In DNA, which base always pairs with $\mathrm{adenine}$?

• A. $\mathrm{Thymine}$
• B. $\mathrm{Uracil}$
• C. $\mathrm{Cytosine}$
• D. $\mathrm{Guanine}$

Answer: (A)

Verified step by step guidance

1. Understand the structure of DNA: DNA is composed of two strands forming a double helix, with each strand consisting of a sequence of nucleotides.
2. Identify the four nucleotide bases in DNA: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
3. Recall the base pairing rules in DNA: Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G).
4. Apply the base pairing rule to the problem: Since the question asks which base pairs with adenine, use the rule that adenine pairs with thymine.
5. Note that uracil is not found in DNA: Uracil (U) is found in RNA, where it pairs with adenine instead of thymine.