How many hydrogen bonds connect adenine and thymine?

How many hydrogen bonds connect adenine and thymine?

• A. 1
• B. 3
• C. 4
• D. 2

Answer: (D)

In DNA, base pairing is guided by hydrogen bonds between complementary bases. Adenine pairs with thymine using two hydrogen bonds. One bond forms between adenine’s N6 amino group (which donates a hydrogen) and thymine’s O4 carbonyl; the other forms between adenine’s N1 nitrogen (which accepts a hydrogen) and thymine’s N3–H. This two-bond connection helps stabilize the A–T pair and contributes to the DNA double helix structure. By contrast, guanine pairs with cytosine through three hydrogen bonds, so A–T connections involve two bonds.

In DNA, base pairing is guided by hydrogen bonds between complementary bases. Adenine pairs with thymine using two hydrogen bonds. One bond forms between adenine’s N6 amino group (which donates a hydrogen) and thymine’s O4 carbonyl; the other forms between adenine’s N1 nitrogen (which accepts a hydrogen) and thymine’s N3–H. This two-bond connection helps stabilize the A–T pair and contributes to the DNA double helix structure. By contrast, guanine pairs with cytosine through three hydrogen bonds, so A–T connections involve two bonds.