What is the base pairing rule in DNA?

What is the base pairing rule in DNA?

• A. A pairs with G, T with C
• B. A pairs with T, G with C
• C. A pairs with C, G with T
• D. A pairs with T, C with G

Answer: (B)

DNA base pairing follows a precise rule: adenine pairs with thymine, and guanine pairs with cytosine. This pairing pattern, A with T and G with C, is driven by hydrogen bonding—A and T form two hydrogen bonds, while G and C form three. Those bonds help stabilize the double helix and keep the overall width uniform, which is important for accurate replication and structure. Because each strand serves as a template, the sequence on one strand determines the sequence on the other, a relationship reflected by Chargaff’s observation that A equals T and G equals C in natural DNA. Pairs like A with G or A with C would mix two different types of bases in a way that disrupts the geometry and stability of the double helix, so they don’t occur in standard DNA pairing.

DNA base pairing follows a precise rule: adenine pairs with thymine, and guanine pairs with cytosine. This pairing pattern, A with T and G with C, is driven by hydrogen bonding—A and T form two hydrogen bonds, while G and C form three. Those bonds help stabilize the double helix and keep the overall width uniform, which is important for accurate replication and structure. Because each strand serves as a template, the sequence on one strand determines the sequence on the other, a relationship reflected by Chargaff’s observation that A equals T and G equals C in natural DNA. Pairs like A with G or A with C would mix two different types of bases in a way that disrupts the geometry and stability of the double helix, so they don’t occur in standard DNA pairing.