DNA Backbone Bond Identification

Steps:

• DNA consists of nucleotides with deoxyribose sugar, phosphate, and bases.
• In a single strand, nucleotides link via the sugar-phosphate backbone.
• The bond between the 3' carbon of one sugar and the 5' phosphate of the next is a phosphodiester linkage.
• Label X indicates this inter-nucleotide connection in the strand.

Why D is correct:

• Phosphodiester bonds form the DNA backbone by esterifying phosphoric acid with hydroxyl groups on adjacent sugars, as defined in nucleic acid structure.

Why the others are wrong:

• A. Glycosidic bonds link nitrogenous bases to deoxyribose sugars, not the backbone.
• B. Hydrogen bonds connect complementary bases between DNA strands, not within one strand.
• C. Peptide bonds join amino acids in proteins, absent in DNA.

Final answer: D