Which of the following statements correctly describes the structure of DNA?
A) It consists of a single chain of nucleotides
B) It is made up of three nucleotide strands
C) It has no hydrogen bonds between the bases
D) It contains only two nitrogenous bases
E) It has a double-stranded helical structure
IMAT 2026 · Question 30
Q30 - Structure of DNA and RNA
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The correct answer is E) It has a double-stranded helical structure.
DNA is made of two antiparallel strands wound into a double helix. The strands are held together by hydrogen bonds between complementary bases: A–T (2 hydrogen bonds) and G–C (3 hydrogen bonds).
A) Incorrect: A single strand describes most RNA, not DNA.
B) Incorrect: DNA has two strands. A three-stranded model was proposed (by Pauling) and turned out to be wrong.
C) Incorrect: Hydrogen bonds between the bases are what hold the two strands together.
D) Incorrect: DNA has four bases: adenine, thymine, guanine and cytosine.
E) Correct: DNA is a double-stranded helix.
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