Which of the following correctly identifies the components of a section of double-stranded DNA?

• A. Phosphate groups are paired with nitrogenous bases in the center, while sugars are on the outside.
• B. The sugar-phosphate backbone is on the outside, and the nitrogenous bases are on the inside, paired by hydrogen bonds.
• C. The nitrogenous bases form the backbone, and the sugar-phosphate groups are paired in the center.
• D. The sugar and base are both on the outside, with phosphates forming the inner core.

Answer: (B)

Verified step by step guidance

1. Understand the structure of DNA: DNA is a double-stranded molecule composed of nucleotides. Each nucleotide consists of three components: a phosphate group, a sugar molecule (deoxyribose), and a nitrogenous base.
2. Visualize the arrangement of DNA: The sugar-phosphate backbone forms the outer structure of the DNA double helix, providing stability and support. The nitrogenous bases are located on the inside of the helix, paired together by hydrogen bonds.
3. Recall the pairing of nitrogenous bases: Adenine (A) pairs with Thymine (T) via two hydrogen bonds, and Cytosine (C) pairs with Guanine (G) via three hydrogen bonds. These base pairs are responsible for the genetic coding within DNA.
4. Clarify the incorrect statements: Phosphate groups are not paired with nitrogenous bases in the center; instead, they are part of the sugar-phosphate backbone on the outside. Similarly, nitrogenous bases do not form the backbone; they are paired in the center of the helix.
5. Identify the correct statement: The sugar-phosphate backbone is on the outside, and the nitrogenous bases are on the inside, paired by hydrogen bonds. This arrangement is crucial for the structural integrity and function of DNA.