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Question
Which property of DNA double helix led Watson and Crick to hypothesise semi-conservative mode of DNA replication? Explain.
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Solution
Watson and Crick proposed a semi-conservative mode of DNA replication based on the molecule's antiparallel, double-stranded structure. They suggested that the two strands of the DNA molecule uncoil and separate, with each strand serving as a template for the production of a new (complementary) strand alongside it. The template and its complement then combine to generate a new double strand of DNA that is identical to the original molecule. The sequence of bases that should be present in the new strands is easily predicted because they will be complementary to the bases present in the old strands. A will partner with T, T with A, C with G, and G with C. As a result, two daughter DNA molecules are created that are identical to the parent molecule; each daughter DNA molecule is made up of one new and one old strand. This replication mechanism is referred to as semi-conservation since each daughter molecule only contains one conserved parent strand. Later, experiments by Joseph Taylor, Meselson and Stahl verified it.
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| Number of nucleotide bases | ||||
| Adenine | Cytosine | Guanine | Thymine | |
| Strand 1 | 4 | 4 | ||
| Strand 2 | 5 | |||
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