The nucleolus is a region found within the cell nucleus that is concerned with producing and assembling the cell's ribosomes. Following assembly, ribosomes are transported to the cell cytoplasm where they serve as the sites for protein synthesis.
Within the cell nucleus there's a very specific part called the nucleolus. This does not contain the chromosomes. What this contains is the machinery necessary to assemble the cell's ribosomal RNAs. Ribosomal RNAs then are transported through the nuclear pores into the cytoplasm where they become part of the ribosome, which is the protein machinery. These ribosomal RNAs guide the messenger RNAs through the ribosomes and help in the protein translation, but they themselves are RNA's that do not become proteins. They're non-coding RNAs that help the messenger RNAs to undergo the protein translation process. These RNAs, like the other messenger RNAs, are made in the nucleus, but ribosomal RNAs are made in the nucleolus which is a very specific part of the cell nucleus.Julie A. Segre, Ph.D.