If radioactively labeled uracil is added to a culture of mammalian cells, which cell structure will incorporate it?

Incorporation of radioactively labeled uracil in mammalian cells primarily occurs in the nucleus. Uracil is a nucleotide base that is essential for the synthesis of RNA. When uracil is introduced into the culture, cells take it up and use it to synthesize RNA, particularly in the nucleus, where transcription takes place.

During transcription, DNA is transcribed into messenger RNA (mRNA), and uracil replaces thymine in RNA. Therefore, newly synthesized RNA molecules in the nucleus will incorporate the labeled uracil, which can then be detected using radioactive tracing techniques.

While ribosomes play a crucial role in protein synthesis and are involved in the translation of mRNA into proteins, they do not directly incorporate uracil or synthesize RNA. Instead, they facilitate the translation of existing mRNA into polypeptide chains.

The other cellular structures mentioned, such as mitochondria and the endoplasmic reticulum, do not play a direct role in the incorporation of uracil. Mitochondria are primarily involved in energy production, while the endoplasmic reticulum is key in synthesizing proteins and lipids but not in RNA synthesis. Thus, the nucleus is the primary site for the incorporation of urac