Which two bases are present in equal amounts in a double-stranded DNA molecule?

• A. Adenine and Thymine
• B. Cytosine and Adenine
• C. Guanine and Thymine
• D. Adenine and Guanine

Answer: (A)

Verified step by step guidance

1. Recall Chargaff's rules, which state that in double-stranded DNA, the amount of adenine (A) equals the amount of thymine (T), and the amount of cytosine (C) equals the amount of guanine (G).
2. Understand that this equality arises because adenine pairs specifically with thymine via two hydrogen bonds, and cytosine pairs with guanine via three hydrogen bonds, maintaining base pairing complementarity.
3. Express this relationship mathematically as \(\text{[A]} = \text{[T]}\) and \(\text{[C]} = \text{[G]}\), where \(\text{[X]}\) denotes the concentration or amount of base X.
4. Use this knowledge to analyze the options given and identify which pair of bases are present in equal amounts in double-stranded DNA.
5. Conclude that the correct pair is adenine and thymine, as they are complementary bases present in equal amounts according to Chargaff's rules.