In 1953, Watson and Crick published a paper: A Structure for Deoxyribose Nucleic Acid. Based on available data from X-ray diffraction patterns and 3D conceptualization through model building, Watson and Crick proposed that DNA is a double helix - a twisted ladder - with two phosphate-based backbones and "runged" nucleotides that pair. Their paper ended with this comment:
It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.
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