What is the backbone of DNA made of and what is the role of sugar-phosphate backbone?

• A. Deoxyribose sugar and phosphate groups linked by phosphodiester bonds; backbone provides structural support and orientation for bases.
• B. Ribose sugar and phosphate; stores genetic information.
• C. Amino acids forming peptide chain; stores energy.
• D. Nucleotides connected by glycosidic bonds; functions in catalysis.

Answer: (A)

The backbone of DNA is a sugar-phosphate framework built from deoxyribose sugars linked to phosphate groups by phosphodiester bonds. This framework provides the structural scaffold that holds the nucleotide units together and positions the bases in the inside of the molecule. The sugar-phosphate backbone also defines the molecule’s directionality from 5′ to 3′, which is essential for processes like replication and transcription. The phosphate groups give the backbone a negative charge, helping with interactions with proteins and aiding the overall stability and packaging of DNA. The other descriptions mix in the sugar of RNA (ribose), refer to proteins, or mention bonds that don’t connect successive nucleotides, so they don’t describe DNA’s actual backbone.