At the center of the cell is the nucleolus. The nucleolus holds the RNA and the ribosomes in their own various stages of synthesis. The nucleolus surrounds the cell. This special part of the nucleus allows for certain proteins and materials to enter the nucleus like water or ATP.
Nucleolus
http://hyperphysics.phy-astr.gsu.edu/hbase/biology/celnuc.html
Nuclear Envelope
http://www.biology-online.org/dictionary/Nuclear_envelope
Nucleolus
http://hyperphysics.phy-astr.gsu.edu/hbase/biology/celnuc.html
Nuclear Envelope
http://www.biology-online.org/dictionary/Nuclear_envelope