Which statement about the DNA double helix is true? Choose 1 answer: A It allows for fully conservative replication. B The double helix is made up of a single, continuous strand of DNA. C Adenine and cytosine pair together, and guanine and thymine pair together. D The two strands are antiparallel.
The Correct Answer and Explanation is:
Correct Answer: D. The two strands are antiparallel.
Explanation:
DNA (Deoxyribonucleic Acid) is the molecule that carries genetic information in all living organisms. The structure of DNA is famously known as the double helix, first described by James Watson and Francis Crick in 1953. This structure is composed of two strands that wind around each other like a twisted ladder.
The correct description of the structure is that the two strands of DNA run in opposite directions—this is known as being antiparallel. One strand runs in the 5′ to 3′ direction, while the complementary strand runs 3′ to 5′. This orientation is crucial for processes such as DNA replication and transcription, as enzymes like DNA polymerase can only work in the 5′ to 3′ direction.
Let’s consider why the other answer choices are incorrect:
- A. It allows for fully conservative replication: This is incorrect. DNA replicates through a semi-conservative mechanism, where each new double helix contains one original (parental) strand and one newly synthesized strand.
- B. The double helix is made up of a single, continuous strand of DNA: False. The DNA double helix consists of two complementary strands of DNA, not a single continuous strand.
- C. Adenine and cytosine pair together, and guanine and thymine pair together: This is incorrect. In DNA, the base pairing rules are Adenine (A) pairs with Thymine (T) and Guanine (G) pairs with Cytosine (C). These pairings are due to specific hydrogen bonding patterns: A-T pairs have two hydrogen bonds, while G-C pairs have three, making them more stable.
In conclusion, the antiparallel nature of the DNA double helix is a defining feature that enables accurate replication and gene expression, making Option D the correct answer.
