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Bacteria are prokaryotic unicellular organisms with a cell wall made of peptidoglycan. They lack nuclei and membrane-bound organelles but have external structures such as flagella, pili, and fimbrae. The cell membrane mediates transport, and the genetic information is encoded in a circular chromosome and plasmids. Ribosomes are the most basic intracellular structures, but some bacteria have gas vesicles and a cytoskeleton.
Bacteria are unicellular organisms that have a prokaryotic cell structure. While bacterial cells vary in some structural elements, such as size and shape, they all share common characteristics of prokaryotes. Prokaryotic cells are distinctive in that they do not have nuclei or other membrane-bound organelles.
The bacterial cell is protected and contained by a cell wall, made up of peptidoglycan, a sugar and a protein polymer. Bacteria with thick cell walls are referred to as gram positive, while those with thin cell walls surrounded by a lipid membrane are called gram negative. The cell wall protects the cell from the effects of turgor pressure, which results from the higher concentration of solute within the cell compared to the surrounding environment of the cell.
Some bacterial cells have external structures. Flagella, which are long, flexible structures made of the protein flagellin, extend from the cell wall and give the bacterial cell greater motility. Pili and fimbrae are short tubes of proteins found among Proteobacteria and allow the bacterial cell to attach itself to a substrate or another bacterial cell.
Separating the cytoplasm, or internal fluid of the cell, from the cell wall is the cell membrane. This membrane acts as a mediator in the transport of material in and out of the cell. The bacterial cell membrane is a phospholipid bilayer made up of fatty acids and is permeable only to certain ions and molecules.
The inside of the bacterial cell is quite simple, as prokaryotic cells don’t contain many internal structures. The genetic information of a bacterial cell is encoded in a supercoiled structure of deoxyribonucleic acid (DNA) suspended in the region known as the nucleoid. The bacterial chromosome is usually circular in shape.
Other small pieces of DNA known as plasmids float independently in the cytoplasm apart from the main chromosome. These fragments code for non-essential traits and can be exchanged between bacteria. The lack of a membrane-bound nucleus allows a bacterial cell’s DNA to interact more directly with ribosomes, which are responsible for the process of translating or transferring genetic data.
Ribosomes and the bacterial chromosome are the most basic intracellular structures found in the cytoplasm of a bacterial cell, although some types of bacteria include more complicated structures. For example, some types of bacterial plankton have gas vesicles in their cells, which allow them to regulate their buoyancy in the water. Structural filaments comprising a cytoskeleton have also been observed in bacterial cells.
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