The nucleolus is where ribosomes are assembled. An organism's DNA is arranged into one or more chromosomes. All the DNA present in a particular cell represents the organisms genome . Bacteria have a single chromosome One end of the DNA is attached to the other end forming a circular chromosome. The E. coli chromosome contains 4 million base pairs.
Plasmids are also circular.
Plasmids often contain genes for antibiotic resistance. Transposons are pieces of DNA that can move around in the genome, and are typically found on plasmids. Antibiotic resistance genes are found within transposons. In Eukaryotes, the genome is often spread out among many chromosomes. In multicellular eukaryotes, two copies of the genome are often present.