In a DNA molecule, two antiparallel strands that are complementary in their nucleotide sequence are paired to form a
In a DNA molecule, two antiparallel strands that are complementary in their nucleotide sequence are paired to form a
Select an option to attempt
Correct Answer: Option D
Explanation
Watson-Crick B-form DNA double helix parameters (derived from X-ray crystallography by Franklin, Watson, Crick, Wilkins, 1953): Handedness: RIGHT-HANDED helix (the helix coils clockwise when viewed from either end). Helical repeat: 10.5 bp per complete 360° turn (commonly approximated as 10 bp/turn for calculations). Pitch: 35.7 Å (~34 Å with the 10 bp/turn approximation). Rise per base pair: 3.4 Å. Diameter: ~20 Å. Base pairs are anti-parallel (5'→3' on one strand, 3'→5' on the other). Major groove (~22 Å wide) and minor groove (~12 Å wide). Z-form DNA is left-handed; A-form DNA is right-handed but more compact (11 bp/turn). Answer: right-handed double helix with approximately 10 nucleotide pairs per helical turn.