The nuclear lamins are cytoskeletal fibres that coat the INE. They
provide attachment points for chromosomes during interphase, and
therefore help to organise the structure of the nucleus. During
prometaphase, they are phosphorylated, and allow the nucleus to
disintegrate. During telophase, lamin B-containing vesicles condense
around DNA to reform the nucleus.
The cell cycle consists of essentially four stages: an initial gap
phase, where the cell grows to a sufficient size to consider dividing,
followed by a phase of DNA synthesis. After the DNA has been
replicated, a second gap phase precedes the division, during which the
cell synthesises the other machinery required for chromosome
separation. Between each phase, there is a checkpoint, where the cell
'asks questions' of itself, to determine if e.g. all DNA has
been successfully replicated, whether the cell is sufficiently large to
divide, whether all chromosomes are aligned on the metaphase plate,
etc.