<Ul> <Li> Vesicle fusion--where vesicles of nuclear membrane fuse together to rebuild the nuclear membrane </Li> <Li> Reshaping of the endoplasmic reticulum--where the parts of the endoplasmic reticulum containing the absorbed nuclear membrane envelop the nuclear space, reforming a closed membrane . </Li> </Ul> <Li> Vesicle fusion--where vesicles of nuclear membrane fuse together to rebuild the nuclear membrane </Li> <Li> Reshaping of the endoplasmic reticulum--where the parts of the endoplasmic reticulum containing the absorbed nuclear membrane envelop the nuclear space, reforming a closed membrane . </Li> <P> A study of the comparative genomics, evolution and origins of the nuclear membrane led to the proposal that the nucleus emerged in the primitive eukaryotic ancestor (the "prekaryote"), and was triggered by the archaeo - bacterial symbiosis . Several ideas have been proposed for the evolutionary origin of the nuclear membrane . These ideas include the invagination of the plasma membrane in a prokaryote ancestor, or the formation of a genuine new membrane system following the establishment of proto - mitochondria in the archael host . The adaptive function of the nuclear membrane may have been to serve as a barrier to protect the genome from reactive oxygen species (ROS) produced by the cells' pre-mitochondria . </P>

Describe the structure of the nucleus and nuclear envelope