when does the nuclear membrane disappear?

The nuclear membrane (nuclear envelope) disappears during late prophase / prometaphase of mitosis in eukaryotic cells.

Key moment in the cell cycle

• During prophase , chromosomes condense and the mitotic spindle begins to form while the nuclear membrane is still mostly intact.

• As the cell progresses into late prophase / prometaphase , the nuclear envelope breaks down, allowing spindle microtubules to attach to chromosomes.

• Later, in telophase , a new nuclear membrane re-forms around each set of separated chromosomes.

What “disappears” actually means

• The membrane does not vanish instantly; its proteins and lipids are disassembled and redistributed into the endoplasmic reticulum and cytoplasm.

• This breakdown is driven by phosphorylation of nuclear envelope proteins (including nuclear pore complexes and nuclear lamins) by mitotic kinases such as CDK1.

Simple exam-style answer

• For school and entrance-exam questions, the accepted answer is:
  • “The nuclear membrane disappears during late prophase of mitosis (often called prometaphase).”

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