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Learning objectives

  • Explain the distinguishing characteristics of prokaryotic cells
  • Describe common cell morphologies and cellular arrangements typical of prokaryotic cells and explain how cells maintain their morphology
  • Describe internal and external structures of prokaryotic cells in terms of their physical structure, chemical structure, and function
  • Compare the distinguishing characteristics of bacterial and archaeal 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. Y.-H.M. Chan, W.F. Marshall. “Scaling Properties of Cell and Organelle Size.” Organogenesis 6 no. 2 (2010):88–96.

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. [link] illustrates structures typically associated with prokaryotic cells. These structures are described in more detail in the next section.

A diagram of a rod-shaped prokaryotic cell. The thick outer layer is called the capsule, inside of that is a thinner cell wall and inside of that is an even thinner plasma membrane. Inside of the plasma membrane is a fluid called the cytoplasm, little dots called ribosomes, small spheres called inclusions, a small loop of DNA called a plasmid, and a large folded loo of DNA called the nucleoid. Long projections start at the plasma membrane and extend out of the capsule; these are called flagella (singular: flagellum). A shorter projection is labeled pilus. And many very short projections are labeled fimbriae.
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.

Common cell morphologies and arrangements

Individual cells of a particular prokaryotic organism are typically similar in shape, or cell morphology . Although thousands of prokaryotic organisms have been identified, only a handful of cell morphologies are commonly seen microscopically. [link] names and illustrates cell morphologies commonly found in prokaryotic cells. 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 [link] .

Questions & Answers

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Many poeple are die due to covid-19 virus
AMINU Reply
they become sick due to millions bacteria, fungi and some insects that make plants as their host.
charles Reply
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charles Reply
classify microorganisms.
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protozoa' bacteria' virus' algai' archea'
Cabdifitaax
protozoa
Ayesha
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mutant having a requirement for a certain growth factor is called a(n)
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is the smallest part of any material that cannot be broken up by chemical means
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Aseptate hyphae are seen in
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CHEMISTRY
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biology
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Ahmed
Arthropod is a large division of jointed-foot Invertebrates such as Insects, centipedes and others so Insect is a part of the division or the phylum
hilina
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describe binary fission
Queen Reply
in which parent cell devides into two daughter cells
Iqra
single parent cell
Tean
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Mary Reply
Antonie van Leeuwenhoek , he is father of microbiology and Louis Pasteur is father of modern microbioloy.
Arshad
Anton van leeuwenhoek ( He descovered bacteria in 1679)
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AMINU Reply
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Madrine
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Joy Reply
a single celled organism with finger like extensions
janet
they could either be free living or parasitic
janet
is an organisms with no shape
Joy
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is the branch that deals with microorganisms
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is the science which deals with the study of microorganisms whether they may be plants or animals .
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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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