The DNA double helix is composed of how many strands?

The DNA double helix is composed of how many strands?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (B)

DNA is organized as two long polynucleotide strands that wind around each other to form a double helix. These two strands run in opposite directions (antiparallel) and are held together by hydrogen bonds between complementary bases—adenine pairs with thymine, and cytosine pairs with guanine. This pairing creates the stable, familiar helix structure. Because the defining feature is this two-strand arrangement, DNA is not a single strand, nor does it involve three or four strands in its typical form. A single strand exists as single-stranded DNA, and extra strands would produce different structures rather than the canonical double helix.

DNA is organized as two long polynucleotide strands that wind around each other to form a double helix. These two strands run in opposite directions (antiparallel) and are held together by hydrogen bonds between complementary bases—adenine pairs with thymine, and cytosine pairs with guanine. This pairing creates the stable, familiar helix structure.

Because the defining feature is this two-strand arrangement, DNA is not a single strand, nor does it involve three or four strands in its typical form. A single strand exists as single-stranded DNA, and extra strands would produce different structures rather than the canonical double helix.