Bacteria are prokaryotic organisms that reproduce asexually. Bacterial reproduction most commonly occurs by a type of cell division called binary fission. Binary fission involves the division of a single cell, which results in the formation of two cells that are genetically identical. In order to capture the binary fission process, it is useful to understand the structure of bacterial cells.
Bacteria have different cell shapes.
The most common bacterial cell shapes are spherical, rod-shaped, and spiral. Bacterial cells typically contain the following structures: a cell wall, cell membrane, cytoplasm, ribosomes, plasmids, flagella, and a nucleotide region.
- Cellular wall. The outer covering of the cell that protects the bacterial cell and gives it shape.
- Cytoplasm. A gel-like substance composed primarily of water that also contains enzymes, salts, cellular components, and various organic molecules.
- Cell membrane or plasma membrane. It envelops the cytoplasm of the cell and regulates the flow of substances in and out of the cell.
- Flagella. Long, whip-like protrusion that aids cellular locomotion.
- Ribosomes. Cell structures responsible for the production of proteins.
- Plasmids Gene-carrying circular DNA structures that are not involved in reproduction.
- Nucleoid Region. The area of the cytoplasm that contains the only bacterial DNA molecule.
Most bacteria, including Salmonella and E. coli, reproduce by binary fission.
During this type of asexual reproduction, the single DNA molecule replicates and both copies adhere, at different points, to the cell membrane. As the cell begins to grow and lengthen, the distance between the two DNA molecules increases. Once the bacteria nearly double their original size, the cell membrane begins to pinch inward at the center.
Some bacteria are capable of transferring fragments of their genes to other bacteria that come into contact. During conjugation, one bacterium connects to another through a protein tube structure called a pilus. Genes are transferred from one bacterium to another through this tube.
