Advanced Placement (AP) Biology Practice Exam

Which of the following best describes DNA?

1. Nucleic acid

2. Single helix

3. Controls protein synthesis

4. Double helix

The correct answer is: Double helix

DNA, or deoxyribonucleic acid, is best described as a double helix. This structure consists of two long strands of nucleotides wound around each other, forming a spiral shape. The two strands are held together by complementary base pairing between adenine and thymine, and cytosine and guanine. The double helix arrangement is crucial for the stability of the DNA molecule and plays a significant role in the processes of replication and transcription. While DNA can be categorized as a nucleic acid and is involved in controlling protein synthesis, these descriptions do not capture the unique structural characteristic that is fundamental to its function and stability. The single helix structure does not accurately represent DNA, as it is specifically the double helix form that is essential for its biological roles.