Which statement about the structure of the DNA double helix is correct?

Which statement about the structure of the DNA double helix is correct?

• A. Nitrogenous bases pair with purine or pyrimidine bases
• B. The two DNA strands are oriented in the same direction
• C. The amount of guanine equals cytosine in a DNA sequence
• D. The sugar-phosphate backbone faces the interior

Answer: (C)

The correct understanding of the DNA double helix revolves around the complementary nature of the nitrogenous bases, the orientation of the strands, and the structure of the backbone. The statement that the amount of guanine equals cytosine in a DNA sequence is accurate due to Chargaff's rules, which state that in a double-stranded DNA molecule, the amount of guanine (G) always equals the amount of cytosine (C). This pairing is essential for the integrity and stability of the genetic information, as G pairs with C through three hydrogen bonds. In contrast, while purine and pyrimidine pairing does occur (adenine pairs with thymine, and guanine pairs with cytosine), the phrasing regarding pairing without specificity does not capture the essence of base pairing in the double helix accurately. Additionally, the orientation of the two strands is antiparallel, meaning one strand runs in the 5' to 3' direction while the other runs 3' to 5', rather than being in the same direction. Lastly, the sugar-phosphate backbone of DNA forms the exterior of the helix, while the nitrogenous bases are oriented inward to pair with each other, which further emphasizes that the correct structure is key

The correct understanding of the DNA double helix revolves around the complementary nature of the nitrogenous bases, the orientation of the strands, and the structure of the backbone. The statement that the amount of guanine equals cytosine in a DNA sequence is accurate due to Chargaff's rules, which state that in a double-stranded DNA molecule, the amount of guanine (G) always equals the amount of cytosine (C). This pairing is essential for the integrity and stability of the genetic information, as G pairs with C through three hydrogen bonds.

In contrast, while purine and pyrimidine pairing does occur (adenine pairs with thymine, and guanine pairs with cytosine), the phrasing regarding pairing without specificity does not capture the essence of base pairing in the double helix accurately. Additionally, the orientation of the two strands is antiparallel, meaning one strand runs in the 5' to 3' direction while the other runs 3' to 5', rather than being in the same direction. Lastly, the sugar-phosphate backbone of DNA forms the exterior of the helix, while the nitrogenous bases are oriented inward to pair with each other, which further emphasizes that the correct structure is key