Nucleus is the brain of the cell and controls most of its functions. Thus without a nucleus, an animal cell or eukaryotic cell will die. The nucleus consists of all the genetic material in an animal cell and directs the functions of the cell, by regulating gene expression. It also maintains the integrity of genetic material. Without a nucleus, the cell will not know what to do and there would be no cell division. Protein synthesis would either cease or incorrect proteins would be formed. All this would result in cell death.
Unlike eukaryotes, prokaryotes have no nucleus and carry out all of their functions easily. Unfortunately, loss of a nucleus in animal cell will not convert it to prokaryotes and hence it will cease to function, after a while and die out.
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