. Cytology. Cytology. somes at the subsequent metaphase will contain a labeled chromatid (Hughes, 1958). Studies using tritiated thymidine as a means of follow- ing DNA metabolism during chromosome replication indicate that this label is built into the DNA of the chromosome as a part of a physical entity that remains intact during succeeding replications (Hughes, 1958). The interphase chromosome before replication would be com- posed of two such entities which are probably complementary to each other. After replication of each entity to give a chromosome with four entities, the whole chromosom
. Cytology. Cytology. somes at the subsequent metaphase will contain a labeled chromatid (Hughes, 1958). Studies using tritiated thymidine as a means of follow- ing DNA metabolism during chromosome replication indicate that this label is built into the DNA of the chromosome as a part of a physical entity that remains intact during succeeding replications (Hughes, 1958). The interphase chromosome before replication would be com- posed of two such entities which are probably complementary to each other. After replication of each entity to give a chromosome with four entities, the whole chromosome then divides so that by metaphase, each chromatid or daughter chromosome regularly receives an "original" and a "new" entity. Whether or not the two physical entities of the interphase. Figure 4-25. Diagrammatic Representation of the Structural Organiza- tion and Mode of Replication of the Chromosome as Revealed by Labeling with Tritiated Thymidine. The nonlabeled DNA subunits are shown as solid lines, while the labeled subunits appear as dashed lines. The dots rep- resent grains as seen in the autoradiographs. (From Taylor, J. H., Woods, P. S., and Hughes, W. L., 1957. "The Organization and Duplication of Chro- mosomes as Revealed by Autoradiographic Studies Using Tritium-labeled Thymidine," Proc. Natl. Acad. 43, Fig. 3, p. 125.) chromosome associated with the uptake of tritiated thymidine represent the chromonemata is not known. While the evidence is fairly good that the major role of DNA is ge- netic, studies of protein synthesis in isolated nuclei have suggested another possible function, namely, as a cofactor in the nuclear aerobic synthesis of ATP. Allfrey and Mirsky (1959) have shown that when a large fraction of the DNA is removed from isolated nuclei there is a loss of capacity for ATP synthesis, amino acid incorporation, and for RNA synthesis. This loss can be reversed by addition of DNA from almost any source, RNA, polyadenylic a
Size: 2875px × 869px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
