 Because the nuclear membrane is impermeable to large molecules , nuclear pores are required that regulate nuclear transport of molecules across the envelope . The pores cross both nuclear membranes , providing a channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions . Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes . Although the interior of the nucleus does not contain any membrane @-@ bound sub compartments , its contents are not uniform , and a number of sub @-@ nuclear bodies exist , made up of unique proteins , RNA molecules , and particular parts of the chromosomes . The best @-@ known of these is the nucleolus , which is mainly involved in the assembly of ribosomes . After being produced in the nucleolus , ribosomes are exported to the cytoplasm where they translate mRNA . 
 Because the nuclear membrane <a href='drop_aux' title='1'><mark>is</mark></a>impermeable to large molecules , nuclear pores are required that regulate nuclear transport of molecules across the envelope . The pores cross both nuclear membranes , providing a channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions . Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes . Although the interior of the nucleus <a href='uninflect' title='2'><mark>does</mark></a> not contain <a href='None' title='3'><mark>any</mark></a>membrane <a href='negative_concord' title='4'><mark>@-@</mark></a> bound sub compartments , its contents <a href='negative_concord' title='5'><mark>are</mark></a> <a href='negative_concord' title='6'><mark>not</mark></a>uniform , and a number of sub @-@ nuclear bodies exist , made up of unique proteins , RNA molecules , and particular parts of the chromosomes . The best @-@ known of these <a href='drop_aux' title='7'><mark>is</mark></a>the nucleolus , which is mainly involved in the assembly of ribosomes . After being produced in the nucleolus , ribosomes are exported to the cytoplasm where they translate mRNA . 
Bc the nuclear membrane impermeable to bigass molecules , nuclear pores r required dat regulate nuclear transport of molecules across da envelope . Tdapores cross both nuclear membranes , providing a channel thru which larger molecules must b actively transported by carrier proteins while allowing free movement of small molecules and ions . Movement of large molecules such as proteins and RNA through thdaores is required for both gene expression and the maintenance of chromosomes . Although the interior of the nucleus do not contain membrane no @-@ bound sub compartments , its contents ain't uniform , and a number of sub @-@ nuclear bodies exist , made up of unique proteins , RNA molecules , and particular parts of the chromosomes . The best @-@ known of these thedacleolus , which is mainly involved in the daembly of ribosomes . After bein produced in the ndaeolus , ribosomes are exported to the cytoplasm where they translate mRNA .