Which base always pairs with thymine in DNA?

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

Answer: (B)

In DNA, thymine is one of the four nucleotide bases, and it pairs specifically with adenine. This pairing occurs through the formation of hydrogen bonds: thymine forms two hydrogen bonds with adenine, ensuring the stability of the DNA double helix structure. This base pairing is a fundamental aspect of DNA replication and transcription, as it allows for accurate copying of genetic information.

Cytosine and guanine pair together, while uracil is found in RNA and not in DNA. Therefore, urinary pairing does not apply to DNA as thymine is exclusive in its pairing with adenine. Recognizing these specific pairs is crucial in understanding the mechanics of molecular biology, especially in processes like genetic encoding and the synthesis of RNA from DNA templates.