Summary. Base pairs<span> occur when </span>nitrogenous bases<span>make hydrogen bonds with each other. Each </span>base<span> has a specific partner: guanine with </span>cytosine<span>, </span>adenine<span> with thymine (in </span>DNA<span>) or </span>adenine<span> with uracil (in RNA). The hydrogen bonds are weak, allowing </span>DNA<span> to 'unzip'.</span>
The nitrogenous bases form base pair following the complementary rule suggested by the Chargaff.
The Chargaff suggested that purine binds pyrimidine where adenine will bind thymine and guanine will bind the cytosine respectively in a DNA.
This adenine binds the guanine by forming two hydrogen bonds between them whereas the cytosine binds guanine by three hydrogen bonds.
