DNA Sequence Analysis: Bases, Bonds, and Structure

Steps:

• Sequence bases: A, G, C, A, A, T, G, C (8 nucleotides total).
• Pyrimidines (C, T): three present (positions 3:C, 6:T, 8:C). Statement 1 correct.
• Double-stranded complement: T, C, G, T, T, A, C, G; A-T pairs form 2 H-bonds, G-C form 3. Section has 2 H-bonds between A-T complementary bases. Statement 2 correct.
• Sugar-phosphate bonds: 8 nucleotides per strand yield 7 bonds per strand (phosphodiester linkages); double strand totals 14 bonds, not 20. Statement 3 incorrect.

Why B is correct:

• Selects statements 1 and 2, accurate per pyrimidine definition (single-ring bases C/T) and Watson-Crick base pairing (A-T: 2 H-bonds).

Why the others are wrong:

• A: Includes false statement 3 (bond count uses formula 2 × (n-1) for n=8 nucleotides).
• C: Excludes true statement 2 on H-bonding.
• D: Includes false statement 3, excludes true statement 1.

Final answer: B