Plasmids

Many bacteria contain small, circular, double-stranded DNA molecules apart from chromosome. Several copies of a single plasmid may be present in the cell. Many plasmids contain carry genes that coding for the production of enzymes. Such as antibiotic which protect the cell from toxic substances.

 Nucleoid

 A nucleoid is the part of a prokaryote, or single-celled organism. Prokaryotes do not contain nuclei. Therefore, the genetic material for the organism exists in the nucleoid, which is a region in the cell without a membrane enclosing it.