 A more recent proposal , the exomembrane hypothesis , suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane ; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits . 
 A more recent proposal , the exomembrane hypothesis , <a href='uninflect' title='1'><mark>suggests</mark></a> that the nucleus instead originated from a single ancestral cell <a href='null_relcl' title='2'><mark>that</mark></a>evolved a second exterior cell membrane ; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits . 
A more recent proposal , da exomembrane hypothesis , suggest that the nucleus instead originated from a single ancestral cell evolved a second exterior cell membrane ; the interior membrane enclosing tdaoriginal cell then became the nuclear membrane and evolved increasingly elaborate pore structures fir passage of internally synthesized cellular components such as ribosomal subunits .