Which statement describes complementary base pairing in DNA?

Which statement describes complementary base pairing in DNA?

• A. Each base can only bond with another copy of itself in DNA.
• B. Each base type can only pair with another specific base in DNA.
• C. The bases can only exist as double strands in nucleic acids.
• D. Bases form pairs in nonspecific combinations in DNA.

Answer: (B)

Complementary base pairing means each DNA base has a single specific partner, so two strands can line up with a uniform width. In DNA, adenine pairs with thymine and cytosine pairs with guanine, connected by hydrogen bonds. This specific pairing means the sequence on one strand dictates the sequence on the opposite strand, enabling accurate replication and transmission of genetic information. Think of why this is the best description: it captures the idea that bases do not pair with themselves and that pairing is not random. The notion of self-pairing would misrepresent A with A or C with C, which doesn’t happen. The idea that bases exist only as double-stranded structures ignores that nucleic acids can be single-stranded and that DNA is often unwound during processes like replication. And the idea of nonspecific pairing contradicts the observed, highly regular A–T and C–G rules that underlie the stability and fidelity of the DNA double helix.

Complementary base pairing means each DNA base has a single specific partner, so two strands can line up with a uniform width. In DNA, adenine pairs with thymine and cytosine pairs with guanine, connected by hydrogen bonds. This specific pairing means the sequence on one strand dictates the sequence on the opposite strand, enabling accurate replication and transmission of genetic information.

Think of why this is the best description: it captures the idea that bases do not pair with themselves and that pairing is not random. The notion of self-pairing would misrepresent A with A or C with C, which doesn’t happen. The idea that bases exist only as double-stranded structures ignores that nucleic acids can be single-stranded and that DNA is often unwound during processes like replication. And the idea of nonspecific pairing contradicts the observed, highly regular A–T and C–G rules that underlie the stability and fidelity of the DNA double helix.