Question

Which is an incorrect statement concerning the DNA double helix?

Select one:

a. The sugar-phosphate backbone is on the outside of the helix and the base pairs are on the inside.

b. Hydrogen bonding holds together the two strands.

c. The two strands are identical but proceed in opposite directions.

d. Only purine-pyrimidine base pairs can be accommodated.

Answer 1

answer : c) The two strands are identical but proceed in opposite directions.

Explanation :

• DNA is a double-stranded helix, with the two strands connected by hydrogen bonds. A bases are always paired with Ts, and Cs are always paired with Gs
• The two strands of DNA run in opposite directions to each other and are thus antiparallel
• The DNA double helix is anti-parallel, which means that the 5' end of one strand is paired with the 3' end of its complementary strand (and vice versa).
• Not only are the DNA base pairs connected via hydrogen bonding, but the outer edges of the nitrogen-containing bases are exposed and available for potential hydrogen bonding as well.