Which component forms the backbone of both DNA and RNA?

• A. Ribose
• B. Phosphate group
• C. Guanine
• D. Amino group

Answer: (B)

The backbone of both DNA and RNA is the sugar-phosphate chain that runs along the length of the molecule. Phosphate groups form phosphodiester bonds that link the 5' phosphate of one nucleotide to the 3' hydroxyl of the next, creating a continuous, repeating framework. This sugar-phosphate backbone provides the structural scaffold to which the nitrogenous bases attach and pair, enabling the genetic information to be stored and read. While the sugar component (ribose in RNA, deoxyribose in DNA) is part of the backbone, the phosphate linkages are the essential connectors that hold the polymer together. The bases themselves and any amino group are not part of this backbone structure.