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Figure 2–43. A scheme illustrating the semi-conservative manner of DNA- replication. Each of the two chains serves as a matrix for the formation of a new complementary chain (After Meselson and Stahl, 1958). I — initial (parental) molecule; II — first generation (“daughter” molecules); III — second generation (molecules — “grandsons”)
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Figure 2–44. Schematic presentation of the DNA-replication. The parental chains separate at the replication fork. Each parental chain serves as a template for the synthesis of a new chain.
The packing of DNA with proteins is a key problem. That is why it provokes general
interest. In their monograph “The Eukaryotic Chromosome” Bostock and
Sumner (1981) pay attention to two unsolved questions related to the linear
organization of the nucleosome structures: Whether DNA is found outside the histone
complexes or is it situated inside them? Is the entire DNA in the nucleus packed in one
and the same fashion or are there separate portions in the chromatin (transcribing or
replicating chromatin) that are packed in another way? Of a great interest is the
publication of Tsanev and Russev (1974) on the distribution of the newly-synthesized
histones at the time of DNA replication. The authors have proved experimentally that during the
replication the existing histones remain bound to the parental DNA-chain,
while the newly-synthesized histones bind to the new DNA-chain.
The results obtained by them confirm the ones of Hanckok (1969, 1970)
postulating that histones are conservative elements of chromatin distributing