Prokaryotic Cell Characteristics PDF

**Overview** Read this and watch the video to learn about the unique characteristics of prokaryotic cells. **Unique Characteristics of Prokaryotic Cells** Cell theory states that the cell is the fundamental unit of life. However, cells vary significantly in size, shape, structure, and function. A...

**Overview** Read this and watch the video to learn about the unique characteristics of prokaryotic cells. **Unique Characteristics of Prokaryotic Cells** Cell theory states that the cell is the fundamental unit of life. However, cells vary significantly in size, shape, structure, and function. At the simplest level of construction, all cells possess a few fundamental components. These include **cytoplasm** (a gel-like substance composed of water and dissolved chemicals needed for growth), which is contained within a plasma membrane (also called a cell membrane or cytoplasmic membrane); one or more chromosomes, which contain the genetic blueprints of the cell; and **ribosomes**, organelles used for the production of proteins. Beyond these basic components, cells can vary greatly between organisms, and even within the same multicellular organism. The two largest categories of cells---**prokaryotic cells and eukaryotic cells**---are defined by major differences in several cell structures. Prokaryotic cells lack a nucleus surrounded by a complex nuclear membrane and generally have a single, circular chromosome located in a nucleoid. Eukaryotic cells have a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes (Chan, 2010). All plant cells and animal cells are eukaryotic. Some microorganisms are composed of prokaryotic cells, whereas others are composed of eukaryotic cells. Prokaryotic microorganisms are classified within the domains Archaea and Bacteria, whereas eukaryotic organisms are classified within the domain Eukarya. The structures inside a cell are analogous to the organs inside a human body, with unique structures suited to specific functions. Some of the structures found in prokaryotic cells are similar to those found in some eukaryotic cells; others are unique to prokaryotes. Although there are some exceptions, eukaryotic cells tend to be larger than prokaryotic cells. The comparatively larger size of eukaryotic cells dictates the need to compartmentalize various chemical processes within different areas of the cell, using complex membrane-bound organelles. In contrast, prokaryotic cells generally lack membrane-bound organelles; however, they often contain inclusions that compartmentalize their cytoplasm. **Figure S1, 1.1** illustrates structures typically associated with prokaryotic cells. A prokaryotic cell contains a cell membrane, chromosomal DNA that is concentrated in a nucleoid, ribosomes, and a cell wall.Figure S1, 1.1 A typical prokaryotic cell contains a cell membrane, chromosomal DNA that is concentrated in a nucleoid, ribosomes, and a cell wall. Some prokaryotic cells may also possess flagella, pili, fimbriae, and capsules.Image description\ Access for free at https://openstax.org/books/microbiology/pages/1-introduction **Common Cell Morphologies and Arrangements** Individual cells of a particular prokaryotic organism are typically similar in shape, or **cell morphology**, however, prokaryotic organisms are not multicellular. Although thousands of prokaryotic organisms have been identified, only a handful of cell morphologies are commonly seen microscopically. **Figure S1, 1.2** names and illustrates cell morphologies commonly found in prokaryotic cells. Figure S1, 1.2 A table detailing the name, description, illustration, and image of six different prokaryotic cell shapes. (credit "Coccus" micrograph: modification of work by Janice Haney Carr, Centers for Disease Control and Prevention; credit "Coccobacillus" micrograph: modification of work by Janice Carr, Centers for Disease Control and Prevention; credit "Spirochete" micrograph: modification of work by Centers for Disease Control and Prevention)Image description\ Access for free at https://openstax.org/books/microbiology/pages/1-introduction **Common Prokaryotic Cell Arrangements** In addition to cellular shape, prokaryotic cells of the same species may group together in certain distinctive arrangements depending on the plane of cell division. Some common arrangements are shown in **Figure S1, 1.3**. Common prokaryotic cell arrangements.Fig S1, 1.3 A table detailing the name, description, and illustration of seven different prokaryotic cell arrangements.Image description\ Access for free at https://openstax.org/books/microbiology/pages/1-introduction **Osmotic Pressure** In most prokaryotic cells, morphology is maintained by the **cell wall** in combination with cytoskeletal elements. The cell wall is a structure found in most prokaryotes and some eukaryotes; it envelopes the cell membrane, protecting the cell from changes in **osmotic pressure**. Osmotic pressure occurs because of differences in the concentration of solutes on opposing sides of a semipermeable membrane. Water is able to pass through a semipermeable membrane, but solutes (dissolved molecules like salts, sugars, and other compounds) cannot. When the concentration of solutes is greater on one side of the membrane, water diffuses across the membrane from the side with the lower concentration (more water) to the side with the higher concentration (less water) until the concentrations on both sides become equal. This diffusion of water is called **osmosis**, and it can cause extreme osmotic pressure on a cell when its external environment changes. **Key Terms** - **cell wall:** a structure in the cell envelope of some cells that helps the cell maintain its shape and withstand changes in osmotic pressure - **cytoplasm:** the gel-like material composed of water and dissolved or suspended chemicals contained within the plasma membrane of a cell - **cell morphology:** cell shape, structure, and arrangement, as viewed microscopically - **osmosis:** diffusion of water across a semipermeable membrane - **osmotic pressure:** the force or pressure generated by water diffusing across a semipermeable membrane, driven by differences in solute concentration across the membrane - **prokaryotic cell:** a cell lacking a nucleus bound by a complex nuclear membrane - **eukaryotic cell:** has a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes - **ribosome:** a complex intracellular structure that synthesizes proteins