Abstract

The synthesis of deoxyribonucleic acid (DNA) takes place in the cell cycle sometime before cell division and the replicated DNA is transferred to the “daughter” nuclei during mitosis. If tritiated thymidine, a specific precursor of DNA, is present during the period of DNA production, radioactive DNA is synthesized and the daughter nuclei also become radioactive. By autoradiography, the epidermal cells of mice and rats have been observed to be labeled at lj (1), 3 and 8 hours (2, 3) after injection of thymi-dine-H3sp>. The labeled cells were seen in the deeper part of the epidermis where mitoses are usually seen and DNA duplication must occur. Six months later, however, none of the labeled cells were present in the epidermis (2). Since DNA is considered to be metabolically inert under ordinary conditions, loss of tritium must have occurred either by (a) dilution of the label resulting from many cell divisions, so that the level of radioactivity was too low for identification; or (b) disappearance by the same process as causes the loss of the nucleus at the surface of the epidermis. Cells formed in the deeper part of the epidermis slowly move out towards the surface and are lost by desquamation, although the precise role played by each cell in this action is not yet known.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.