What is the native form of DNA consisting of two adjacent polynucleotide strands wound into a spiral?

What is the native form of DNA consisting of two adjacent polynucleotide strands wound into a spiral?

• A. Double helix
• B. Single helix
• C. Nucleotide
• D. Purines

Answer: (A)

DNA's natural form is a double helix: two polynucleotide strands run alongside each other and twist into a spiral. These strands are antiparallel, with the sugar–phosphate backbones on the outside and the bases paired inside through hydrogen bonds (A with T, C with G). This arrangement, along with base stacking, stabilizes the molecule and creates the characteristic grooves that proteins recognize. The term double helix specifically describes two strands wound together, whereas a single helix would mean only one strand, a nucleotide is a single building block, and purines are a class of bases, not a structural form.

DNA's natural form is a double helix: two polynucleotide strands run alongside each other and twist into a spiral. These strands are antiparallel, with the sugar–phosphate backbones on the outside and the bases paired inside through hydrogen bonds (A with T, C with G). This arrangement, along with base stacking, stabilizes the molecule and creates the characteristic grooves that proteins recognize. The term double helix specifically describes two strands wound together, whereas a single helix would mean only one strand, a nucleotide is a single building block, and purines are a class of bases, not a structural form.