Sagot :
Purines form hydrogen bonds to pyrimidines. Adenine pairs up with Thymine (in DNA) and Uracil (in RNA) and Guanine pairs with Cytosine. A-T pairing has 2 hydrogen bonds and C-G pairing has 3 hydrogen bonds.
in DNA,
ADENINE -(always pair with)- THYMINE
CYTOSINE -(always pair with)- GUANINE
ADENINE -(always pair with)- THYMINE
CYTOSINE -(always pair with)- GUANINE