In the structure of DNA, which nitrogenous base pairs with cytosine?

• A. Thymine
• B. Adenine
• C. Guanine
• D. Uracil

Answer: (C)

Verified step by step guidance

1. Recall that DNA is composed of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
2. Understand that base pairing in DNA follows Chargaff's rules, where adenine pairs with thymine, and cytosine pairs with guanine.
3. Recognize that cytosine is a pyrimidine base and pairs specifically with guanine, a purine base, through three hydrogen bonds.
4. Note that uracil is not found in DNA; it replaces thymine in RNA, so it does not pair with cytosine in DNA.
5. Therefore, the nitrogenous base that pairs with cytosine in DNA is guanine.