DNA has an antiparallel double helix.

DNA has an antiparallel double helix.

• A. Antiparallel double helix
• B. Parallel double helix
• C. Single-stranded helix
• D. Triple helix

Answer: (A)

DNA features two long strands that run in opposite directions and twist into a right-handed helix. This antiparallel arrangement means one strand goes 5' to 3' while the other goes 3' to 5'. That orientation is essential for accurate base pairing and for how enzymes interact with DNA during replication and transcription, since polymerases add nucleotides to the 3' end and read templates accordingly. The description that matches this is an antiparallel double helix. A parallel double helix would place the strands in the same direction and isn’t how DNA is structured in cells; a single-stranded helix lacks a complementary partner; a triple helix involves three strands and isn’t the usual form of DNA.

DNA features two long strands that run in opposite directions and twist into a right-handed helix. This antiparallel arrangement means one strand goes 5' to 3' while the other goes 3' to 5'. That orientation is essential for accurate base pairing and for how enzymes interact with DNA during replication and transcription, since polymerases add nucleotides to the 3' end and read templates accordingly. The description that matches this is an antiparallel double helix. A parallel double helix would place the strands in the same direction and isn’t how DNA is structured in cells; a single-stranded helix lacks a complementary partner; a triple helix involves three strands and isn’t the usual form of DNA.