The cell nucleus controls most cell processes and contains DNA. The nuclear envelope surrounds the nucleus and contains pores, which regulate what goes in and out of this control center.
The cell nucleus contains the chromatin, nucleolus, RNA and proteins suspended in a jelly-like matrix. The nuclear envelope encloses all these structures. Two membranes make up the nuclear envelope. The pores in the nuclear envelope restrict passage of bigger molecules such as DNA and proteins, but water, ions and smaller molecules pass through freely.
The nucleolus is a spherical structure that lies toward the center of the nucleus. Ribosomal RNA, DNA and proteins live inside this structure. Some ribosomes and partial ribosomes also inhabit the nucleolus, which is where ribosomes are made. When the ribosomes are complete, they move from the nucleus to the cytoplasm where they become the sites of protein synthesis.
The chromatin are structures that house the DNA, the molecule that provides the code for the making of proteins. During cell division, the chromatin condense into structures called chromosomes. When the cell needs to make certain proteins, the DNA is used as a template for the making of RNA. This molecule is the messenger RNA. Because DNA cannot pass through the nuclear envelope to the rest of the cells, the messenger RNA serves this function. This molecule travels to the ribosomes in the cytoplasm to be used as the template for the making of proteins.