Which statement about base pairing is correct?

Which statement about base pairing is correct?

• A. Adenine always bonds with thymine, never with cytosine.
• B. Adenine bonds with cytosine as often as thymine.
• C. Thymine bonds with cytosine.
• D. Adenine bonds with guanine.

Answer: (A)

In DNA, bases pair specifically through hydrogen bonding and shape complementarity. Adenine forms two hydrogen bonds with thymine, creating the A–T pair, while cytosine pairs with guanine with three hydrogen bonds. This precise pairing is what maintains the double-helix structure and supports accurate replication. Therefore, the statement that adenine bonds with thymine (and not with cytosine) captures the canonical pairing pattern in DNA. Adenine does not pair with cytosine, and thymine does not pair with cytosine under normal conditions, while adenine does not pair with guanine.

In DNA, bases pair specifically through hydrogen bonding and shape complementarity. Adenine forms two hydrogen bonds with thymine, creating the A–T pair, while cytosine pairs with guanine with three hydrogen bonds. This precise pairing is what maintains the double-helix structure and supports accurate replication. Therefore, the statement that adenine bonds with thymine (and not with cytosine) captures the canonical pairing pattern in DNA. Adenine does not pair with cytosine, and thymine does not pair with cytosine under normal conditions, while adenine does not pair with guanine.