Bacteria are unicellular microorganisms with a simple structure lacking membrane-bound organelles and a defined nucleus. They have a cell wall made of peptidoglycan, which gives them their shape and is resistant to internal and external pressures. Bacteria have various extensions, including flagella, fimbriae, and pili, which help them move and attach to other objects. They also have DNA floating freely within the cytoplasm and ribosomes that create proteins.
The structure of bacteria is simpler than that of other organisms. Bacteria are microorganisms that lack membrane-bound organelles and a well-defined nucleus. They usually adopt one of four shapes, depending on the type of bacterium, and have numerous appendages with distinct functions.
Bacteria are unicellular, which means they consist of only one cell. Everything bacteria need to survive and reproduce, except food, is contained within this single cell. As such, the bacterial structure has developed in ways that allow the cell to carry out its tasks efficiently.
Bacteria are prokaryotes, meaning they don’t have an organized nucleus. The nucleus is the organelle that houses deoxyribonucleic acid (DNA) and the genetic material necessary for replication in more evolved cells. Despite the absence of a nucleus, bacteria still possess DNA, but it floats freely within the cytoplasm.
A cell wall surrounds the cytoplasmic, or inner, region of bacteria and serves as a support structure for the entire organism. The underlying layer of the cell wall is formed by peptidoglycan, a molecule composed of amino acids and sugars. This is a unique feature of bacteria and is what makes the cell wall resistant to both internal and external pressures.
Peptidoglycan gives the bacterium its shape. The shape of a given cell is usually distinct from that species and is an important detail in identifying unknown species. Two common shapes for bacteria are the bacillus, which is rod-shaped, and the spirillum, which is spiral-shaped. Other common forms are coccus, or spherical, and filamentous, in which individual cells grow in length but do not separate.
The cell wall lining is a membrane that selectively allows molecules to enter and leave the cell. The cytoplasm fills the area within the cell membrane. Inside the cytoplasm are the chromosomes, the DNA of the cell. The cytoplasm also contains the ribosomes which create the proteins used by the cell.
On the outside of the cell wall, various extensions exist to help bacteria perform actions such as moving and attaching to other objects. Flagella, strands of protein, are found on the outside of the body and move bacteria through its environment. Bacteria can have one or more flagella depending on the species.
Another surface feature of bacteria is the fimbriae. These protein strands are used by bacteria to attach themselves to other structures. They exist over the entire surface of the bacterium and are much smaller than flagella. A third component is a threadlike protein extension called the pilus, which is also found on the outside of the cell. Pili helps in conjugation and bacterial attachment.
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