Non-covalent interactions contribute to the 3D shapes and structures of RNA molecules. Which statement best describes this contribution?

• A. Covalent bonds along the backbone stabilize folding.
• B. Non-covalent hydrogen bonding between complementary base pairs drives RNA folding.
• C. Disulfide bonds stabilize RNA's 3D structure.
• D. Ionic bonds between phosphate groups determine secondary structure.

Answer: (B)

RNA folding is driven mainly by non-covalent interactions, with hydrogen bonding between complementary bases playing the central role. These hydrogen bonds between A–U and G–C (and occasional G–U) form base pairs that create stems and other secondary structures, bringing distant parts of the molecule into proximity and shaping the overall 3D form. While the covalent backbone bonds hold the chain together, they don’t drive folding in the same way; disulfide bonds aren’t a feature of typical RNA structure, and although metal ions and electrostatics influence stability, there aren’t ionic bonds between phosphate groups that determine the secondary structure. So, the non-covalent hydrogen bonding between bases is the best description of how RNA’s 3D shape is stabilized.