Re: DOES THE NUCLEUS HAVE ANY INTERNAL STRUCTURES?

The nucleus has lots of internal structure, although much of it isn't 
visible, even under a microscope. The major piece that is visible is the 
nucleolus, often seen as a darkly-staining part of the nucleus that is 
quite large. Within the past few decades, we've learned a lot about the 
structure of the nuclear envelope, and specifically the lamin proteins 
that form a sort of mesh on the inner surface of that membrane.

There is increasing evidence that many of the processes that go on in the 
nucleus, such as replication, transcription, and mRNA processing, take 
place in specific locations. For replication, for instance, rather than 
DNA polymerase (and all of the other proteins involved) running around 
finding origins to start replication, it appears that "replication 
machinery" is stationary, and the DNA comes to it.

No doubt as increasingly sensitive techniques are used to visualize 
processes within the nucleus we will continue to discover specialized 
locations involved in even more processes.