotes depurination.Assess rotation: anti/syn conformations exist, but rotation is restricted by sterics and stacking; it is not freely rotatable 180° without consequence.

Verification / Alternative check:
Standard nucleic acid textbooks diagram the N-glycosidic link as sugar C1′–N9 (purines) or C1′–N1 (pyrimidines). Backbone linkages are shown separately as 3′–5′ phosphodiesters.

Why Other Options Are Wrong:
Hydroxide mainly promotes RNA backbone cleavage, not routine glycosidic hydrolysis. The glycosidic bond does not form or stabilize interstrand hydrogen bonds. Rotation is conformationally constrained, not freely 180°. Phosphate–sugar linkage is the phosphodiester, not the glycosidic bond.

Common Pitfalls:
Confusing glycosidic (base–sugar) with phosphodiester (sugar–phosphate–sugar) and assuming base-induced hydrolysis targets the glycosidic bond.

Final Answer:
Connect the sugar to the base.