CLAUDIA STOCKER / SCIENCE PHOTO LIBRARY CLAUDIA STOCKER / SCIENCE PHOTO LIBRARY
Adenine-thymine bond. Illustration showing the hydrogen bonding between the nucleotides cytosine (left) and guanine (right). Thymine and adenine are two of the four nitrogenous bases found in DNA (deoxyribonucleic acid). Adenine and thymine always pair together. Hydrogen bonds are weak bonds that form when a hydrogen atom is bound to a highly electronegative element such as nitrogen, chlorine or oxygen. They only occur over short distances and are easily formed and broken.
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