Question

In class, we learned that the two strands of a double helix have a constant distance between them. What single feature of the structure of a DNA molecule is most important for insuring that this is true?

a. only one phosphate unit is found in a nucleotide, rather than three. b. DNA contains thymine rather than uracil.
c. the two sides are antiparallel.
d. a purine always pairs with a pyrimidine and vice-versa.
e. the sides or stands are wound in a double helix configuration.

Answer 1

To maintain a constant distance between the two strands of a DNA double helix, it is most important that a purine always pairs with a pyrimidine. This pairing follows the specific A-T and C-G matchings, which keeps the width of the helix uniform.

Step-by-step explanation:

The single feature of the structure of a DNA molecule that is most important for ensuring that the two strands of a double helix have a constant distance between them is d. a purine always pairs with a pyrimidine and vice-versa. This principle ensures the uniform width of the DNA helix as the pairing of a purine (adenine or guanine) with a pyrimidine (cytosine or thymine) allows for a consistent arrangement of hydrogen bonds and molecular structure across the entirety of the DNA molecule. The pairings are A-T (adenine-thymine) and C-G (cytosine-guanine) with two and three hydrogen bonds respectively, helping to stabilize the double helix structure.