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The Structure of Cells

Author(s): Center for Educational Outreach

The Nucleus

The nuclear envelope contains proteins, and the nuclear pores are important in regulating the entry and exit of protein and RNAs. 

When the cell is in growth and maintenance phases, proteins are attached to its chromosomes, resulting in a thread-like appearance (see illustration above). When a cell is ready to divide, its chromatin condenses into different chromosomes. 

The nucleolus—prominent in a nucleus that is not dividing—is the site of ribosomal RNA production.