The nucleus is a cellular organelle that is only present in eukaryotes. Prokaryotes and archaea do not have DNA contained in a nucleus. The nucleus is usually the largest organelle present in a cell. Its main function is to regulate gene expression; it also controls cellular growth and replication.Continue Reading
The DNA contained in a nucleus is tightly packed into chromosomes, which must be unwound prior to cell division and DNA replication. DNA transcription into mRNA takes place in the nucleus. Translation of the mRNA into peptides is done by ribosomes in the cytoplasm.
The nucleus is protected by a structure called the nuclear envelope. The nuclear envelope is impermeable to larger molecules, but nuclear pores in the envelope allow the passage of small molecules, like mRNA, into the nucleus. The main role of the nuclear envelope is to separate the nucleus from the cytoplasm.
Not every eukaryotic cell has a nucleus. In many multicellular organisms, such as humans, the nucleus is removed naturally and is normal for the function of a particular cell. Two examples of this are human red blood cells and platelets. Since these cells do not contain a nucleus, they are unable to replicate. Other cells may contain multiple nuclei. This phenomenon is seen in some protozoa and fungi.Learn more about Cells