Nucleus

The nucleus is the largest organelle of most eukaryotic cells and contains proteins and genetic material (DNA and some RNA). Nuclear proteins include histones that control the structural state of DNA and transcription factors that regulate gene expression. It is important to remember that nucleoproteins are synthesized in the cytoplasm and then transported into the nucleus. The nuclear envelope surrounds the nucleus and comprises two concentric membranes bilayers that are penetrated by nuclear pore complexes. The pores allow for the transport of proteins into and out of nucleus. Also evident is the nucleolus where ribosome synthesis occurs and heterochromatin that contains transcriptionally inactive DNA.