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The double membrane of the nucleus enclosing DNA and any other genetic material in a   eukaryotic cell is called the nuclear membrane. It separates the DNA from the cytosol. The space between the twomembranes is called the perinuclear space and is from 20 to 100 nm wide. The rough endoplasmic reticulum connects with the outer membrane. You can easily see these structures in a raw chicken egg. The nuclear membrane is often referred to as the nuclear envelope.

Pores on the nuclear membrane regulate the exchange of materials likeproteins between the nucleus and the cytoplasm. Inside the inner membrane, nuclear lamina form a network of filaments that play an important role in mitosis and in meiosis.

During prophase in mitotic cell division, the nuclear membrane disintegrates after the chromotids start to replicate and formchromosomes. By the end of metaphase, the nuclear membrane is completely gone, releasing the nuclear lamina, which form spindle fibers that pull apart the chromosomes from the chromotins, and help to repel them to different ends of the cell. 

In certain eukaryotes like yeast, a closed mitosis is undergone, in which chromosomes remain within the nuclear membrane; the membrane itself undergoes a division as the two daughter cells divide.



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Comparison of a typical eukaryotic cell with a typical prokaryotic cell (bacterium). The drawing on the left highlights the internal structures of eukaryotic cells, including the nucleus (light blue), the nucleolus (intermediate blue), mitochondria (orange), and ribosomes (dark blue). The drawing on the right demonstrates how bacterial DNA is housed in a structure called the nucleoid (very light blue), as well as other structures normally found in a prokaryotic cell, including the cell membrane (black), the cell wall (intermediate blue), the capsule (orange), ribosomes (dark blue), and a flagellum (also black). |


What Prokaryotic and Eukaryotic Cells Have in Common

Both have DNA as their... [continues]

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