ABSTRACT
Bacteria are primitive organisms classified as prokaryotes, with a primitive type of nucleus lacking a clearly defined membrane. Most of the genetic information in a bacterial cell is carried on a single chromosome with double-stranded deoxyribonucleic acid (DNA) in a closed circular form. A chromosome is the carrier of genes (the factors that control inherited traits). Genes are deoxyribonucleic acids that are linked and aligned on the chromosome. Chromosomes are located in the chromatin body of the bacteria. In addition, some bacterial cells contain extrachromosomal DNA as plasmids. Plasmids are circular DNA molecules that are generally dispensable and not essential for cell growth and division. However, they confer traits such as antibiotic resistance or pathogenicity on the host organism. Plasmids replicate independently of the chromosomes and can pass from one bacterial cell to another with ease. Some bacteria contain episomes, which are also autonomous and dispensable genetic elements similar to plasmids. Unlike plasmids, however, episomes can exist even as integrated with the chromosome. Generally, the bacteria containing plasmids do not have episomes and vice versa. Transposons, mobile DNA segments that can insert into a few or several sites in a genome, are found in some bacteria. Transposons are transposable genetic elements (the word transpose means “alter the positions of” or “interchange”) that are capable of moving between prokaryotes and eukaryotes.
