Nuclear envelope is a derivative of rough endoplasmic reticulum. During cell division, nuclear membrane is disintegrated. The nuclear envelope transmembranc proteins are absorbed in the RER. Once the division is completed, RER reassembles the nuclear envelope.

Nuclear envelope is a double-membrane structure that surrounds the nucleus of eukaryotic cells. It separates the contents of the nucleus from the cytoplasm and plays a crucial role in regulating the movement of molecules into and out of the nucleus. The nuclear envelope is a derivative of the endoplasmic reticulum (ER), which is an extensive network of membranous tubules and sacs involved in various cellular processes.

The Origin of the Nuclear Envelope:
The nuclear envelope is derived from the ER during the process of nuclear division, known as mitosis or meiosis. As the nucleus prepares for division, the ER undergoes structural modifications to form the nuclear envelope. The following steps outline the formation of the nuclear envelope:

1. Dissolution of the Nuclear Envelope:
During early stages of mitosis or meiosis, the nuclear envelope disintegrates, allowing the genetic material to condense and become more accessible for segregation.

2. Fragmentation of the ER:
The ER, which is contiguous with the nuclear envelope, also undergoes fragmentation. This fragmentation occurs through the division of the tubules and sacs of the ER network.

3. Reformation of the Nuclear Envelope:
After the completion of nuclear division, the nuclear envelope is reassembled. The fragmented ER components reorganize around the segregated chromosomes to form a new nuclear envelope.

Structural Features of the Nuclear Envelope:
The nuclear envelope consists of two lipid bilayers, an inner nuclear membrane, and an outer nuclear membrane. These membranes are continuous with each other at numerous sites called nuclear pores. The nuclear pores are large protein complexes that regulate the passage of molecules, such as proteins and RNA, between the nucleus and the cytoplasm.

Key Functions of the Nuclear Envelope:
1. Nuclear Pore Complexes:
The nuclear envelope contains nuclear pore complexes that control the movement of molecules in and out of the nucleus. These complexes selectively transport molecules based on their size and specific signals.

2. Nuclear Localization and Export Signals:
The nuclear envelope plays a crucial role in regulating the localization of proteins and RNA molecules within the nucleus. It recognizes specific signals called nuclear localization signals (NLS) and nuclear export signals (NES) to facilitate the transport of molecules.

3. Protection of Genetic Material:
By separating the nucleus from the cytoplasm, the nuclear envelope provides a protective barrier for the genetic material within the nucleus. It prevents the entry of harmful substances and helps maintain the integrity of the genome.

In conclusion, the nuclear envelope is a derivative of the endoplasmic reticulum and is formed during nuclear division. It consists of two lipid bilayers and plays essential roles in regulating molecular transport, protecting the genetic material, and maintaining the organization of the nucleus.