MadSci Network: Cell Biology

Re: Where does the nucleus go during prophase?

Date: Fri Oct 22 17:14:14 2004
Posted By: Christine Broussard, Assistant Professor of Biology
Area of science: Cell Biology
ID: 1095255438.Cb

The basic structure of the nucleus results from two contributing components, the
envelope and nuclear lamins.  The nuclear envelope originates from the
endoplasmic reticulum, 
and in most cells remains connected to it.  Nuclear lamins are proteins that
form a basket-like 
structure which gives the nucleus its shape.  The nuclear envelope surrounds the
nuclear lamins, 
such that the lamins and the inner nuclear membrane are in contact.  During the
cell cycle, 
proteins called cyclin dependent kinases alter the lamins so that they can no
longer make the 
basket structure.  When this happens the nuclear membrane disassembles and gets
resorbed into 
the endoplasmic reticulum, thus seeming to disappear.  When chromosomes begin to 
decondense in telophase, extensions of the endoplasmic reticulum associate with
and surround 
each chromosome.  These mini-nuclei, called karyomeres, fuse together to form
the new nucleus 
of the daughter cell.  Since anaphase led to the separation of the chromosomes
at opposite poles 
of the cell, two nuclei form.  During this process, lamins are returned to their
original state.  
They are imported into the newly forming nucleus, where they begin to assemble
the basket-like 
structure to support the nuclear membrane.

Lodish, Berk, Matsudaira, Kaiser, Krieger, Scott, Zipursky, and Darnell, 2003. 
Chapter 21: 
Regulating the Eukaryotic Cell Cycle.  Molecular Cell Biology, W.H. Freeman and

Thank you for your question!

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