mjs419 at psu.edu
Mon Mar 15 21:28:39 EST 1999
ebbes wrote in message <7cfnp9$26iu$1 at news-inn.inet.tele.dk>...
>Can somebody tell me why nucleolus disapears in the first part of the cell
>division. (in prophasis)
The nucleolus is not excluded from the rest of the nucleus by a
membrane- it is a region of highly transcribed chromosomal DNA, its rRNA
transcripts and the protein the rRNA binds to. It only appears when the
genes for rRNA transcription are active. During mitosis, transcription
there is halted as the chromosomes condense. The rRNA and proteins leave
the cell and the chromosomes undergo mitosis. After the two daughter cells
reform, transcription picks up again, and tiny nucleoli reform and
eventually fuse into the nucleolus as rRNA synthesis again occurs.
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